2 Acute Trauma and Chronic Overuse (According to Region)

2.1 Cranial Vault, Facial Bones, and Skull Base

2.1.1 Fractures of the Cranial Vault

Radiography. Conventional radiographs are obsolete for evaluating skull trauma as they may demonstrate fractures but not associated intracranial pathology. Furthermore, studies have shown that only approximately 50% of patients with intracranial hemorrhage also have a fracture. When radiographs are obtained, confusion can arise from normal variants that may simulate fractures including vascular grooves, sutures, synchondroses, and irregularities of the internal table. Fracture lines may cross these normal structures and their lack of sclerotic margins is often helpful in diagnosis ( Fig. 2.1).

CT. Indications for obtaining a CT examination after head injury include impaired consciousness, persisting vomiting, retrograde amnesia, seizure, severe (penetrating) trauma, multiple injuries, or signs of a basilar skull fracture.

Indirect signs of a fracture should be noted: opacification or air–fluid levels in the paranasal sinuses, the mastoid cells, and the middle ear cavity, or air in the subarachnoid space.

US. Ultrasound is only used in children. Palpable cephalohematomas associated with skull contusions can be well assessed using ultrasound, as can possible skull fractures. In these cases it is important to distinguish between fractures and cranial sutures. An adjacent epidural or subdural hematoma must be excluded in the presence of a displaced or impacted skull fracture, if necessary with the use of a CT scan.

MRI. MRI has little if any role in the diagnostic work-up of acute head injury.

Special features in children. Strict criteria must be applied when considering the use of radiography in children, especially after mild head injury Guidelines on the use of imaging of children after mild head trauma are issued by national societies in many countries and should be consulted. Moderate and severe head injuries, however, require immediate diagnostic imaging with CT.

2.1.2 Basilar Skull Fractures

Pathology. Basilar skull fractures commonly occur with head trauma. They preferentially involve the orbital roof, cribriform plate, petrous pyramid of the temporal bone, or the occipital bone. The central parts of the skull base are less frequently involved. These fractures may be associated with injuries to the neurovascular structures passing through this region (cranial nerve injuries, cerebrospinal fluid fistulas, carotid aneurysms, sinus cavernosus fistulas, etc.; Figs. 2.2 and 2.3). Lesions of the optic nerves or chiasm are common complications of injuries of the middle or anterior skull base. Posttraumatic cerebrospinal fluid fistulas are most commonly found in the region of the cribriform plate where the fractures typically course along the thin parts of the bone. Fractures of the posterior skull base often extend from elsewhere in the skull, but primary fractures in this region often result in a fatal brainstem injury.

Radiography. Conventional radiographs have no role in evaluating this type of injury.

CT. High-resolution multidetector CT with a slice thickness of 0.5 to 1.0 mm (with or without 3D reconstructions) is the standard imaging technique in this clinical scenario.

MRI. MRI is employed as a supplementary modality when injury to neurovascular structures is suspected. Absolute indications for its use are brainstem injuries and contradictory or equivocal findings on CT.

2.1.3 Fractures of the Petrous Bone

Longitudinal fractures of the petrous bone are more common, representing 70 to 80% of all petrous bone fractures. They course along the longitudinal axis of the temporal bone and through the roof of the middle ear cavity, to end in the region of the tensor tympani muscle ( Fig. 2.4). The region around the geniculate ganglion is often involved (10–20% of these cases are associated with facial nerve injuries). They often result in dislocation of the ossicular chain and conductive hearing loss. These carry a risk of an associated ascending infection from the external auditory canal, found in 20% of all fractures of the petrous bone.

Transverse fractures of the petrous bone begin at the posterior surface of the pyramid, traverse the roof of the internal auditory canal and also proceed toward the geniculate ganglion. They usually terminate in the musculotubal canal ( Figs. 2.5 and 2.6). Symptoms depend on the course of the fracture and may include sensorineural deafness and/or vertigo and spontaneous nystagmus. The facial nerve is injured in up to 50% of cases.

CT. Using the data from axial thin-slice CT scanning, coronal reconstructions are usually helpful for assessing the course of the fracture. Indirect signs of a fracture are opacification of the mastoid cells and/or the tympanon.

MRI. If hearing loss and/or facial nerve paralysis is present, MRI is indicated to directly evaluate the facial nerve and exclude a hematoma.

Important findings. It is important to search particularly for fractures involving the labyrinth, the internal auditory canal, and the facial nerve as well as dislocation of the ossicular chain.

2.1.4 Facial Bone Fractures

Fracture of zygomatic arch. This is best visualized with the axial view (so called bucket-handle view) ( Fig. 2.8). More displaced fractures are of therapeutic relevance. In small children, the zygomatic arch should be assessed primarily by ultrasound.

Fracture of the zygoma. A common injury is the tripod fracture, in which the bony connections of the zygoma with the adjacent bones are disrupted or fractured ( Figs. 2.9 and 2.10). Its depiction is achieved with paranasal sinus views and/or lateral views. CT is used in equivocal cases.

Orbital fracture. Fractures of the thin orbital floor and the thin medial lamina papyracea are common. Herniation of orbital contents (fat, inferior rectus muscle) into the maxillary sinus may complicate this type of fracture ( Figs. 2.11–2.13). Typical indirect signs of a fracture include the “hanging drop” sign (see Figs. 2.11 and 2.12) and orbital emphysema. The term blow-in fracture is used when an orbital wall fracture results in bone being displaced into the orbit. Diagnostic imaging typically begins with orbital radiographs; a CT scan is indicated when a fracture has been detected (to search for other fractures, define the extent of the fracture, or assess for an associated hematoma) and in equivocal cases.

Midfacial Fractures

Severe facial trauma often results in complex transfacial injuries that are difficult to define and classify. The Le Fort classification system has proven useful in this regard ( Fig. 2.14):

• Le Fort I: Separation of the alveolar process from the rest of the maxilla (floating palate). All the walls of the maxillary sinuses are fractured.

• Le Fort II: Pyramid-shaped fracture (“pyramidal fracture”) with separation of the central midface. The fracture line courses through the root of the nose, the medial orbital wall, and the orbital floor. The medial wall of the maxillary sinus is preserved.

• Le Fort III: This fracture results in separation of the face from the skull. The fracture line courses bilaterally through the root of the nose, medial orbital wall, orbital floor, and lateral orbital wall. There are additional fractures of the zygomatic arches.

The common feature of all Le Fort fractures is involvement of the pterygoid processes ( Fig. 2.15).

It is very common to find combinations of different (Le Fort) fracture types in one or even both halves of the midface ( Fig. 2.16). Particular attention should be paid to possible associated injuries (anterior skull base, mandible, etc.).

CT. High-resolution CT is the modality of choice for suspected complex midfacial injuries. 3D reconstructions are often helpful for providing better visualization.

MRI. When associated cranial nerve injury and/or brain injury are suspected, MRI is indicated.

Mandibular Fractures

Mandibular fractures are commonly multiple (50–60% of cases). Fractures that course through the dental alveolus are regarded as open fractures. A differentiation is made between fractures of the mandibular body, the mandibular angle, and the mandibular ramus as well as those that involve the mandibular joint.

Radiography. Standard radiographs are typically obtained. An orthopantomogram may be helpful.

CT. CToffers the most exact fracture depiction, which is oftenessential for an optimal treatmentoutcome ( Fig. W2.1). In addition to 3D reconstructions ( Fig. W2.2), orthopantomograms can also be generated from the CT data set. A more recent technique, known as cone beam CT, is also proving to be useful ( Fig. W2.3).

2.2 Spine

2.2.1 Anatomy, Variants, Technique, and Indications

Anatomy. See Chapter 2.2.1 and Fig. W2.4.

Technique and Indications

Radiography. Radiographs are still commonly used for screening in cases of mild spinal trauma. The lateral view is the most important. It should be performed without repositioning the patient. Severe spinal injuries should be immediately investigated with CT because the extent of injury is often underestimated on conventional radiographs. The need for lateral and swimmer oblique views, and above all functional studies, should be assessed critically with regard to their diagnostic value. If a multislice CT unit is available, then conventional radiographs of the spine should be dispensed with in the patient who has sustained significant trauma.

Apart from evidence of fracture lines and/or fragments, indirect signs of spinal injury include:

• Loss of vertebral height.

• Widening or deformity of the vertebral body.

• Linear sclerosis within a vertebral body.

• Irregularity or interruption of reference lines ( Figs. 2.17 and 2.18).

• Segmental malalignment (this is best recognized by observing the posterior vertebral line; segmental fanning of the facet joints and spinal processes is a very helpful sign of significant injury ( Fig. 2.19).

• Widening or narrowing of an intervertebral disk space relative to adjacent levels.

• Widened prevertebral soft tissues (in the cervical spine this should not exceed 7 mm in adults at the level of the inferior margin of C2) ( Fig. 2.20; see also Fig. 2.17). However, a normal appearance of the prevertebral soft tissues does not exclude significant underlying bone or ligament injury. Attention should also be paid to any displacement of the prevertebral fat stripe or contour of the trachea.

2.2.2 Mechanisms of Injury and Classifications

One of the most commonly used classification systems for spinal injuries is that of Magerl, which is based on the current AO classification system ( Fig. 2.21). It also attempts to take into consideration discoligamentous injury patterns as evident on MRI scans. With the Magerl classification, the severity of the injury increases from Types A through C as well as within the types from groups 1 through 3. Type A and Type B injuries are often combined.

In the United States, the Thoracolumbar Injury Classification and Severity Score (TLICS), published in 2005 by A. R. Vaccaro et al. is currently used ( see references in Chapter 2.2.2).

Compression Injuries

Compression injuries result from vertical forces impacting on the vertebra from a cranial or caudal direction. The fracture is usually located in the thoracolumbar region and characterized by widening of the vertebral body and loss of vertebral height as well as by disruption of the vertebral cortex. The Type A1 lesion ( Fig. 2.21) is a failure of the anterior column resulting in an isolated vertebral body injury. Subgroups of A1 fractures include

• A1.1: a pure impact fracture of the superior end plate.

