Radiologic Aspects Of Orthopedic Diseases

Chapter 16 Radiologic Aspects of Orthopedic Diseases



This chapter contains a radiologist’s viewpoints and suggestions regarding the interpretation of bone roentgenograms. It is hoped this will serve as a useful and practical guide for the busy physician. Principles concerning roentgenographic positioning, anatomy, and pathology are presented by using a regional anatomic approach. Additionally, the musculoskeletal applications of specialized radiologic modalities are discussed. This includes comments on nuclear medicine procedures, diagnostic ultrasound, arthrography, and angiography. Importantly, the imaging technologies of computed tomography (CT) and magnetic resonance imaging (MRI) as they pertain to the evaluation of orthopedic problems are detailed.



General Considerations of Roentgenographic Bone Anatomy


Before beginning a detailed discussion of regional roentgenographic anatomy and pathology, a consideration of pertinent radiologic bone anatomy is important. A bone can be evaluated according to its various components (Fig. 16-1).










Analytic Approach to Bone Changes



GENERAL CONSIDERATIONS


This section discusses some basic fundamentals and principles related to bone roentgenograms, rather than going into a great deal of confusing anatomic and pathologic detail. The first and foremost rule is that every roentgenogram is abnormal until it is proved, after thorough examination, that everything is normal. It may not work all of the time, but this approach encourages as complete a search of the film as possible. This results in two important objectives. First, it eliminates the method of instantaneous pattern recognition. Second, it prods the physician to search for even the slightest, most subtle change in bone roentgenographic patterns. It is important to avoid tunnel vision; one should look at the “whole picture,” from the corners of the film to the center. This involves separate evaluations of the soft tissues, joints, bone density, architecture, and trabecular patterns. Scrutinizing the medullary cavity and spongiosa, as well as the cortex, periosteum, and endosteum, is also necessary to get the overall picture.


In other words, an analytic approach should be attempted by evaluating each specific feature of bone. Each detail must be visualized separately. An obvious fracture catches one’s attention, and the tendency is to forget the remainder of the picture, possibly missing an associated but unsuspected dislocation or even an early destructive tumor.


Taking two views of a bone at right angles is an important law in radiology. Diagnostic interpretations should never be made on the basis of one view. There should be no hesitation to obtain additional projections of the suspicious area if there is any suggestion that something is wrong. Comparative films of the opposite side are also often helpful, especially in younger patients whose growth centers cause more than enough confusion. And if the roentgenograms remain normal to the eye but clinical suspicion persists, the patient must return in 7 to 10 days for repeated films, because it is not uncommon for a stress fracture, radial head fracture, or early osteomyelitis to have delayed appearances roentgenographically.


Once a bone lesion is discovered on radiographic film, a differential diagnosis can be formed. At first, the spectrum of possibilities might be quite broad, but by correlating historical, physical, and laboratory findings with the roentgenographic discovery, the spectrum can be narrowed to a few diseases and will, in most instances, lead to the correct diagnosis.


To permit the most accurate diagnosis, the differential list should be based on certain specific bone responses that are most characteristic of the disease process. There are various distinctive visible reactions that bone may have to singular disease entities, such as the pattern of bone destruction or production, the type of periosteal reaction, and soft tissue involvement, if any.


Unfortunately, there are more diseases affecting bone than there are responses that bone can create. Consequently, there are more roentgenographic similarities than differences among the various bony lesions. For example, the periosteal reaction usually associated with Ewing’s sarcoma, characteristically described as “onion skin,” quite often occurs with osteomyelitis.


Conversely, there are specific disease processes that produce more than one kind of predictable bone reaction. Such is the case with osteomyelitis, whose periosteal response can appear benign but can also mimic malignant changes.


Any office or clinic that performs diagnostic radiographic film studies should have appropriate references available for proper positioning of the patient. Several technical books may be found to assist the nurse or technician when examining the various skeletal regions. A three-volume set by Ballinger, Merrill’s Atlas of Roentgenographic Positions (2003), is highly recommended.



SPECIFIC PARAMETERS


Certain specific parameters of bone need careful attention. In the process of evaluating these, using a systematic approach can lead to a logical conclusion. Among the criteria to be analyzed are an increase or decrease in bone density, alterations in osseous texture (trabecular pattern), periosteal reactions, and the conditions of the cortex, endosteum, and medullary spongiosa. If any changes of these are observed, then the abnormality should be studied in terms of its size and configuration and the sharpness of its margins (transition zone). The specific bone involved and the position of the lesion within that bone (epiphysis, metaphysis, or diaphysis) should also be noted. For example, leukemia, metastatic neuroblastoma, a benign simple cyst, and Brodie’s abscess have a predilection for the metaphysis, whereas a chondroblastoma typically involves the epiphysis.


This is a simple, general outline, and many more particulars come into play. By developing this type of approach, the many clues offered will help to determine the nature of the pathologic process and place the lesion into a certain category (for example, benign, malignant, infectious, traumatic, or metabolic). Table 16-1 lists some of the specific characteristics of different bone lesions.