• A1.2: a wedge type fracture.

• A1.3: a vertebral body collapse.

A1.3 fractures are typical osteoporotic compression fractures that result in compression of both end plates with an intact posterior wall (the so-called “fish” or “fish mouth” vertebra).

Whereas A1 and A2 fractures are usually stable injuries ( Figs. 2.21 and 2.22),

A3 burst fractures ( Figs. 2.23 and 2.24) are often considered to be unstable due to involvement of the posterior wall and contiguous intervertebral disks and in some cases may require surgical stabilization, especially when the burst fracture is complete (A3.3) (see Fig. 2.24). Comminuted fractures with displacement fracture fragments in the spinal canal often result in associated neurologic complications. If the neurologic deficit does not correlate with the extent of the spinal canal stenosis, then a search should be made for an associated epidural hematoma, intervertebral disk protrusion or spinal cord injury, in which case an MRI scan is the diagnostic modality of choice. CT myelography is an alternative for a patient with a contraindication for MRI or if MR scanning is unavailable.

Extension Injuries

Extension injuries are less common than those related to flexion but are frequently overlooked or underestimated due to the often subtle associated radiographic findings. They result in neurologic damage less commonly than do flexion injuries. They often occur in older patients who sustain a ground-level fall, striking their head, producing hyperextension of the cervical spine. The cervical spine is particularly susceptible to hyperextension injuries due to its exposed position and its high degree of sagittal mobility with the center of rotation at the level of the articular processes. Vertebral alignment, including the spinolaminar line, may be normal after injury.

Extension teardrop fracture. A hyperextension injury (typical case: a dive head-first into shallow water) results in a genuine avulsion of bone at the attachment of the anterior longitudinal ligament ( Figs. 2.26–2.28). Typical levels of injury include the lower cervical spine (often in young patients) as well as in the C2 region (especially in older patients). An important point is the fact that the teardrop fragment represents the fixed point because it has remained firmly attached to the anterior longitudinal ligament, while the associated vertebral body has torn away, resulting in a triangular fragment along the anterior inferior margin of the involved vertebra on radiographs. However, neither radiography nor CT reflects the full degree of soft tissue pathology associated with such injuries, and MR imaging is indicated in these cases to identify ligamentous and spinal cord injuries.

Posterior subluxation/dislocation. Rupture of the anterior and (rarely) the posterior longitudinal ligaments as well as the intervertebral disk, combined with dislocation/subluxation of the facet joints and, in some cases, additional fractures through the neural arches results in transient posterior translation of the vertebra ( Fig. 2.29). This injury is highly unstable and is associated with severe neurologic deficits. It most often occurs in the mid-cervical region (C4–C6) and at the thoracolumbar junction. Because the vertebra frequently reduces spontaneously, spinal alignment may appear normal on radiographs. Indirect, often subtle, findings such as anterior soft tissue swelling or anterior widening of a disk space should prompt further evaluation with MRI to assess the degree of ligamentous and spinal cord injury. Such hyperextension injuries are particularly common in older patients with degenerative spines in whom the canal is already narrowed by osteophytes and redundant ligaments (Chapter 2.2.4). These patients often present with a central cord syndrome in which the neurologic symptoms are more pronounced in the upper than in the lower extremities.

Flexion Injuries

Flexion injuries are the most commonly encountered in the spine. They are the result of excessive flexion of the spine in which the axis of rotation is usually at the level of the dorsal third of the intervertebral disk space. The anterior vertebral segments are maximally compressed, while the posterior are distracted. Typical compression/distraction injuries can develop as a result of this mechanism such as transverse disruption of the posterior ligamentous complex (Type B1 injury) or transverse bony disruption (spinous processes, pedicles, pars interarticularis; Type B2) ( Figs. 2.30–2.33).

With high-velocity flexion loading, subluxation/dislocation of the facet joints occurs, resulting in some cases in complete bilateral dislocation and locked facets. This may result from pure discoligamentous disruptions without an associated fracture (see Fig. 2.33).

Unilateral facet joint dislocations or fractures occur when there is an additional rotational force, which is often underestimated on radiographs. Spontaneous fracture reduction can occur with the patient in a supine position. Pure anterior compression fractures are stable, whereas all flexion–distraction injuries are potentially unstable.

Anterior wedge fracture. The mildest form of flexion injury involves anterior compression of the vertebral end plate, which remains intact posteriorly. A stronger force produces more extensive compression with more marked formation of a wedge-shaped vertebra and possible involvement of the posterior body (middle column). A wedge-shaped vertebra can develop not only anteriorly but also laterally. The osteoporotic wedge-shaped vertebra will be discussed in Chapter 8.

Flexion teardrop fracture. In this type of fracture flexion has resulted in separation of a triangular, or “teardrop,” fragment from the anteroinferior corner of the vertebral body ( Fig. 2.34; see also Figs. 2.26 and 2.35). The vertebral body is split in the coronal plane, with the posterior fragment protruding into the spinal canal. The fracture is most frequently located at the lower cervical spine (70% at C5). The most important feature of this injury, however, is that it results in disruption of the posterior longitudinal ligament and is therefore extremely unstable. It also commonly results in spinal cord injury.

Chance fracture. A flexion injury with the center of rotation moved to the anterior abdominal wall (as is seen with a lap seatbelt) results in significantly magnified tensile forces in the spine and a horizontally orientated disruption of the vertebral column. These fractures most commonly involve the mid-thoracic to mid-lumbar vertebra with fractures involving not only the vertebral body but also the pedicle and other posterior elements, rendering these highly unstable ( Figs. 2.35 and 2.36). Of note, the disruption may predominantly involve the soft tissues (disk, ligaments) which will be best evaluated with MR imaging. These fractures may also be associated with anterior vertebral compressions (Type A fracture) and angular hyperkyphosis.

Anterior subluxation/dislocation. This is a severe form of flexion–distraction injury that is characterized by disruption of the posterior ligamentous complex together with a tear of the posterior longitudinal ligament. The intervertebral disk is also commonly involved (discoligamentous disruption). This injury is highly unstable. Rupture of the posterior anulus fibrosus can in rare cases result in traumatic disk extrusion. This results in anterior tilting of the vertebra over the underlying vertebra with fanning of the spinous processes, incomplete articulation of the facet joints, and anterior displacement of the subluxed vertebra by more than 50%. In marked cases, unilateral or bilateral facet dislocation can also develop (known as locked facets; Fig. 2.37). This is found predominantly at the lower cervical spine. It involves the tip of the dislocated inferior articular facet (superior vertebral body) being locked in front of the superior facet of the inferior vertebral body. A pure unilateral facet dislocation is a relatively stable injury as a result of interlocking of the dislocated facet joints and neurologic symptoms are uncommon. Nevertheless, the rotatory malalignment requires correction. The reverse hamburger-bun sign and the headphone sign on axial images are helpful imaging findings in these cases ( Fig. 2.38). Bilateral facet dislocation commonly results in traumatic spinal canal stenosis with neurologic deficits, which can occasionally develop after some delay.

Rotational Injuries

Rotational injuries usually originate from severe flexion trauma combined with a torsional vector that leads to rupture of the posterior ligamentous and/or discoligamentous complex and/or fracture of the facet joints, resulting in rotational malalignment of the spinal axis. The discoligamentous involvement produces unstable spinal injuries that are associated with a high incidence of concomitant spinal cord injuries. The findings of asymmetrical dislocation or fracture of the facet joints and/or juxta-articular neural arch fractures point to a rotational component ( Fig. 2.39). Furthermore, fractures of the proximal parts of the ribs, transverse processes, and spinous processes are indirect signs of a rotational injury. Because of the risk of long-term rotatory and translational malalignment it is imperative to carefully assess images of spinal injuries (burst fractures in particular) for rotational malalignments. Rotational injuries—albeit uncommon—tend to be underestimated and underdiagnosed in multiply injured patients.

Unilateral facet dislocation occurs as a result of a combination of hyperflexion with rotation and is found predominantly in the lower cervical spine (see Fig. 2.39). In only one-third of cases is it associated with a fracture of an articular process. There is often neurologic compromise due to associated foraminal narrowing.

Translational Injuries (Shearing Injuries)

These injuries are the result of enormous horizontal or oblique forces. Usually the lower half of the body is fixed while the upper segment moves relative to it. The ligaments are always disrupted, even without associated fracture, if the superior spinal components are displaced dorsally. The vertebroligamentous injury pattern is complex. These are usually Grade C3 injuries according to the AO Classification (see Fig. 2.21), even though the rotational component is not always apparent (effect of positioning, spontaneous reduction in immobilization devices; Figs. 2.40 and 2.41). These injuries are often associated with severe neurologic symptoms, and multilevel injuries are commonly found in the rigid spine (Chapter 2.2.4).

Special Fracture Types That Do Not Threaten Spinal Stability

Transverse process fracture. Fractures of the lumbar transverse processes are predominantly the result of direct blows and usually of no clinical relevance. However, they are important as warning signs because these fractures are often associated with concomitant injuries such as other spinal injuries (possibly at a significant distance), and especially injuries to abdominal and retroperitoneal organs (e.g., renal lacerations) ( Fig. 2.42).

Clay-shoveler’s fracture. This fracture of the tip of a spinous process occurs as a result of an abrupt flexion of the head and neck relative to the tight nuchal ligaments. It is a bony avulsion fracture at the attachment of the supraspinatus ligament at the cervicothoracic junction level, such that both this ligament and the posterior longitudinal ligament remain intact. The line of fracture is usually vertical through the dorsal portion of the spinous process and it is often a chronic, incidental finding (evidenced by sclerotic margins with or without associated calcification of the nuchal ligament; Fig. 2.43). However, clay-shoveler’s fractures must not be confused with an oblique Chance fracture of the spinous process or with fractures of the spinous process, which are indication of a severe dorsal distraction injury.

Sequelae of Trauma to the Sacral and Coccygeal Bones

Fractures of the sacrum. These are usually the result of a direct trauma (fall). The majority occur in combination with pelvic fractures. Denis distinguishes three types:

• Type I: Lateral to the neural foramina, no neurologic symptoms.

• Type II: Transforaminal sacral fractures, commonly associated with neurologic symptoms ( Fig. 2.44).

• Type III: Central fractures involving the sacral canal; neurologic symptoms are common.

Sacral fractures are overlooked on survey radiographs in up to 50% of cases. A CT scan is therefore always indicated if there is a high degree of clinical suspicion or there are indirect radiographic signs (transverse process fractures of L5, anterior pelvic ring fracture, symphysis disruption).

2.2.3 Special Traumatology of the Cervical Spine and the Craniocervical Junction

The Magerl classification system (based on the AO system) is used for classifying fractures of the subaxial cervical, thoracic, and lumbar spine (the latter two may also be classified according to the TLICS system, see Chapter 2.2.2). Other classification systems have been developed for the upper cervical region (from the craniocervical junction to C2).

Fractures of the Occipital Condyles

Fractures of the occipital condyles are rare and are usually the result of axial blows to the head; they are best classified using the Anderson and Montesano system:

• Type I: Compression fracture of the occipital condyles.

• Type II: Basilar skull fracture that extends to involve the occipital condyle region. These fractures are usually stable and only identified on appropriate CT scan sections ( Fig. 2.45).

• Type III: Avulsion fractures with bony ligamentous avulsions (alar and cruciform ligaments of the atlas) on the inner surface of the condyles; these injuries are potentially unstable. They often occur in combination with brainstem injuries and are the result of severe trauma. The often subtle avulsion fragments must be carefully looked for on multiplanar CT images since they are often the only signs of severe craniocervical ligament disruption ( Fig. 2.46). MRI may be used to assess associated ligamentous and/or cord injury.

Craniocervical Dissociation

The infrequently encountered disruption of all ligaments at the craniocervical junction represents the ultimate form of craniocervical dissociation. This injury is seen after high-velocity trauma from considerable whiplash movement of the head with the body restrained; it is especially common in children owing to their large head-to-body ratio and lax craniocervical ligaments. (see the subsection “Special features of pediatric cervical spine injuries”). This injury is almost always fatal due to severe spinal cord damage, and if the patient does survive it is typically with a severe neurologic deficit.

Fractures of the Atlas

The angled position of the occipital condyles and atlantoaxial articular surfaces as well as the ring configuration of the atlas predispose the atlas to a burst fracture of its arch during axial compression (the so-called burst effect). Isolated fractures of the anterior and posterior arch of the atlas, on the other hand, are caused by hyperextension injuries. Neurologic deficits are rather rare with fractures of the atlas since they tend to result in enlargement of the diameter of the spinal canal.

The following modified fracture classification system according to Jefferson is currently in use:

• Type I: Fracture of the anterior ring of the atlas; there is often an additional fracture of the dens. Extension mechanism, usually stable.

• Type II: Fracture of the posterior ring of the atlas; the most common form. The posterior ring of the atlas is wedged between occiput and C2, resulting in the fracture. Extension mechanism, usually stable.

• Type III: Fracture of the ring involving both the anterior and posterior arches (Jefferson’s fracture; Fig. 2.47a). It occurs as a result of abnormal axial loading of the occipital condyles on the atlas with the head extended (compression fracture). This fracture is unstable if it is associated with a rupture of the transverse atlantal ligament. An indirect sign of ligament disruption on the odontoid view or on reformatted coronal CT images is bilateral displacement of the lateral articular masses of the atlas beyond the articular margins of the axis by more than 7 mm combined ( Fig. 2.47b). However, this sign may be masked in the presence of concomitant rotation, rendering a CT examination necessary for an exact assessment of the fracture.

• Type IV: Unilateral or bilateral compression fracture of the lateral masses of the atlas; stable but unfavorable prognosis with regard to the development of posttraumatic osteoarthritis of the occipital-atlantal joints.

• Type V: Fracture of a transverse process of the atlas (stable).

In addition there are a number of other nonclassified fracture types, such as a horizontal fracture of the anterior arch of the atlas due to traction of the anterior longitudinal ligament and the longus colli muscle, and the bilateral, vertical fracture of the posterior arch due to forced hyperextension of the head (which should be differentiated from a congenital unfused posterior arch of the atlas).

The assessment of traumatic rotational, atlantoaxial malalignment (subluxation or dislocation) and its differentiation from voluntary, postural rotation in the superior cranial joints are difficult. Clues for rotational injuries can include asymmetry on the AP odontoid view; in particular unilateral (rarely bilateral) loss of the atlantoaxial joint space on a correctly adjusted view (known as the wink sign; Fig. 2.48). The degree of rotation can be determined on axial CT sections (up to 45° is normal at maximum rotation), at which time pathologic anterior displacement of the atlas over the axis may also be detected.

Classification System According to Fielding and Hawkins

• Type I: Pure rotatory, unilateral atlantoaxial dislocation ( Fig. 2.49); without fracture, it is impossible to differentiate from a voluntary rotation of the head on a static CT image. Only after a dynamic examination is it possible to demonstrate a fixed rotational malalignment (when it is impossible to return the malalignment to the neutral position by turning the head to the opposite side).

• Type II: Atlantoaxial rotatory abnormality with anterior dislocation and an atlantodental interval of less than 5 mm. The transverse ligament of the atlas may be ruptured.

• Type III: Atlantoaxial rotatory abnormality with anterior dislocation and an atlantodental interval of less than 5 mm. Disruption of the transverse ligament of the atlas with instability.

• Type IV: Atlantoaxial rotatory abnormality, with the atlas displaced unilaterally or bilaterally in a posterior direction in relation to the axis (posterior dislocation); usually in the presence of a Type II fracture of the dens or an unstable dens nonunion.

Fractures of the Axis and Dens

Dens fractures are common and constitute approximately 20% of all cervical fractures. Hyperextension mechanisms are most commonly responsible for these fractures. Whereas more forceful accidents are mainly responsible in young adults, these fractures occur in the aged as a result of simple falls. Associated neurologic deficits are present in up to 30% of cases. A CT scan is best suited for assessing the fracture. Dens fractures are classified by Anderson and D’Alonzo into three types ( Fig. 2.50):

• Type I: Obliquely through the tip of the dens; actually an avulsion fracture of the alar ligaments; an extremely rare fracture.

• Type II: Transversely through the base (waist) of the dens, unstable, the most common fracture type ( Fig. 2.51). Nonunion develops in ~ 30% of cases.

• Type III: Fracture of the body of C2, commonly with involvement of an atlantoaxial joint surface; anterior dislocation in 90% of cases. This fracture is also mechanically unstable, but does not tend to proceed to nonunion.

Traumatic Spondylolisthesis of the Axis

Also termed a “hangman’s fracture”, this injury occurs as a result of extension with simultaneous vertical compression, such as that which occurs in rear-end collisions. However, other mechanisms can also result in this injury, such as a pure flexion. The most commonly used classification system is that of Effendi:

• Type I: Nondislocated fracture with intact intervertebral disk, stable.

• Type II: Involvement of the C2–C3 intervertebral disk, sagittal displacement of the body of the axis by more than 3 mm, or angulation of the dens by more than 11°, unstable ( Figs. 2.54–2.56).

• Type III: In addition to the findings with a Type II fracture, the facet joints at C2–C3 are dislocated and locked.

Neurologic complications are less common than with other injuries due to the relatively large width of the spinal canal at this level.

Whiplash Injury of the Cervical Spine

In children, skeletal structures still possess a high degree of elasticity. For this reason, bony injuries to the spine are relatively rare, even in the presence of accident-related neurologic deficits. This special feature is subsumed under the acronym “SCIWORA syndrome” (spinal cord injury without radiographic abnormality). Ligamentous laxity in childhood with associated discoligamentous flexibility results in significant degrees of movement, which can bruise, overstretch, and even disrupt the spinal cord. Intramedullary hemorrhage can also occur ( Fig. 2.57).

The decisive point is that radiological signs (fractures, dislocations) are absent despite a severe neurologic deficit. This explains the central role of MRI in such cases. Children less than 10 years of age are mostly affected, especially those under the age of 3 years. The most common site of the spinal cord injury is at the level of C2.

Another special feature of pediatric cervical injury is the vulnerability of the occipitoatlantal junction: The occipitoatlantal ligaments and membranes are unable to stabilize the still relatively large head of the child during severe deceleration events, resulting in disruption of the atlantoaxial complex and, in some cases, fatal occipitoatlantal dissociation.

Incomplete ossification or fusion of the ossification centers must not be confused with a fracture. The following are important time points of ossification ( cf. also “Variants” in Chapter 2.2.1):

• Atlas: ossification of the posterior arch at age 4 years, complete fusion during the 7th to 10th years.

• Axis: fusion of the posterior arches between the ages of 2 and 3 years with fusion with the body of C2 by the age of 7 years. The ossiculum terminale of the dens fuses with the body of the dens around the age of 11 to 12 years. Subdental synchondrosis can persist until adolescence and may be confused with a Type II fracture of the dens. An MRI scan helps in equivocal cases since true injuries are typically associated with edema in the marrow and adjacent tissues.

Anterior displacement of C2 on C3 or of C3 on C4 is a physiologic variant in ~ 20% of children up to the age of 5 years. However, alignment of the spinolaminar line is maintained in this “pseudo subluxation.”

Inadequate distension of the pharynx can often produce a prevertebral soft tissue shadow on conventional radiographs that can be mistaken for a hematoma. MRI can help in equivocal cases.

2.2.4 Injury Patterns of the “Stiff” Spine

Because of absent segmental mobility, long rigid leverages, and vertebral osteoporosis, even apparently harmless falls can result in severe fractures with discoligamentous disruptions, subluxations, or dislocations ( Fig. 2.58). The fractures often course horizontally or obliquely through an entire vertebral body, adjacent disk space and into the posterior elements; consequently all three columns of the axial skeleton are typically involved ( Fig. 2.59). Fractures are often encountered at multiple levels.