Table 16-1 General Characteristics of Different Bone Lesions













































Characteristics of benign bone lesions
Sclerotic margins (narrow transition zone)
Homogeneous periosteal reaction
Expansion of an intact cortex
Characteristics of solitary malignant bone lesions
Permeative or moth-eaten destruction (wide transition zone)
Irregular, sometimes spiculated periosteal reaction
Preferential metaphyseal location
Extraosseous extension with soft tissue mass and occasional fluffy calcifications
Characteristics of metastatic lesions
Absence of periosteal reaction
Moth-eaten destruction of medulla and cortex
Preferential diaphyseal location
Pathologic fractures
Multiple bone involvement
Characteristics of infection
Often irregular periosteal reaction, no spiculation
Bone destruction variable
Diaphyseal involvement, often involving long segments
Destruction of adjacent cartilage, crossing joints (majority of malignant neoplasms lack this ability)
Sequestration and involucrum formation

Two parameters require more expanded discussion: patterns of bone destruction and periosteal reaction.



PATTERNS OF BONE DESTRUCTION


Three roentgenographic patterns of bone destruction have been described, according to Lodwick: geographic, moth-eaten, and permeative.





Regardless of the type of osseous resorption that is taking place, as much as 50% of the bone must be destroyed before it becomes evident roentgenographically. Radionuclide bone scans constitute a much more sensitive examination for determining the presence of bone replacement by the tumor or infection. The more advanced nuclear technology of single proton emission computed tomography (SPECT) imaging further enhances this lesion detection sensitivity. In one comparative study, the accuracy of isotope imaging with technetium 99m phosphate complexes for skeletal lesion detection was 98%, as compared with 28% for standard roentgenography (Siberstein, Saenger, Tofe, 1973). Because of this fact, the use of skeletal roentgenographic surveys has declined in favor of nuclear scans. Nevertheless, although the sensitivity of scanning is high, its specificity is low, and therefore roentgenographic studies of the abnormal isotope areas are mandatory. CT and MRI can be a helpful adjunct in the determination of the presence of marrow replacement by metastatic lesions.



TYPES OF PERIOSTEAL REACTIONS


When the outer periosteal membrane of bone is irritated, its constituent osteoblastic cells react by producing new bone. This new bone can take on either a solid or an interrupted appearance, and the specific form can assist in identifying the inciting cause (Table 16-2). Solid periosteal reactions are usually indicative of a benign process. The new bone is consistently uniform in density. As seen in Table 16-2, the thickness and marginal characteristics vary according to the precipitating factor.


Table 16-2 Roentgenographic Types of Periosteal Reactions*








































Types Examples
Solid periosteal reaction
Thin Eosinophilic granuloma, osteoid osteoma
Thin undulating Hypertrophic pulmonary osteoarthropathy
Dense undulating Vascular
Dense elliptical (with destruction) osteoid osteoma  
Cloaking Long-standing malignancy
Chronic infection  
Interrupted periosteal reaction
Perpendicular (spiculated or sunburst) Osteosarcoma, Ewing’s sarcoma, infection
Lamellated (onion skin) Osteosarcoma, Ewing’s sarcoma, infection
Amorphous Malignant tumors
Codman’s triangle Malignant tumors, infection, hemorrhage

* From Edeiken J, Hodes PJH: Roentgen diagnosis of diseases of bone, Baltimore, 1967, Williams & Wilkins. Used by permission.


The interrupted forms of periosteal reactions are more commonly found in malignant disease, although benign lesions such as infection are occasionally responsible. The classic spiculated or sunburst pattern of osteogenic sarcoma and the lamellated or onion skin, periosteal reaction of Ewing’s sarcoma come under this heading (see Table 16-2).


Of the various types of periosteal reactions, Codman’s triangle is of special interest. This form is produced by a lifting of the periosteum, which causes a break in its continuity and forms an angle. Thought to be pathognomonic of malignancy at one time, it is now known to develop in benign diseases as well. The sign can be induced by underlying infiltrating tumor cells, pus, or hemorrhage.


Another interesting periosteal condition is hypertrophic pulmonary osteoarthropathy. The uniform, thin, but solid undulating new bone, often associated with bone pain, is a relatively infrequent roentgenographic finding in individuals suffering from benign and malignant thoracic tumors, chronic obstructive pulmonary disease, and chronic lung infections. The exact mechanism is uncertain, but it may be related to decreased arterial oxygen tension, or an unrecognized humoral substance that mediates connective tissue proliferation. The long bones of the forearms and lower extremities and the distal ends of the metacarpal and metatarsal bones are most frequently involved. Clubbing of the fingers and toes may occur, and arthritic symptoms may be manifested.



Regional Anatomic and Pathologic Roentgenography



CERVICAL SPINE



ROENTGENOGRAPHIC EXAMINATION


The standard roentgenographic views of the cervical spine include anteroposterior, lateral, and both posterior oblique views, as well as an open-mouth anteroposterior projection of the odontoid process and the first two cervical vertebral segments (Fig. 16-2). The majority of cervical spine studies are performed for the evaluation of trauma. In the more severely injured individual, the most important views are a cross-table horizontal beam lateral image and an anteroposterior supine film. By keeping patient movement to a minimum, potentially fatal spinal cord injury is prevented.