2.2.5 Stable or Unstable Fracture?

Assessment of stability of fractures of atlas and odontoid has been discussed in the sections describing those injuries (Chapter 2.2.3).

Middle and Lower Cervical Spine

There are no universally recognized classification systems for assessing the stability of injuries involving the subaxial cervical spine, but the classification system according to Magerl is increasingly being applied to this portion of the spine. While there are no absolute criteria for diagnosing instability, the following criteria may serve as guidelines:

• Horizontal translation of more than 3.5 mm between adjacent spinal segments (if the anterolisthesis or retrolisthesis is interpreted as being degenerative, then additional signs of degeneration should be clearly evident, e.g. disk space narrowing, osteophytes, etc.).

• Angulation between two adjacent vertebrae of more than 11°.

• Widening of a disk space.

• Facet joint subluxation resulting in less than 50% overlap.

• Increased interspinous distance.

Thoracic and Lumbar Spine

There is currently broad agreement with regard to criteria for assessing the stability of thoracolumbar fractures, in particular with respect to osseous injury patterns, which can be assessed using the classification system according to Magerl (Chapter 2.2.2).

Type A fractures are generally regarded as stable with the exception of Type A3, although this does not mean that they should necessarily be treated conservatively. There has been a tendency over recent years to regard Type A3 fractures as unstable (progressive collapse with malalignment of the axial skeleton and also, in the case of a large, avulsed posterior wall fragment, a possible neurologic deficit). The paradigm of the intact posterior wall as an exclusive discriminator of stability has been abandoned ( see “Anatomy” in Chapter 2.2.1).

Type B fractures are unstable due to their potential for discoligamentous disruptions secondary to flexion or extension forces. However, these can be very difficult to identify using radiography or CT when bony injuries are either absent or extremely subtle in nature. This applies, for example, to small teardrop fragments, which are an indication of a severe flexion/extension injury. It may well be helpful to postulate instability using certain metric criteria (e.g., segment angulation by more than 11°, sagittal translation by more than 3.5 mm, subluxation of the facet joints by more than 50%), but it may not always apply in particular cases. Apart from confirming the integrity of sagittal alignment, it is also very important to confirm uniformity of disk heights and interspinous distances. Additionally, congruence of the facets on either side of the spine must be confirmed when using CT.

Type C injuries pose a diagnostic challenge due to the subtle imaging findings in some of these cases. Type C injuries are rotational injuries and always result in significant instability; initially or over time, possibly resulting in a neurologic deficit. Any unilateral facet joint fracture or dislocation indicates a rotational injury. Fractures of proximal ribs and transverse processes may also reflect prior rotational trauma. The difficulty in identifying such rotational and shear injuries lies in the fact that they often reduce spontaneously during positioning and transport, thus masking the true nature of the injury.

2.2.6 Fresh or Old Fracture?

CT. CT allows a better assessment of the integrity of the vertebral cortex in acute fractures ( Fig. 2.60). Evaluation of trabecular bone is problematic, however, because trabecular injuries are often not apparent until the development of microcallus that produces bandlike sclerotic patterns in later stages (see Fig. 2.60). The presence of thin linear cancellous densities parallel to the end plates is suggestive of an acute trabecular injury, whereas during subacute stages resorption bands may also become evident.

MRI. MRI provides the most reliable way to differentiate between acute and older fractures, irrespective of their etiology. Fluid-sensitive sequences with fat suppression are well suited for detecting fracture-related edema in an acute injury. The hyperintense edema on these sequences is often bandlike, extending parallel to the superior or inferior end plates ( Fig. 2.61a). Similarly, T1W sequences will reveal corresponding hypointense fracture lines, but some normal, hyperintense fatty marrow should always be observed ( Fig. 2.61b). When the entire vertebral body is involved, the possibility of a pathologic fracture related to underlying neoplasm must be considered! IV contrast administration sometimes improves fracture line delineation.

2.2.7 Differential Diagnosis “Osteoporotic Versus Pathologic Fracture”

Table 2.1 provides an overview of radiological decision aids and important radiological signs. Image examples with explanations of the radiological signs may be found in Figs. 2.62–2.65.

2.2.8 Stress Phenomena in the Spine: Stress Reaction and Stress Fracture (Spondylolysis) of the Neural Arches

Insufficiency fractures, e.g., due to osteoporosis or associated with pregnancy, are common in the sacrum (see also Chapter 2.3.3).

2.2.9 Value of MRI in Acute Trauma

Indication for MRI

Ligament disruptions are best recognized on fat-suppressed T2W or STIR sequences (STIR = short-tau inversion recovery). Hyperflexion injuries are often associated with disruptions of the posterior ligamentous complex and can be well identified by extensive edema within the interspinous tissues ( Figs. 2.31 and 2.33). It is often possible to identify directly discontinuity and tears of the longitudinal ligaments and the ligamenta flava (see Figs. 2.33 and 2.34). Hemorrhage and dislocations of vertebral fragments can elevate, or even obscure, the longitudinal ligaments.

Disk Injury

The effects of disk injury remain uncertain, despite various staging proposals.

Traumatic disk prolapse. The occurrence of traumatic disk herniation is the focus of intense discussion—especially in the insurance law literature. Given adequate trauma, it can occur, albeit rarely ( Figs. 2.67 and 2.68). Associated findings suggesting an acute injury (soft tissue edema, ligament tears, hematomas, bone bruises) should be observed in these cases. Traumatic disk prolapse, along with the hyperflexion injury itself, may result in spinal cord injury (cord contusion or even intramedullary hemorrhage), especially in the cervical region.

Hematomas

Trauma-related spinal hemorrhage predominantly involves the epidural space; subdural subarachnoid hemorrhages are extremely rare.

Epidural hematomas are found between the periosteum of the vertebrae or vertebral arches and the dura mater of the thecal sac and extend a significant craniocaudal distance—usually over several segments. They are most commonly encountered in the ventral epidural space. In addition to uncomplicated epidural hemorrhages associated with traumatic vertebral fractures, hemorrhages associated with the epidural venous plexus will often form space-occupying hematomas that may result in compression of the cord or, less frequently the cauda equina. Rapidly progressive paraplegia makes an epidural hemorrhage an emergency situation demanding immediate intervention.

In addition to traumatic epidural hematomas, spinal hemorrhages may develop during anticoagulant therapy either spontaneously ( Fig. 2.69) or after minimal trauma. Other possible causes of epidural hematomas include spinal interventional procedures or surgery.

MRI. The MRI appearance of hemorrhage varies depending on its age. Fresh hematomas are often isointense to, and difficult to differentiate from, cerebrospinal fluid on T1W sequences, while on T2W sequences they can still appear hypointense in the acute phase but change rapidly to an intermediate or even hyperintense appearance. Typical methemoglobin formation occurs after a few days (the subacute phase) and is characterized by hyperintensity on T1W images. GRE (gradient echo) sequences can be helpful in identifying hemorrhage giving rise to typical susceptibility artifacts related to the iron content of the blood. Contrast administration can be dispensed with in the acute stage. Chronic epidural hematomas display marginal contrast enhancement. Epidural hemorrhages related to intermittent bleeding are characterized by marked signal heterogeneity.

MRI. Spinal cord contusions are evident on T2W sequences as hyperintense intramedullary lesions ( Fig. 2.67). The spinal cord signal abnormality can be either subtle and situated very distinctly at the level of the vertebral injury or occupy extensive cross-sectional areas of the cord and extend over several segmental levels. Attention should be paid to features of preexisting degenerative spinal canal stenosis (osteophytes, etc.) as these can result in cord contusion even after minor injuries. The degree of spinal cord signal abnormality (swelling, edema) correlates significantly with the ultimate prognosis. Intramedullary hemorrhage is evident as focal, sometimes only punctate alterations. Susceptibility-weighted sequences (DWI [diffusion weighted imaging], gradient echo [T2*W], or even FLAIR [fluid attenuated inversion recovery]) are therefore best suited to demonstrate intramedullary hemorrhage. Extensive intramedullary hemorrhage tends to be rare after trauma and raises the possibility of other conditions such as a cord tumor or vascular malformation but is associated with a severe neurologic deficit (symptoms of complete spinal cord injury), which aids in the diagnosis. The most severe form of traumatic cord damage is spinal cord disruption, which—provided the patient survives—is associated with spastic paraplegia or tetraplegia and the entire spectrum of autonomic dysfunction in addition to pain.

Sequelae resulting from traumatic spinal cord injuries include myelomalacia, syringohydromyelia, medullary cyst formation, tethered cord syndrome of varying degrees (posttraumatic synechiae of the thecal sac), and spinal cord atrophy.

2.2.10 Radiological Assessment after Surgery of the Spine

MRI. MRI is the best method for evaluating soft tissue structures of the spine. This applies to the spinal canal when looking for hemorrhage, recurrent disk extrusion, spinal canal injuries, myelopathy, or inflammatory conditions, as well as in assessing paravertebral soft tissues for hematoma, inflammatory changes, musculoligamentous injuries, or vascular issues (often with the aid of MR angiography). The ability to assess bone marrow is especially useful for demonstrating postoperative vertebral body edema or in cases of secondary fractures. The MRI protocol includes at least sagittal T1W and T2W sequences, axial T2W, and fat-suppressed coronal and/or sagittal T2W sequences. Obtaining additional heavily T2-weighted 3D sequences with MIP (maximum intensity projection) reconstructions can be helpful (“MR myelography”). Within the first 2 to 4 weeks postoperatively, intravenous contrast administration often leads to difficulties in interpretation due to postoperative changes and should therefore only be administered in specific situations, e.g., for suspected infection or abscess formation. Fat-suppressed sequences are often limited due to field heterogeneity caused by metallic implants, so other techniques such as inversion recovery (STIR) or subtraction imaging may be helpful. Susceptibility-weighted sequences are useful for suspected hemorrhage, and DWI sequences for suspected ischemia.

Direct sequelae. This refers to postoperative complications involving the structures surrounding the spine, such as adjacent neurovascular structures ( Fig. 2.70). In the cervicothoracic region, the trachea, the esophagus ( Fig. 2.71), or the pleural cavity may be affected by direct trauma or indirectly as a result of swelling or space-occupying hematomas.

Indirect sequelae. These include malpositioning or loosening of surgical implants and their effect on bony structures, iatrogenic instability caused by extensive resection of the posterior elements, and cement leakage during cement augmentations.

In the late postoperative stage, infection of the vertebrae, disks, paravertebral space, and especially within the spinal canal poses a challenge for diagnostic examinations.

After fusion of vertebral segments, accelerated degeneration develops in adjacent motion segments due to mechanical overuse and altered biomechanics (“junctional disease”).

Adjacent segment instability in its proper sense refers to the detection of pathologic hypermobility of motion segments above and below a fusion. It does not develop immediately after surgery but usually appears years later and is more commonly situated above the fused segments.

The diagnostic value of lateral flexion/extension studies is controversial because hypermobility is underestimated if movement is limited by pain and, conversely, translational movements of 4 mm are found in up to one-third of asymptomatic persons.

See the specialized literature for the complex topic of postoperative symptoms secondary to scarring (postnucleotomy syndrome).

Expressions Used by Surgeons

Cages and vertebral body replacement. Tilting or even penetration of cages or vertebral replacements into the adjacent vertebral end plates must be noted ( Fig. 2.72). This is particularly relevant in spines weakened by osteoporosis and not stabilized by other means, where progressive penetration by implants can ensue. Implants that are not flush with the adjacent end plates can result in progressive malalignment and should be documented.

Screws. “Suboptimal” screw positioning—such as penetration of the anterior vertebral cortex by a few millimeters; a lateral rather than concentrically medial course of the screw in the vertebral body; or injury to the medial or lateral pedicle wall—is generally of no clinical relevance. On the other hand, extrapedicular malposition of the screws through the spinal canal should be reported as it will usually require revision. Screws that impinge on the course of vessels must be mentioned and may need to be examined further by supplementary CT angiography ( Fig. 2.73). A lucent rim of more than 2 mm with sclerotic margins and/or a change of direction or penetration into the end plate over time suggest screw loosening ( Fig. 2.74).

Cement. Cement leakage into intervertebral spaces becomes possible as soon as the cement abuts the end plates of the vertebra (see Fig. 2.74c). Mild cement leakage into the paravertebral space, paravertebral veins, or the epidural venous plexus is usually asymptomatic, whereas leakage into the spinal canal with a space-occupying effect or leakage into the venous system as far as the vena cava or the azygos/hemiazygos venous system, with the associated risk of pulmonary embolism, is to be regarded as a complication ( Figs. 2.75 and W2.7).

2.3 Pelvis

2.3.1 Fractures of the Pelvic Ring

Anatomy. See Chapter 2.3.1 including Fig. W2.8.

Pathology. Injuries to the pelvic ring usually result from falls or direct impact injury. Whereas minor injuries predominate at an older age, pelvic ring fractures in younger patients are usually the result of high-energy trauma. Consequently, a host of associated injuries should be expected and are often the reason for the high mortality associated with complex pelvic fractures. Typical associated injuries include injuries to the genitourinary tract with bladder rupture and urethral avulsion, and vascular damage.

The most established classification system for pelvic ring fractures, the AO classification, is based on the classification by Tile, who subdivides the fractures into three groups:

• Stable fractures.

• Rotationally unstable fractures.

• Rotationally and vertically unstable fractures.

The history of the injury with regard to energy and force vector are important features in addition to the imaging findings (see Radiography and CT).

Classification

Type A: stable fractures of the pelvic ring ( Fig. 2.76).

• A1: Fractures of this type result from spontaneous violent muscle contractions and are most commonly found in adolescent athletes ( Fig. 2.77).

• A2: These are fractures of the iliac wing or fractures of the anterior pelvic ring and are usually due to a lateral compression injury. The CT scan often reveals associated compression fractures of the anterior sacrum. These A2 fractures typically do not become unstable ( Fig. 2.78).

• A3: These are transverse fractures of the inferior end of the sacrum, including the coccyx.

Type B: Fractures with rotational instability but preserved vertical stability ( Fig. 2.79).

• B1: Unilateral external rotation injury with disruption of the symphysis pubis. The trauma impact mostly comes from anterior impact, so that the hemipelvises are forced apart (referred to as an open-book injury). A classic example of this injury is that of a motorcyclist involved in a head-on collision that results in the two halves of the pelvis being separated by the bike’s tank at the time of impact ( Figs. 2.80 and 2.81).

• B2: Unilateral internal rotation injury with disruption of the symphysis pubis and overriding of the anterior pelvic ring. The impact comes from the side, causing the struck side of the pelvic to rotate inward. This results in a fracture of the anterior pelvic ring with internal rotation of the involved half of the pelvis. Here too, the opposing hemipelvises are forced apart, potentially resulting in disruption of the sacroiliac joints anteriorly due to rupture of the anterior sacroiliac ligaments. A typical example is a side-impact collision into the driver-side door of a car.

• B3: Bilateral rotational instability due to bilateral B1 or B2 injuries.

Type C: Fractures with combined rotational and vertical instability. These injuries are commonly caused by being run over or buried. Falls from very great heights can also result in complete disruption of the anterior and posterior pelvic ring:

• C1: This injury is associated with a complete disruption of one hemipelvis, with a stable contralateral side ( Figs. 2.82 and 2.83).

• C2: This is a Type C1 injury of one hemipelvis combined with a Type B injury of the contralateral side.

• C3: This is a bilateral Type C1 injury ( Fig 2.84).

One fracture type not included in the AO classification system is the suicidal jumper’s fracture, in which an axial compression injury results in separation of the spinal column from the pelvis ( Fig. 2.85).

Imaging

Radiography. If the apophysis is already mineralized and sufficiently retracted then it can be readily seen on the radiograph.

US. Separation of the apophyses can be easily evaluated by US in the majority of cases.

MRI. An MRI scan will demonstrate edema of the apophyseal growth plate and the adjacent soft tissues.

Stress-Related Apophyseal Avulsion Fractures

Apophyseal avulsions may result from a single injury or from chronic repetitive microtrauma in athletes. This affects primarily the ischial tuberosity (origin of the hamstrings), the anterior inferior iliac spine (rectus femoris; see Fig. 2.77), anterior superior iliac spine (sartorius and tensor fasciae latae), and less frequently also the pubic bone (adductors). An avulsion fracture of the lesser trochanter (iliopsoas) is also possible, especially in the younger patient. Untreated apophyseal injuries can result in exuberant ossification that may resemble that of a cartilaginous exostosis (osteochondroma) or other bone-forming tumor.

Radiography. Despite the current widespread availability of CT imaging, AP views of the pelvis are still the first study obtained not only for acute assessment but also because they can be used for comparison with postoperative radiographs. Inlet views of the pelvis allow for assessment of AP and rotational malalignment of the pelvic ring, while the outlet view demonstrates any vertical malalignment of the pelvic ring ( Fig. 2.86).

CT. Apart from nondisplaced fractures of the anterior pelvic ring following minimal trauma and typical apophyseal avulsion fractures, CT is typically indicated for all pelvic fractures and multiplanar reconstructions should always be generated. When evaluating the CT, attention should be paid to the course of the fractures as well as to indirect signs of instability such as widening of one or both sacroiliac joints. Small bony avulsions from the caudal sacrum correspond in the majority of cases to avulsion fractures of the sacrotuberous or sacrospinous ligaments and indicate vertical instability.

MRI. MRI has no role in the diagnostic work-up of acute trauma to the bony pelvis but plays an important role in the detection of fatigue fractures (Chapter 2.3.3).

2.3.2 Acetabular Fractures

The anterior and posterior acetabular walls are outward projections of their respective columns.

The AO classification of acetabulum fractures ( Fig. 2.87) is closely based on the classification proposed by Judet and Letournel ( Fig. W2.9), which takes into account the embryonic development of the acetabulum and distinguishes between anterior and posterior columns (see Anatomy above).

• Type A fracture: Only one column is involved; the main part of the joint is intact.

• Type B fracture: Involvement of both columns; one part of the acetabular roof remains attached to the ilium.

• Type C fracture: Complete detachment of the acetabulum from the ilium; both columns are involved.

Radiography. Conventional radiographs are still used to evaluate acetabular fractures despite the availability of CT. In addition to the AP radiograph, iliac and obturator oblique (Judet) views are obtained. Classification is best done using these projections ( Figs. 2.88 and W2.10).

CT. Currently, CT is an integral part of the diagnostic investigation of acetabular fractures. Although fracture classification is more difficult using CT, it provides for detailed assessment of fracture morphology. Small fragments that become entrapped in the joint space are readily evident ( Fig. 2.91). CT is also of crucial importance for optimal pre-operative planning.

2.3.3 Fatigue Fractures of the Pelvis

Fatigue fractures of the pelvis occur predominantly at the pubic rami and the parasymphyseal region. Stress fractures of the sacrum are also found in children, athletes, and pregnant women ( Fig. 2.92); osteoporosis-related insufficiency fractures also occur frequently at this location. Other common sites for an insufficiency fracture include the supra-acetabular region, the ilium, the pubic rami, and the parasymphyseal bone.

Changes due to insufficiency fractures are often very subtle on conventional radiographs and are easily overlooked. CT and especially MRI are very well suited for detecting these fractures. Sacral insufficiency fractures (unilateral or bilateral) typically display vertical fracture lines near to the sacroiliac joint. Horizontal fracture lines are also found in the midsacrum (known as the H-pattern or Honda sign; Fig. 2.93).

2.3.4 Hip Dislocation/Fracture Dislocations of the Hip

In rare cases fracture of the femoral head may occur during dislocation of the hip joint, either in the form of an avulsion fracture of the ligamentum teres or in the form of a shearing fracture related to the posterior acetabular rim. Such fractures of the femoral head are classified according to Pipkin ( Fig. 2.94).

CT is essential for assessing Pipkin fractures and provides the only method for correctly assessing the size of the sheared fragment and of the defect within the femoral head ( Fig. W2.12).