On the lateral exposure, C7 and occasionally C6 often are excluded, especially in heavy, short-necked individuals. In such instances, it becomes necessary to depress the shoulders by gentle but firm downward traction of the arms. If the cervicothoracic junction still has not been adequately visualized and severe injury to the neck has been excluded, a so-called swimmer’s view may be obtained. The patient lies in a prone-oblique position with the higher tube-side arm above the head and the lower table-side arm beside his or her body. The x-ray tube is angled 15 to 20 degrees toward the feet.


Other special projections can occasionally be of assistance. Flexion and extension lateral views often reveal minor degrees of subluxations resulting from damage to ligaments.


Dr. Don Weir of Saint Louis University developed the “pillar view” for better evaluation of the lateral articulating masses, the superior and inferior articulating facets, and their intervening joints. Moreover, this view brings into focus the anterior and posterior margins of the lamina (Fig. 16-3). The film is produced with the patient supine. Each side is done separately. The head is turned very slightly to one side, with the roentgenograph tube angled toward the feet 35 to 45 degrees and centered over the middle to lower vertebrae. The opposite side is then examined in a similar manner.



When available, CT with three-dimensional (3-D) reconstruction can eliminate plain film radiographs altogether for assessment of cervical spine trauma, and this can be performed quickly with minimal patient movement.



ROENTGENOGRAPHIC ANATOMY


A thorough understanding of the roentgenographic anatomy of the cervical spine is an absolute prerequisite to its proper evaluation. Each component of the individual vertebrae should be appraised separately on all views.



Odontoid View


Of the seven cervical vertebrae, the first two are anatomically distinct. The odontoid represents a superior extension of the body of C2 and is actually the vestigial body of C1. On the anteroposterior open-mouth film, the odontoid should be analyzed in terms of its position between the two lateral articulating masses of C1 (see Fig. 16-2, D). The spaces between the lateral edges of the odontoid and the medial borders of the C1 articulating masses should be equal. However, minor degrees of rotation can produce spurious inequality of these interval distances. How can this be determined? The alignment of the densities of the spinous processes of C1 and C2 can be seen. If the C2 spinous process is to one side or the other, then rotation is present.


Also on viewing the odontoid film, the transverse processes and lateral borders of the articulating masses of C1 and C2 should not be overlooked. The horizontal joints between the atlantoaxial articulating masses should be symmetric (see Fig. 16-2, D).


Confusing artifacts superimposed on the odontoid can be misleading and can result in misinterpretation of fractures of this structure. The inferior margin of the anterior or posterior arch of C1 can overlie the base of the odontoid and create a “Mach” effect, a radiolucent line produced by overlap of the edges of two bones. In a similar fashion, the space between the two incisor teeth may lay over the odontoid and yield an artifactual vertical cleft (Fig. 16-4).



It is not unusual for the odontoid process to be completely obscured by the base of the occipital bone if the head is held too far in extension. In such circumstances, have the view repeated with the patient’s head slightly more flexed.




Lateral View


Several important points must be remembered when viewing the lateral projection of the cervical spine (see Fig. 16-2, B). Alignments of the anterior and posterior borders of the vertebral bodies, alignment of the lateral articulating masses, and alignment of the spinolaminar line are studied. The latter is formed by the anterior margins of the spinous processes, which also describe the posterior surface of the spinal canal. The superior extension of this line is in direct alignment with the posterior margin of the foramen magnum.


The distance between a line drawn through the posterior borders of the vertebral bodies and the spinolaminar line provides the anteroposterior width of the spinal canal. This should measure no less than 13 mm from C3 through C7, being normally wider above C3. Any measurement less than this suggests the possibility of spinal stenosis.


The clivus at the base of the skull, which is a dense line continuous with the dorsum sella, is a helpful indicator for confirming normal craniovertebral alignment and should be included, at least in part, on all lateral studies of the cervical spine. A line drawn along its margin will pass through the posterior third of the odontoid.


The superior and inferior articulating facets ordinarily are well visualized on the lateral film. The posterior borders of the lateral articulating masses should form a straight line (see Fig. 16-2, B). If there is a slight offset, a facetal dislocation must be considered, although slight rotation can give a similar appearance. The view should be repeated if there is any confusion, and if the problem persists, CT scanning should be considered.


Measurement of the space between the anterior border of the odontoid and the posterior margin of the anterior arch of C1 is mandatory. This is an indicator of a possible transverse ligament tear and should measure no more than 5 mm in children and 3 mm in adults in neutral, flexion, and extension positions.


Finally, evaluation of the lateral cervical spine film is incomplete without an analysis of the prevertebral soft tissues. There are minor differences in the measurement from physician to physician and from patient to patient, but the width of the soft tissues at the level of the inferior margin of the C3 body should not exceed 5 to 7 mm. Any increase in this measurement indicates swelling from hemorrhage or infection.




TRAUMA


Recognition of an abnormal cervical spine should be a relatively simple task once normal roentgenographic anatomy has been mastered. After a traumatic lesion has been identified, the primary objective is the establishment of whether the condition is stable. The stability of a fracture is best determined by grouping the type of injury according to the mechanisms of trauma, which are outlined in Table 16-3. From this classification, a statement of the instability of the injury can be made (Table 16-4).


Table 16-3 Classification of Cervical Spine Injuries According to the Mechanisms of Injury*



































Flexion
Subluxation
Bilateral interfacetal dislocation
Simple wedge fracture
Flexion teardrop fractures
Clay-shoveler’s fracture
Flexion-rotation
Unilateral interfacetal dislocation
Vertical compression
Bursting fractures
Jefferson’s C1
Bursting fractures, other levels
Extension
Posterior neural arch fracture
Extension teardrop fracture
Hangman’s fracture

* From Harris JH Jr: Acute injuries of the spine, Semin Roentgenol 13:53–68, 1978. Used by permission.


Table 16-4 Classification of Cervical Spine Injuries Based on Stability*



























Stable
Subluxation
Simple wedge fracture
Unilateral interfacetal dislocation
Bursting fracture, except Jefferson’s fracture of C1
Clay-shoveler’s fracture
Unstable
Bilateral interfacetal dislocation
Flexion teardrop fracture
Jefferson’s bursting fracture of C1
Hangman’s fracture
Extension teardrop fracture, unstable in extension but stable in flexion

* From Harris JH Jr: Acute injuries of the spine, Semin Roentgenol 13:53–68, 1978. Used by permission.



Flexion Injuries


There are a variety of flexion injuries, which are described below.







Clay-Shoveler’s Fracture

This lesion is named for the injury acquired by people in occupations that require heavy lifting. This injury consists of a fracture through the spinous process of either C6 or C7 (Fig. 16-6). There is no significant ligamentous damage, and therefore a stable condition exists. Because C7 is sometimes difficult to project on the lateral film, the fracture can be missed. A clue might be apparent on the frontal film, where an extraspinous process fragment is sometimes evident as the result of inferior displacement. An unfused apophysis of a spinous process must not be misinterpreted as a fracture (Fig. 16-7).






Extension Injuries


Various extension injuries are described as follows.




Extension Teardrop Fracture

Similar to the flexion variety, an extension teardrop fracture demonstrates a triangular-shaped fragment at the anterior-inferior margin of the body, most often involving C2, although other levels are affected (Fig. 16-10). However, the injury is not quite as severe, because there is no posterior involvement. When the neck is held in flexion, there is stability of the spine because the posterior ligament complex is intact. However, instability occurs during extension because the minor fragment remains attached to the anterior longitudinal ligament but not to the parent body.





Vertical Compression Fractures


A considerable force directed through the vertical axis of the spine (such as a large object falling on top of the head or a diving injury) can produce the so-called bursting fractures of the cervical vertebrae. The least common type is the Jefferson fracture of C1. The anterior and posterior aspects of the ring are fractured on both sides, with bilateral lateral displacement of the fragments. This unstable injury can be apparent on the open-mouth anteroposterior film but more reliably is distinguished on the lateral roentgenogram where the fractures are seen to extend through the posterior arches.


Vertical compression or bursting fractures more frequently involve the middle and lower cervical vertebral segments. The longitudinally oriented pressures cause the intervertebral discs to impact against the end plates of the bodies. Ordinarily, there is no instability because the posterior elements remain intact. When viewed on the anteroposterior film, a vertical fracture line is identified within the involved body.


Although vertebra plana is not usually related to trauma, it might be mistaken for a compression fracture. This very rare condition, in most instances related to eosinophilic granuloma (histiocytosis X), has the appearance of a pancake with extreme, uniform flattening of the body but with preservation of the posterior elements. Some other possible causes for this unusual finding are metastasis, multiple myeloma, osteochondritis of the primary ossification center of the body (Calvé disease) and postradiation osteitis.



THORACIC AND LUMBAR SPINE




Roentgenographic Anatomy



Anteroposterior View


On the anteroposterior study, the 12 thoracic and 5 lumbar bodies show a slight increase in size from top to bottom. The height, width, and alignment of the bodies and their cortical margins, trabecular architecture, and density need to be scrutinized carefully.


Subsequently, the round-to-oval pedicles need to be evaluated separately. They overlie the superolateral corner of each body and, like them, become progressively larger inferiorly. The density and sclerotic cortical margins should be noted for any alterations, because they are involved in a number of pathologic processes.


The interpedicular distance, a line drawn between the inner boundaries of a vertebral body’s pedicles, is an important observation throughout the spine. It affords an indirect evaluation of the size of the neural canal.


The transverse processes in the thoracic spine become smaller from superior to inferior, are oriented posterolaterally, and are located behind the intervertebral foramina. The normal articulations of the ribs should not be overlooked. In the lumbar spine, the transverse processes are more laterally oriented and are much larger, the processes of the third vertebra usually being the largest.


On the anteroposterior projection, the spinous processes provide another guide for the evaluation of alignment. Rarely, they may be absent because of aplasia or malignant or infectious destruction.


Additionally, on the anteroposterior view, the paravertebral soft tissues should be studied. An increase in the width of the soft tissues alerts the clinician to a possible fracture, neoplasm, or infection in the spine, the result of hematoma, infiltrating tumor cells, or bacterial extension, respectively. The psoas margins in the paralumbar region are fairly sensitive indicators to similar changes when they become obliterated. This abnormal change can also reflect lymphadenopathy, hematuria, or urinary lesions such as a perirenal abscess. In fact, when viewing the lumbar spine, the clinician should always attempt to delineate the psoas and renal margins as well as search for urinary tract calculi as causes of back pain.