2.3.5 Pubalgia (Osteitis Pubis)

Anatomy. See Chapter 2.3.5 including Fig. W2.13.

Pathology. Osteitis (symphysitis) pubis is a chronic overuse injury of the symphysis and the adjacent pubic rami. This stress reaction may also be associated with adductor pathology. It is often the cause of groin pain in athletes and affects football players in particular.

Radiography/CT. The appearance depends on the chronicity of the stress reaction. Initially, resorptive changes may predominate, in which case the joint space is widened ( Figs. 2.95a and 2.96). In more chronic cases, subchondral sclerosis and osteophytes predominate, often with joint space narrowing ( Fig. 2.95b).

MRI. MRI allows differentiation of osteitis pubis from adductor injuries and other causes of groin pain.

Findings in osteitis pubis:

• Increased signal intensity on water-sensitive sequences or enhancement (after IV administration of gadolinium) in the bones adjacent to the symphysis and in the symphyseal joint space ( Fig. 2.97).

• Concomitant involvement of the adjacent adductor entheses (in ~ 60% of cases; see Fig. 2.97).

• Osteophytes.

• Cysts or geodes (in ~ 80% of cases; Fig. 2.98)

• Erosions at the insertions of the pubic ligament.

• So-called secondary cleft sign (a bright line between bone and the joint space; Fig. 2.99).

US. Ultrasound is helpful for injuries of the nearby tendon insertions of the rectus abdominis and the adductors but is unable to demonstrate stress changes within the bones.

DD.

Infections. In cases of infection, MRI should be used to detect intra-articular or para-articular abscesses ( Fig. 2.100). Laboratory results should also be examined.

Rheumatic disorders. Seronegative spondylarthropathies can also affect the symphysis. The underlying condition is almost always known, so there are rarely any differential diagnostic difficulties.

Inguinal hernia. A sound physical examination and, in some cases, the use of ultrasound should allow for accurate diagnosis.

Tendinopathy of the adductors or rectus abdominis. The use of ultrasound or MRI will provide an accurate diagnosis ( Fig. 2.101).

2.4 Shoulder Joint

2.4.1 Anatomy, Variants, and Technique

Anatomy. See Chapter 2.4.1 including Figs. W2.13– W2.19.

Variants

The shape of the acromion demonstrates considerable variation. The variants reported by Bigliani and Gagey ( Fig. 2.102) refer to the differences in morphology of the acromion in the sagittal plane, but this provides an incomplete definition of the geometry of the subacromial space because of additional variation in acromial morphology in the coronal plane.

Os acromiale ( Fig. 2.103) refers to a persistent ossification center of the anterior acromion. The finding occurs bilaterally in about 60% of cases and must not be mistaken for a fracture of the acromion. It should be kept in mind that fusion of the acromial ossification center is not complete until relatively late (between 21 and 25 years of age).

Anatomically, the glenoid labrum is a highly variable structure. Its cross-sectional shape ranges from triangular to round and is of variable size. A sublabral foramen ( Figs. 2.104 and 2.105) is a relatively common normal variant (incidence: 7–12% of individuals). This refers to a lack of attachment of the labrum to the anterosuperior part at the glenoid (at the 1 to 3 o’clock position). A “Buford complex” refers to absence of the labrum in this region associated with a thickened, cordlike middle glenohumeral ligament, which may rarely insert on the long biceps tendon. This anomaly is less common, with an incidence of 1.5 to 2% (see Fig. 2.104). The anteroinferior labrum is normal in both of these variants.

The anatomy of the biceps tendon anchor varies considerably. A firm attachment of the superior labrum to the glenoid margin is evident in only 30% of individuals ( Fig. 2.106a). A sublabral cleft of variable depth (2–10 mm), lined with a synovial membrane, is commonly found and known as a sublabral recess ( Fig. 2.106b). In the presence of a deep recess, the superior labrum may be meniscoid and hypermobile. A sublabral recess may extend anteriorly into a sublabral foramen.

• Suspected SLAP lesion (superior labral anterior-to-posterior lesion; see relevant part of Chapter 2.4.6).

• Diagnostic work-up for shoulder pain in competitive athletes.

2.4.2 Impingement

Impingement syndromes are among the most common types of pathology of the shoulder joint. A distinction is made between primary and secondary extrinsic, and secondary intrinsic impingement syndromes ( Table 2.2).

Primary Extrinsic Impingement

Subacromial Impingement

Pathology. Primary extrinsic impingement (i.e., outlet impingement) is due to narrowing of the subacromial space. Impingement of the supraspinatus tendon and the subacromial bursa between the anterior acromion and the head of the humerus causes chronic bursitis and tendinopathy of the supraspinatus. A tendon tear may develop over time. Affected patients are typically older than 40 years of age and do not present with shoulder instability.

Predisposing factors for subacromial impingement include a Bigliani Type 3 acromion (see Fig. 2.102), subacromial osteophytes, a laterally downsloping acromion, a thickened coracoacromial ligament, and an (unstable) os acromiale. Osteoarthritis of the acromioclavicular joint with marked osteophytes and hypertrophy of the rotator cuff are rare causes.

Clinical presentation. Classic symptoms are nocturnal pain, pain on elevation of the arm between 60 and 120° (“painful arc”), shoulder stiffness, and weakness.

Radiography. Assessment of acromial morphology is best accomplished on an outlet view (SST [supraspinatus tendon] view, Neer view). Subacromial osteophytes are found at the anterior margin of the acromion in the region of the insertion of the coracoacromial ligament; strictly speaking, therefore, they are enthesophytes. Narrowing of the acromiohumeral interval to less than 7 mm is considered pathologic and is suggestive of a rotator cuff tear ( Fig. 2.107). Tendon calcification is not part of the subacromial impingement syndrome, but instead indicates calcific tendinitis secondary to calcium hydroxyapatite deposition disease (Chapter 10.9.3).

MRI. Subacromial impingement is a clinical diagnosis. MRI ( Figs. 2.108 and 2.109) may demonstrate a typical constellation of findings but is unable to establish the diagnosis. The task of MRI is to define the stage of disease, especially with regard to rotator cuff integrity. Fluid-sensitive images may demonstrate increased fluid content and/or thickening of the wall of the subacromial bursa, which is often the only finding in early stages of the disorder. Over time, tendinopathy of the supraspinatus develops (Chapter 2.4.3). Thickening of the tendon will further narrow the subacromial space. Rotator cuff tears typically involve the anterior fibers of the supraspinatus tendon from where they can progress further. The morphology of the acromion can be well appreciated on oblique sagittal and oblique coronal views, while an os acromiale is best seen on transverse slices. Commonly reported, but less meaningful, findings include thickening or a convex course of the coracoacromial ligament and the absence of the subacromial fat pad.

US. Ultrasound demonstrates thickening of the wall of the subacromial/subdeltoid bursa, which may be partially fluid-filled. A recognizable sign of subacromial impingement during abduction of the arm is a “ballooning” of the lateral part of the subdeltoid bursa, which results from fluid being pressed out of the medial part of the bursa as the bursa glides beneath the acromion. Signs of tendinopathy are thickening of the tendon, decreased and somewhat heterogeneous echogenicity, and loss of the normal fibrillar structure of the tendon; comparison with the contralateral side is sometimes helpful. Identification of tendinopathy, however, does not prove the presence of a subacromial impingement syndrome.

Table 2.2 Classification of impingement at the shoulder

Subcoracoid Impingement

MRI. MRI findings of instability impingement do not differ from those of primary subacromial impingement with respect to the changes of the subacromial space (see Subacromial Impingement at the beginning of Chapter 2.4.2).

Secondary Intrinsic Impingement

See also Chapter 2.4.5.

2.4.3 Rotator Cuff Pathology and Biceps Tendinopathy

A basic distinction is made between tendinopathy, partial-thickness and full-thickness tears. With tendinopathy only degenerative changes of the tendon are present, without macroscopically evident interruption of continuity. Partial-thickness tears involve only a portion of the tendon, whereas full-thickness tears extend across the entire thickness of the tendon, at least at one site ( Fig. 2.110). Full-thickness tears are therefore “transtendinous” and result in a communication between the joint cavity and the subacromial bursa.

Table 2.3 Variants of partial lesions of the rotator cuff

These are classified according to their location as articular-sided (most common type), bursal-sided, or intratendinous. In recent years, several variants of partial tears have been reported ( Table 2.3; see also Fig. 2.110). The depth of articular- or bursal-sided partial tears may be classified according to Ellman ( Table W2.1 in Chapter 2.4.3).

Full-thickness Tears

Full-thickness tears typically result from progression of a partial-thickness tear over time. A distinction is made between small (≤ 1 cm), intermediate (1–3 cm), large (3–5 cm), and massive tears (larger than 5 cm in the sagittal plane). Larger defects may be associated with retraction of the proximal tendon stump in a medial direction. The extent of the retraction may be classified according to Patte ( Fig. 2.111).

Tears of the Subscapularis Tendon

The subscapularis tendon is often involved in cases of extensive degenerative rotator cuff lesions. Isolated tears are less common and occur, for example, after traumatic anterior shoulder dislocation. Because defects of the subscapularis tendon typically progress in a cranial to caudal direction, Fox and Romeo have proposed a specific classification system ( Table 2.4).

Radiography. It is not possible to diagnose focal lesions of the rotator cuff on radiographs. Cranial migration of the humeral head with an acromiohumeral distance of less than 7 mm indicates a large defect of the supraspinatus and infraspinatus tendons. The term “defect arthropathy” ( Fig. 2.112) describes contact of the humeral head and acromion resulting in osseous remodeling and degenerative cyst formation as well as glenohumeral osteoarthritis in long-standing, extensive rotator cuff tears.

MRI. Tendinopathy displays increased signal intensity of the tendon on sequences with short echo times (T1W, PDW) and less-intense signal elevation on sequences with long echo times ( Fig. 2.113). The affected tendon can appear thickened but does not demonstrate any fiber discontinuity. Magic-angle artifacts may result in a similar appearance but are not usually a problem if intermediate-weighted pulse sequences (with echo times > 35 milliseconds) are used.