Oblique Views


Important anatomic features are introduced on the oblique views of the lumbar spine. These details have been covered more extensively in Chapter 8. On the left posterior oblique film (left side down against the film), the left half of the posterior neural arch elements, including the intervertebral foramina, are identified, whereas the right half of these components are viewed on the opposite projection. In the cervical spine, the reverse condition exists.



DEVELOPMENTAL VARIATIONS AND CONGENITAL ABNORMALITIES


Confusing anatomic variations are seen in the developing and mature spine. In infancy, the vertebral bodies are egg-shaped on lateral view. The upper and lower anterior corners are beveled until the apophyseal vertebral rings appear about each end plate. They fuse with the body by the fifteenth year, but occasionally they remain ununited and, except for the presence of a complete sclerotic border, often are confused with a corner fracture (Fig. 16-12). These are sometimes referred to as limbus vertebrae.



On the anteroposterior film, a vertical radiolucent cleft is seen superimposing on the vertebral bodies (Fig. 16-13). This represents the normal uncalcified portion of the posterior neural arch and spinous process and is not to be confused with spina bifida. At approximately 3 to 5 years of age, these will ossify and fuse. When they do fail to fuse completely, the cleft persists as a spina bifida occulta. This can occur anywhere in the spine, but is most common at L5. These are of no clinical importance.



True spina bifida is the result of a very wide defect in the posterior neural arch, usually involving multiple vertebrae and commonly found in the lumbar region. The widened spinal neural canal is evidenced by an increased interpedicular distance. These may be associated with a meningocele that produces a prominent posterior soft tissue density on the roentgenogram.


This wide gap of the dorsal arch and increased interpedicular width should also bring to mind the possibility of diastematomyelia, a condition in which the cord is divided by an intraspinal cartilaginous, fibrous, or bony spur. This has a predilection for the thoracolumbar junction. Syringomyelia can produce a similar appearance in the cervical spine where there is cystic dilation of the cord. The same type of appearance can also be seen with intraspinal tumors, such as lipomas or dermoids.


Vascular channels may give rise to confusing appearances. Blood vessels perforate the anterior cortical borders of each body and form a radiolucent line, termed the clefts of Hahn. A similar vascular defect that becomes more apparent in adulthood may exist along the posterior margin of the body.


Hypoplasia of the vertebrae, fusion or block vertebrae, and hemivertebrae constitute a few of the other possible spinal anomalies (Fig. 16-14).




TRAUMA


The focus of attention will now be shifted to some of the traumatic lesions involving the thoracolumbar spine. The majority of injuries disturb the muscular and ligamentous structures surrounding the spine. Just as in the cervical spine, the only visible roentgenographic findings may be scoliosis and/or straightening of the normal curvatures, which indicates muscle spasms. When a fracture is present, the usual appearance is a wedge-shaped compression deformity, the result of hyperflexion forces. Avulsion-type corner fractures of the anterosuperior body result from extension forces. They appear as a very sharp, nonsclerotic fragment as opposed to an unfused apophysis.


Quite frequently, the dilemma of determining the age of a fracture presents itself. In long-standing compression fractures, degenerative changes with hypertrophic spurs arise along the articular margins, and there may be an unpredictable degree of eburnation. Yet at times, these changes are absent, and the determination of age may be difficult, if not impossible. Radioisotopic bone scans that use 99mTc phosphate compounds then become a valuable aid. Within 2 to 5 days of the injury, a recent collapse shows an increased uptake of the isotope, whereas older lesions show no activity. However, the abnormal uptake may remain detectable for 18 to 24 months or longer, depending in part on the extent of the fracture and its location.


Wedge-shaped deformities of the vertebral bodies necessitate differentiation from other causative processes such as Scheuermann disease. This represents a form of osteochondritis or aseptic necrosis that involves the end-plate ring apophyses and is seen in adolescents. Described as juvenile kyphosis, it predominates in the thoracic region. Schmorl’s nodes commonly accompany this spinal affliction. These are rounded-to-oval protrusions of the anterior margins of the end plates and develop from focal intrabody herniation of the nucleus pulposus.


Biconcave deformities of the bodies, or so-called fish vertebrae, have a predisposition for the thoracic and lumbar location. They represent a chronic progressive form of compression characteristically seen in postmenopausal patients with osteoporosis. Vertebral body compression fractures with a history of minimal or no trauma should alert the physician to the possibility of a metastatic or primary malignant process.


Another important traumatic lesion, particularly of the lumbar spine, that can be easily overlooked is the transverse process fracture (Fig. 16-15). The importance of its recognition rests with the fact of frequently related renal injury. It is important not to mistakenly call the unfused apophysis of the transverse process a fracture.



A seldom-seen injury to the lumbar vertebrae is the Chance fracture (Fig. 16-16). An extreme flexion force, often related to seat belt injuries, causes a fracture through the spinous process, across the neural arch or lamina, and into the posterosuperior aspect of the vertebral body. An isolated fracture of the spinous process is uncommon in the thoracic and lumbar regions.



One more pitfall to watch for in the assessment of spinal trauma is the unfused ossification center of the articular facets, which can resemble a fracture (Fig. 16-17). In evaluating the posterior elements, it is important to keep in mind the entities of spondylolysis and spondylolisthesis (see Chapter 8).