A tendon tear is diagnosed when fluidlike signal intensity is seen within the tendon on intermediate-weighted or T2W images. In a partial-thickness tear ( Fig. 2.114a), the alteration affects only a part of the tendon thickness, whereas the entire thickness of the tendon is involved in a full-thickness tear ( Fig. 2.114b). Apart from signal characteristics, attention should also be paid to tendon morphology, i.e., to evidence of interruption in the course of the tendon fibers. A limitation of conventional MRI lies in its difficulty in differentiating tendinopathy from a partial-thickness tear. While the sensitivity for detecting partial tears is therefore relatively low, the accuracy in diagnosing of full-thickness tears is high.

With the aid of MR arthrography the sensitivity increases to over 80% for articular-sided partial-thickness tears. An additional diagnostic criterion for diagnosing a partial-thickness tear rather than tendinopathy is the leakage of contrast into the substance of the tendon ( Figs. 2.115 and 2.116). With a full-thickness tear, contrast passes through the transtendinous defect into the subacromial bursa (see Fig. 2.114b).

Rotator cuff tears may result in atrophy and, over time, irreversible fatty degeneration of the affected muscles. Assessment of the rotator cuff muscles can be made using the semiquantitative Goutallier classification system ( Table 2.5). The most lateral image of an oblique sagittal T1W or T2W sequence (obtained without fat saturation!) where the scapula is seen to form a Y shape is used as a reference level ( Fig. 2.117).

Table 2.4 Fox and Romeo classification of tears of the subscapularis tendon

Table 2.5 Semiquantitative classification of fatty degeneration of muscles according to Goutallier

US. In experienced hands, ultrasound can provide results comparable with those of conventional MRI with regard to the recognition of tendon defects. Differentiation between tendinopathy and a partial-thickness tear remains difficult, however. Furthermore, it should be borne in mind that anisotropy of tendon fibers can create the impression of a defect. To avoid this, any suspicious finding should be examined from several aspects with different probe angles. Apart from direct signs of tear, such as interruption of tendon fibers and release of fluid into the tendon or bursa ( Fig. 2.118a), indirect signs should also be looked for. A focal impression (“dent”) in the convexity of the tendon surface or a circumscribed double contour over the surface area of the humeral head ( Fig. 2.118b), corresponding to hyaline articular cartilage, is encountered only with a tear, not with tendinopathy. Limitations of ultrasound include only moderate reliability in evaluating the state of muscles and its low sensitivity for concomitant pathologic states (e.g., labral pathology).

CT. CT arthrography using multidetector technology with image reconstructions in all three anatomical planes may be used as a “back-up procedure,” for example when there are contraindications against an MRI examination. Transtendinous defects and articular surface partial tears of the supraspinatus and infraspinatus tendons are detectable with high sensitivity and specificity ( Fig. 2.119). This technique is limited, however, by low sensitivity for intratendinous and bursal-sided lesions and for many lesions of the subscapularis tendon. The Goutallier classification system can be used because it was originally developed for CT scanning.

DD. There is a differential diagnosis for the clinical symptoms of a rotator cuff tear.

With the development of acute symptoms, a distinction must be made between isolated subacromial bursitis without rotator cuff defect, calcific tendinitis secondary to calcium hydroxyapatite deposition disease, and an avulsion fracture of the greater tuberosity. Suprascapular nerve palsy secondary to entrapment neuropathy or a postinfectious neuritis (Parsonage–Turner syndrome) is a relatively rare differential diagnosis. Other pathologies that can have a clinical presentation similar to that of a rotator cuff tear include SLAP lesions (Chapter 2.4.6) and traumatic osteolysis of the distal clavicle (Chapter 2.5.6).

Biceps Tendinopathy

Pathology. Tendinopathy of the long head of the biceps tendon is often an associated condition in patients with subacromial impingement and lesions of the rotator cuff as well as secondary to instability of the tendon (pulley lesion; Chapter 2.4.4). However, biceps tendinopathy can also develop as an isolated overuse injury in athletes involved in overhead and throwing activites. Anterior shoulder pain is the cardinal clinical symptom. Partial-thickness tendon tears and eventually full-thickness tears can develop from initial tendinopathy, which typically involves the horizontal (intra-articular) part of the tendon.

MRI. MRI signs of biceps tendinopathy are thickening and irregular contours of the tendon and increased signal intensity on sequences with short echo times. These alterations are best identified on oblique sagittal images ( Fig. 2.120). Partial tears can manifest as an increase in caliber and signal intensity of the tendon on T1W and T2W sequences or as attenuation of the tendon. Discontinuity or complete absence of the horizontal portion of the tendon are signs of a full-thickness tear ( Fig. 2.121).

US. It is not possible to demonstrate the proximal insertion of the biceps tendon at the glenoid by ultrasound, but its more lateral intra-articular segment can be well visualized. Difficulties can arise in obese patients. Tendinopathy of the biceps tendon with thickening, heterogeneous echogenicity and increased vascularization may be detected with ultrasound, as may partial or full-thickness tears. An “empty” intertubercular groove requires differentiation between a tear and a dislocation of the long biceps tendon out of its groove (cf. Fig. 2.125). This is possible by tracing the tendon from its myotendinous junction in a cranial direction.

2.4.4 Pathology of the Rotator Interval

Injuries of the superior glenohumeral ligament, also termed pulley lesions, are of more clinical significance and can occur in isolation or in combination with tears of the supraspinatus tendon and/or subscapularis tendon, resulting in instability of the long biceps tendon. Habermeyer has described four types of pulley lesions ( Fig. 2.122 and Table W2.2); Type 1 (frequency: 29–74%) refers to an isolated tear of the superior glenohumeral ligament.

MRI. Rotator interval lesions are well demonstrated only with the aid of MR arthrography. Pulley lesions can be diagnosed on oblique sagittal MR arthrographic images with a sensitivity and specificity of more than 80%. Reliable signs are inferior displacement of the long head of the biceps tendon onto the subscapularis tendon within the rotator interval (displacement sign) and discontinuity of the superior glenohumeral ligament ( Fig. 2.123). This is almost always associated with tendinosis of the biceps tendon. Medial displacement of the biceps tendon, recognizable on transverse sections, is usually only encountered in conjunction with a simultaneous lesion of the subscapularis tendon, but not with an isolated tear of the superior glenohumeral ligament. With a lesion of the superior glenohumeral ligament and a partial defect of the subscapularis tendon, the biceps tendon can dislocate into the defect, i.e., deep to the coracohumeral ligament. Intra-articular dislocation can occur with a full-thickness tear of the subscapularis tendon ( Fig. 2.124). Extracapsular dislocations of the biceps tendon (ventral to the subscapularis tendon) associated with a tear of the coracohumeral ligament are very rare. Capsular tears can occasionally be identified as contrast leakage in the region of the interval into the subacromial/subdeltoid bursa.

US. Instability of the long biceps tendon can be recognized using ultrasound when it is seen to subluxate or dislocate out of the intertubercular sulcus. This is best achieved with a dynamic examination during forced external rotation ( Fig. 2.125).

2.4.5 Shoulder Instability

Bankart lesions and Perthes lesions represent approximately 90% of the injuries that occur secondarily to traumatic anterior first-time acute dislocation. In the classic Bankart lesion, the anteroinferior labrum, together with the inferior glenohumeral ligament, is completely detached from osseous glenoid ( Fig. 2.126). Because there is also an additional disruption of the scapular periosteum, the labrum is usually displaced from its normal anatomical position, and may be “floating” freely in the anterior joint space.

A Perthes lesion is distinguished from a Bankart lesion by the fact that although an avulsion of the labrum off the glenoid exists, it is still attached to the glenoid via scapular periosteum, which is stripped anteromedially but not disrupted. The unstable labrum often remains in a relatively normal position and the tear can be masked by scar tissue and re-synovialization. Fluid may be seen tracking between the labrum and glenoid or beneath the periosteum and is sometimes more readily apparent in the ABER position, i.e., with the inferior glenohumeral ligament under tension ( Fig. 2.127).

ALPSA Lesion

An ALPSA lesion (anterior labroligamentous periosteal sleeve avulsion) is found as a chronic variant of a Perthes lesion, usually after multiple anterior shoulder dislocations (chronic instability). With this type of lesion, the anteroinferior labroligamentous complex becomes detached from the glenoid rim and is displaced medially, where it scars over along with its periosteal attachment to the scapular neck. Although there is no actual ligament disruption, incompetence of the inferior glenohumeral ligament develops due to the abnormal labral position. The result is shoulder instability. Characteristic signs of an ALPSA lesion are medially and caudally displaced labral tissue ( Fig. 2.128) which appears larger due to a proliferation of associated scar tissue along the scapular neck, and a crease, or cleft, between the glenoid and the labrum (cleft sign; see Fig. 2.128b).

Bony Bankart Lesion

The bony Bankart lesion is an avulsion fracture in which the anteroinferior labroligamentous complex is detached from the glenoid together with a bony fragment of variable size ( Fig. 2.129). While small bony fragments may be regarded as therapeutically and prognostically irrelevant, larger fragments require refixation or reconstruction of the glenoid.

HAGL Lesion

In the very rare HAGL lesion (humeral avulsion of glenohumeral ligament), the anteroinferior labroligamentous complex is not disrupted at its glenoid attachment but is at the humerus ( Fig. 2.130). The inferior glenohumeral ligament may be avulsed directly or together with a bone fragment (~ 20% of cases) from its insertion on the humeral neck. The anterior capsule of the axillary recess no longer appears U-shaped on coronal images but rather is J-shaped due to the lateral discontinuity of the inferior glenohumeral ligament (“Jsign”). Acute HAGL lesions may be associated with fluid leakage and/or a hematoma at the insertion site of the inferior glenohumeral ligament.

Hill–Sachs Defect/Fracture

Hill–Sachs defects are detectable after traumatic first-time acute dislocations in 47 to 100% of cases. This lesion may or may not be present in patients who have sustained a significant anterior labroligamentous injury. Except for very large lesions, Hill–Sachs defects are of little clinical relevance, but detection of such a lesion indicates a previous anterior shoulder dislocation. On axial images, a Hill–Sachs defect is always located posterolaterally at or above the level of the coracoid. Acute lesions are usually surrounded by areas of bone contusion ( Fig. 2.131).

Radiography. It is hardly possible to miss an acute anteroinferior shoulder dislocation on conventional radiographs ( Fig. 2.132). Follow-up films after reduction serve to exclude any associated bony injuries (osseous Bankart lesion, fracture of the greater tuberosity). Smaller bony avulsions from the anteroinferior glenoid rim are usually not visible on standard projection views. If a conventional radiological depiction is requested, then an osseous Bankart lesion is best seen on a Westpoint or axillary view, whereas a Hill–Sachs defect is best displayed on an AP radiograph in internal rotation or on a Stryker view.

CT/CT arthrography. CT is the modality of choice for demonstrating the extent of an acute glenoid fracture or chronic glenoid defect resulting from progressive bone loss after multiple dislocations; quantification of the size of the bony abnormality is best accomplished on oblique sagittal image reconstructions. Hill–Sachs defects are also readily detected with CT. The results of CT arthrography are comparable to those of MR arthrography with respect to the assessment of labroligamentous injuries. The advantages of CT arthrography lie in the recognition of bony Bankart lesions and in diagnosing articular cartilage lesions. Its disadvantages include its limited ability to assess soft tissue structures and its use of ionizing radiation (especially important in young patients).

MRI/MR arthrography. Conventional MRI is most suitable for demonstrating injuries immediately after the event, i.e., within a few days after the acute dislocation, since an associated joint effusion or hemarthrosis will act as a natural contrast medium and allow for more accurate assessment of the labrocapsular structures. Direct MR arthrography is the modality of choice, with a sensitivity of more than 88% and a specificity of more than 90% for the detection of labroligamentous lesions. Its accuracy in characterizing the type of injury as compared with arthroscopic findings is 84%. This technique also allows for reliable detection of associated injuries, such as SLAP lesions (Chapter 2.4.6).

DD. Differentiation of a labroligamentous injury from an anatomical variant of the glenoid labrum is relatively easy. An abnormality seen exclusively within the anterosuperior quadrant of the labrum (a sublabral foramen or a Buford complex) (Chapter 2.4.1) it is always located in the anterosuperior quadrant, whereas most true labroligamentous lesions typically involve the anteroinferior quadrant, or at least begin there.

Traumatic Posterior Instability

Radiography. Radiographs are diagnostic for acute or locked posterior shoulder dislocation. In a “true” AP projection, overlapping of the contours of the internally rotated head of the humerus and the joint socket is evident ( Fig. 2.133). There is often a line of density running parallel to the medial contour of the humeral head (trough line; see Fig. 2.133), corresponding to the lateral margin of the “reverse” Hill–Sachs defect (trough sign). In questionable cases, a radiograph in a second projection (axillary, transscapular or transthoracic) confirms the posterior dislocation of the humeral head.

CT. CT accurately shows the size and orientation of “reverse” Hill–Sachs defects as well as additional bony injuries of the posterior glenoid rim and whether the dislocated humeral head is “locked” along the posterior glenoid rim ( Fig. 2.134).

MRI. As with anterior instability, a conventional MRI examination is most useful immediately after the dislocation, whereas in the more chronic setting, MR arthrography should be considered ( Fig. 2.135). In addition to damage to the posterior labroligamentous complex, patients with posterior shoulder instability are not uncommonly found to have concomitant lesions of the rotator cuff.

Atraumatic Instability

Pathology. Atraumatic shoulder instability is typically multidirectional, occurs bilaterally, and often affects patients with generalized hyperlaxity of the joints (congenital hypermobility syndrome). Multiple subluxations or dislocations are typical, and can also occasionally be produced voluntarily. Apart from a capacious joint capsule, intra-articular findings are commonly absent. However, in athletes with multidirectional shoulder instability, labral and rotator cuff lesions are not uncommonly present.

MRI. With multidirectional shoulder instability, the primary role of MR arthrography is to exclude the presence of associated intra-articular pathology. Frequently a stretching and redundancy of the capsule can be readily recognized, especially in the region of the rotator interval. A glenohumeral ligament that does not appear to be stretched on images in the ABER position is also suggestive of capsular redundancy.

Microinstability

Pathology. Microinstability (also known as “functional instability” or “microtraumatic instability”) represents a subclinical form of shoulder instability that develops mainly in athletes secondarily to chronic overuse with repetitive injury to the capsular structures. These forms of instability are most commonly found in sports that involve abduction and external rotation of the shoulder (overhead sports). These patients typically present with pain and reduced motion of the shoulder rather than overt subluxation or dislocation events. Secondary damage to articular structures may develop, especially to the glenoid labrum and rotator cuff.

Posterosuperior glenoid impingement is a typical intrinsic form of impingement that occurs in the overhead athlete due to microinstability with abnormal anterior translation of the humeral head during the cocking phase. It most commonly manifests clinically as acute or chronic posterior shoulder pain. With posterosuperior glenoid impingement, there is repetitive pathologic contact between the joint surface of the rotator cuff (especially the posterior fibers of the supraspinatus and anterior fibers of the infraspinatus tendons) and the posterior superior glenoid rim during external rotation and abduction. These tendons may also become entrapped between the glenoid and greater tubercle, resulting in injuries to the posterior cuff and posterosuperior glenoid labrum.

Anterosuperior impingement is much less common and involves the subscapularis tendon and pulley system when the arm is brought into internal rotation and adduction (followthrough phase of throwing or striking movements) during which these structures become entrapped between the anterior superior glenoid rim and the humeral head. The most common clinical symptom is anterior shoulder pain.

MRI. MR arthrography is the most useful imaging technique for evaluating athletes presenting with shoulder problems. A variety of often subtle articular lesions can result from microinstability: Stretching of the joint capsule, an array of labral pathology (degeneration, tear, avulsion, SLAP lesion), or rotator cuff lesions may occur in isolation or in combination ( Fig. 2.136).

A characteristic pattern of “kissing lesions” is found in patients with posterosuperior glenoid impingement (see Fig. 2.136c). MR arthrography typically demonstrates an articular-sided partial-thickness tear of the posterior fibers of the supraspinatus tendon and/or anterior fibers of the infraspinatus tendon, combined with a lesion of the posterosuperior glenoid labrum. With excessive contact, bony alterations such as bone marrow edema, cyst formation, and sclerotic changes in the greater tubercle and superior glenoid may also be seen. Lesions of the anterior joint capsule are evident on axial views and may be accentuated on views obtained in the ABER position and vary from degenerative changes to elongation and tear of the inferior glenohumeral ligament.

In cases of anterosuperior glenoid impingement, MR arthrography can demonstrate the pulley lesion with discontinuity of the superior glenohumeral ligament and the sequelae of the associated instability of the biceps tendon. Lesions of the subscapularis tendon typically start along the articular surface of the superior part of the tendon.

2.4.6 Other Labral Pathology

The classification system of Snyder distinguishes four different types of SLAP lesions ( Table 2.6 and Fig. 2.137). Whereas the Type 1 SLAP lesion, as a purely degenerative alteration, is of hardly any clinical relevance, Type 2 (the most common type) and Type 4 lesions often cause instability of the biceps anchor and are an indication for superior labral repair or biceps tenodesis. The biceps tendon is stable in the Type 3 SLAP lesion; treatment therefore involves only resection of the bucket-handle tear. Various other reported lesions mostly represent combination injuries of a Type 2 SLAP lesion plus damage to the labrum, the middle glenohumeral ligament or the rotator cuff. This extended classification is not typically used, however.

MRI. Conventional MRI has only a low sensitivity for the detection of SLAP lesions and, as a result, MR arthrography is the method of choice; it exhibits high sensitivity (82–92%) and specificity (80–99%) in this regard ( Fig. 2.138).

Type 1 SLAP lesions manifest as contour irregularities of the superior labrum, but are only rarely detectable. With a Type 2 lesion, leakage of contrast medium into the superior labrum and the biceps/labral anchor is observed. A cleft of contrast extending laterally into the substance of the labrum is a very predictive sign of a true SLAP tear since a Type 2 SLAP tear can be very difficult to differentiate from a sublabral recess. However, the normal recess is typically oriented in a medial direction (Chapter 2.4.1). Other findings suggesting a true Type 2 SLAP lesion are irregular labral margins and a wide separation between the labrum and glenoid. Types 3 and 4 are bucket-handle tears, in which the torn fragment may be displaced caudally into the joint to a greater or lesser degree. In Type 3, the fragment typically appears triangular on coronal views and separated from the intact biceps tendon. In Type 4 the bucket-handle fragment includes both the superior labrum and parts of the biceps tendon.

CT/Arthrography. CT arthrography is considered equivalent to MR arthrography in diagnosing SLAP lesions.

DD. Differentiation between a Type 2 SLAP lesion and a sublabral recess (Chapter 2.4.1 and Fig. 2.137) may be difficult, if not impossible, but the orientation of the “cleft” and its morphology should provide helpful clues for accurate diagnosis.

GLAD Lesion

Pathology. The GLAD lesion (glenolabral articular disruption) involves a combination of a focal articular cartilage defect along the anteroinferior glenoid, typically with a subtle tear of the adjacent labrum. It is not typically associated with glenohumeral instability. The cause is presumed to be an eccentric impaction of the head of the humerus against the glenoid during a fall on the outstretched arm or on the shoulder. A posterior variant of the GLAD lesion has also been reported.

MRI. MR arthrography demonstrates a tear near the base of the nondisplaced labrum and a cartilaginous lesion involving the adjacent anteroinferior or posteroinferior quadrant of the glenoid ( Fig. 2.139). There is no injury to the inferior glenohumeral ligament. The extent of glenoid cartilage damage varies.

Table 2.6 Snyder classification of SLAP lesions

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