TUMORS


Except for metastatic neoplasms to the spine, tumors—both benign and primary malignant lesions—are very infrequent. The vertebrae are the most commonly affected portion of the skeleton for metastasis and account for approximately 40% of all secondary tumors of bone. A few of the common and not-so-common tumors are discussed.











Chordoma and Sacrococcygeal Teratoma


There are two primary malignant tumors of the spine that are classified as developmental. A chordoma is an invasive lesion arising from remnants of the primitive notochord. It therefore can presumably occur anywhere along the vertebral column, although there are no reported cases of its occurrence in the thoracic region. The sacrum is the most popular site and accounts for approximately 50% of cases. An intracranial chordoma located along the clivus represents about 30% of cases, and the remaining 20% originate in the cervical and lumbar areas. Roentgenographically, the tumor presents as an expansile, lytic process with moderate soft tissue extension. As noted previously, it may cross the disc space cartilage, an uncommon occurrence of any tumor but typical of infections. In one third of the tumors, calcifications are observed. The second type of developmental primary malignant tumor is a sacrococcygeal teratoma. However, 60% of these lesions are benign but exhibit some degree of localized infiltration. They are found in infants, within the pelvis, around the parasacral region. Malformation of the spine can be an associated finding. The lesions appear roentgenographically as variable-sized soft tissue masses, often with calcifications or ossifications within them. The rectosigmoid colon is extrinsically displaced forward. Destructive changes are present to some extent within the sacrococcygeal bony structure. CT, MRI, or both modalities together can demonstrate these changes more accurately.



INFECTION


For obvious reasons, infections involving the spine have decreased in frequency over the years. Nevertheless, this must be considered in the differential diagnosis of a painful back and abnormal roentgenographic findings. Acute bacterial infections or pyogenic spondylitis can involve either the disc space, the vertebral body, or both. The former condition, termed pyogenic discitis, is more common in the younger population, apparently on the basis of a healthy vascularization of the cartilage and, therefore, easy access by blood-borne bacteria. This results in a closed-space infection that can secondarily extend into the bodies.


On the other hand, infection of the vertebral body, particularly its anterior two thirds, is more commonly identified in the adult. Originating in the substance of the body, the infection may then secondarily involve the interspace by extension.


An important principle in pathophysiology should be reemphasized at this point. Cartilage serves as no barrier to the extension of infection and thereby is vulnerable to destruction. Conversely, the disc cartilage is very resistant to malignant cellular infiltration, so tumors tend to remain confined to the body.


In both pyogenic discitis and vertebral osteomyelitis, the earliest roentgenographic findings may be joint space narrowing. Depending on the aggressiveness of the offending bacteria and the time of institution of therapy, the surrounding bone shows varying degrees of demineralization brought on by hyperemia. The end plates then demonstrate progressive loss of continuity with irregular destruction and focal areas of subchondral reactive sclerosis. Extension into the posterior third of the body, then into the dorsal appendages, as well as into the adjoining vertebrae, may occur. The body may eventually collapse. Some degree of surrounding soft tissue swelling is invariably present and detectable on roentgenograms and corroborated on MRI (Fig. 16-19).



Tuberculosis of the spine, or Pott’s disease, is an extreme rarity among today’s abnormal spine studies. The vertebral column remains the most common skeletal site for this chronic infection. The midthoracic and thoracolumbar junctions constitute the most prevalent sites of involvement.


Because of its insidious and chronic nature, the spinal lesions are usually advanced when first examined roentgenographically, although this is not always the situation. An occasionally prominent feature is a large paravertebral soft tissue mass that constitutes the abscess. In later phases, there may be extensive calcification within this mass (Fig. 16-20). The bony structures show a decrease in density, and there is narrowing of one or more of the disc spaces. The margins of the end plates manifest irregular destruction, and a mottled sclerotic and lytic appearance extends into the bodies, which display varying degrees of compression.




SPINAL ARTHRITIS


Arthroplasty of spondylosis of the spinal column most commonly is degenerative in nature with the formation of hypertrophic bony spurs. These osteophytes are formed by recurrent stimulation of wear and tear factors, and are predominantly located along the end-plate margins of the vertebral bodies. When they bridge the interspaces and fuse, such spurs are described as syndesmophytes, which can more often be identified in specific forms of arthritis, such as diffuse idiopathic skeletal hyperostosis (DISH; Fig. 16-21).



Ossification of the anterior longitudinal ligament of the spine is characteristic of ankylosing spondylitis (Marie–Strümpell disease). Psoriatic arthritis, Reiter disease, and other autoimmune diseases (including inflammatory bowel diseases) may lead to exuberant osteophyte formation.


Degenerative findings of the facet joints, particularly those of the lumbar spine, can result in various degrees of spinal stenosis. This is the result of bone spurs and soft tissue hypertrophy, primarily the ligamentum flavum. These produce narrowing of the central neural canal and can compromise the cord. Extension into the subarticular recesses and neuroforamina will encroach on the descending and exiting nerve roots, resulting in radiculopathy.


Degenerative disc disease is a commonly associated manifestation of arthritis. The aging process as well as trauma (either acute or related to chronic recurrent and repetitive injury) leads to eventual deterioration, dehydration, and protrusion or herniation of the nucleus pulposus through the annulus fibrosis. Broad-based posterior protrusion of disc material, along with degenerative hypertrophic spurs and thickened soft tissue elements, initiates the symptoms of spinal stenosis.



PAGET’S DISEASE


One of the distinctive roentgenographic characteristics of spinal Paget’s disease is that the disorder involves the entire vertebra—the body and all of the posterior elements, including the transverse and spinous processes (Fig. 16-22). Generally, there is an increase in density produced by a thickened trabeculae. A picture frame appearance can be imparted to the body, the result of a dense peripheral margin of thickened cortex. Furthermore, there is an actual increase in volume of the entire vertebra. This finding, along with total vertebral involvement, distinguishes Paget’s disease from an osteoblastic metastasis.




THE SHOULDER



ROENTGENOGRAPHIC EXAMINATION


In the majority of cases, a complete and optimal roentgenographic study of the shoulder girdle needs only include upright—standing or sitting—anteroposterior views with the humerus in internal and external rotation. These two projections usually permit adequate evaluation of the bony structures constituting the shoulder. In the uncooperative child or severely traumatized patient, these films may be obtained while the patient is in the supine position. On these roentgenograms, the complete clavicle should be visualized in addition to the entirety of the scapula and at least the proximal third of the humerus. Special attention should be given to the alignments of the glenohumeral, acromioclavicular, coracoclavicular, and sternoclavicular joints. The tuberosities of the humeral head and its articular surface should be specifically scrutinized. The acromium and coracoid processes, in addition to the borders and flat surfaces of the scapula, require attention.


The standard examination, of course, may require modification, because there are certain situations when special views must be obtained for better delineation of specific structures. In an acutely injured shoulder in which immobilization of the shoulder is required, the humerus ordinarily is held in internal rotation. To obtain roentgenograms of the humerus in external rotation without moving the arm, patients can be positioned by rotating them 40 degrees posteriorly with the affected side toward the film. Because of pain, this requires that patients be sitting or standing.


Upright exposures are also beneficial in demonstrating fat-fluid levels. This occurs when a fracture has extended into the joint through the articular cortex; this most often happens with fractures of the greater tuberosity. Such information is useful since articular cartilage damage is certain, and the patient should be informed that degenerative osteoarthritis in time is a possibility.


When there is suspicion of a fracture involving the shaft of the humerus below the neck, in addition to an anteroposterior view, a transthoracic lateral projection is necessary for evaluation of alignment (Fig. 16-23). The glenohumeral relationship can also be accessed with proper exposure, but because of superimposed ribs, fractures above the neck are difficult to see. Instead, a transscapular study is more helpful (Fig. 16-24). This view is obtained by having the patient face the film at an angle of 45 degrees with the affected side toward the film holder. The resultant picture forms a Y where the acromium, coracoid, and scapular body intersect. The humeral head will be superimposed on the Y. This is useful not only for fractures but also for posterior dislocations. This transscapular examination is always used when studying the scapula, in addition to the routine anteroposterior roentgenogram. CT or MRI imaging, particularly the latter, can provide additional valuable information especially regarding soft tissue involvement. The multiplanar capabilities of these imaging modalities augments visualization of gross pathologic findings.




Posterior shoulder dislocations are notorious for their ability to avoid detection on the standard anteroposterior views; they are frequently associated with seizure disorders. The tangential projection is an excellent means for detecting the abnormality. This is performed by angling the roentgen tube approximately 30 degrees so that the central ray passes tangentially across the glenoid articular surface. In this manner, the glenohumeral relationship is much better defined than on the conventional straight anteroposterior view.


The axillary film also provides another perspective of the shoulder anatomy (Fig. 16-25). The acromium, coracoid, glenohumeral joint, and humeral head are viewed in a different plane. By holding the film against the top of the shoulder, the picture is produced by abducting the arm and centering the roentgen tube through the axilla. The study requires a special “grid” cassette for the film. It is helpful in determining the presence of a humeral head displacement, but it is not recommended when a dislocation has just been reduced, because the required abduction may reluxate the joint.



The clavicle itself requires two projections in the anteroposterior plane to evaluate it properly. One film should be made perpendicular to the plane of the body, whereas the other exposure is made with a 15- to 20-degree cephalad angulation.


The acromioclavicular joints are best inspected with an anteroposterior film and tilting the roentgen tube 15 degrees toward the head. Comparative films are necessary to determine the presence of a separation, and this should be performed with and without weight bearing.


A more difficult area to examine roentgenographically is the sternoclavicular joint. Because of bony superimposition, CT may be required, but because this is not universally available, both oblique and lateral views may suffice. However, if these attempts are unsuccessful, the patient can be positioned prone. The roentgen tube is then centered through the sternoclavicular joints and angled toward the head at a 35-degree tilt.



ROENTGENOGRAPHIC ANATOMY AND DEVELOPMENTAL VARIATIONS


A considerable degree of confusion can be created by the ossification centers of the shoulder. The proximal humeral epiphysis does not become visible, as a rule, until the fourth to eighth month of life. There are two, occasionally three, separate centers. By the age of 20, the proximal epiphysis fuses to the shaft of the humerus. Before complete closure of the epiphyseal suture, the lucent line has a peculiar angulated appearance (Fig. 16-26). Overlap of the suture line occurs no matter what projection is used and consequently produces an image simulating a fracture.



A deceptive appearance of the proximal humeral shaft is the deltoid tuberosity, which, incidentally, receives the tendinous attachment of the deltoid muscle. The thickened cortex in this area may bring to mind the periosteal reaction of infection or tumor.


On a congenital basis, there may be a complete absence of the clavicle or at least partial underdevelopment of its lateral end. This represents hereditary cleidocranial dysplasia, a disease that also affects the skull, pelvis, hips, and other skeletal regions.


Normally, the outer end of the clavicle appears less dense than the middle and sternal aspects, the result of a lesser thickness of overlying soft tissue. Soft tissues are also responsible for a discrete line density paralleling the superior border of the clavicle that measures no more than 4 mm in width and is described as the “accompanying shadow.” This shadow may be thickened in cases of subtle fractures.


The rhomboid fossa is a familiar anatomic variation of the clavicle and is found along the inferior border at its medial aspect as a notch-like depression. This represents the location of the insertion of the costoclavicular (rhomboid) ligament, which secures the first rib to the clavicle. Its irregular appearance has been misinterpreted as a destructive process.



TRAUMA


Of all the joints in the body, the shoulder is the most frequent site of dislocations. More than 97% are anterior and can be described as subglenoid or subcoracoid, depending on the location of the humeral head. Invariably, this form of dislocation can be visualized by a single anteroposterior roentgenogram (Fig. 16-27). Whenever a dislocation occurs, it is not unusual to have an associated fracture; this should be searched for on the film. With an anterior dislocation, a fracture of the greater tuberosity may exist; the lesser tuberosity is vulnerable in posterior dislocations. The lower glenoid margin is also susceptible in either type of dislocation. An infraction of the articular cartilage without a visible fracture is also possible in dislocations and may require MRI to demonstrate.



Not infrequently with intraarticular extension of a fracture in the absence of true dislocation, an intact joint capsule may become progressively distended with blood, and if enough blood accumulates, there will be inferior displacement of the humeral head away from the glenoid. This condition is termed pseudosubluxation, or hanging shoulder.


With chronic recurring anterior dislocations, a defect becomes apparent along the superolateral aspect of the humeral head. This cortical infraction, present because of impaction against the anteroinferior rim of the glenoid, is commonly referred to as Hill–Sachs deformity. This abnormality is usually best demonstrated on an internally rotated anteroposterior view (Fig. 16-28).



The less frequent posterior dislocation is much more difficult to visualize roentgenographically. The problem arises because the humeral head on the standard anteroposterior projections shows no apparent separation from the glenoid fossa when in fact it is separated. The posterolateral orientation of the glenoid articular surface accounts for this to some extent. Ordinarily, in the normal shoulder the head of the humerus overlaps about three fourths of the glenoid fossa. When it becomes posteriorly dislocated because of lateral displacement of the head, this overlap is less, but the change may be very subtle. This perplexing situation can usually be solved by using the 30-degree tangential view, the axillary projection, or the transscapular film (Fig. 16-29). With recurrent posterior dislocations of the shoulder, a defect of the inferoposterior cartilagenous labrum may not be visible by stand-ard radiography. This is termed a Bankart lesion, which can be diagnosed by MRI or CT arthography.



A very rare form of dislocation of the shoulder joint is luxatio erecta, a condition where the humeral head is located under the glenoid rim and the humeral shaft is directed above the head in fixed abduction (Fig. 16-30). A lateral fall on an elevated arm produces such an abnormality. The acromium process of the scapula acts as a fulcrum pushing the head of the humerus down and out of the glenohumeral joint. The dynamics of the applied forces can result in a fracture of the acromium, the lower lip of the glenoid, or the greater tuberosity of the humerus. Often, there is an associated tear of the rotator cuff.



Fractures involving the proximal portion of the humerus are classified according to involvement of the head, either tuberosity, or the surgical or anatomic neck. Additionally, a fracture-displacement of the yet unfused epiphysis may occur.


For descriptive purposes, anatomists describe the surgical neck as that portion of the humerus just inferior to the tuberosities where there is a normal narrowing. The constriction or shallow groove at the articular margin of the head of the humerus is referred to as the anatomic neck.


Fractures of the proximal portion of the humerus must be evaluated by at least two views at right angles to one another. An anteroposterior view alone with a transthoracic lateral projection fulfills this criterion, but obliquely directed x-ray films may be necessary to best demonstrate displacement and/or angular deformity.


Transverse subcapital fractures of the surgical neck along with avulsions of the greater tuberosity are the most commonly encountered injuries to the shoulder. A fracture-displacement of the ununited epiphysis creates a more difficult diagnostic challenge. The normal epiphyseal line itself, as already mentioned, makes interpretation troublesome. The normal epiphysis has a uniform width and dense margins, whereas a fracture demonstrates varying thickness with a sharp, nonsclerotic edge. Often, there is impaction or distraction of the fragments causing some degree of overlapping, which makes the diagnosis somewhat simpler. Of course, if the presence of an abnormality is uncertain or indeterminate, an accurate comparison with the opposite uninjured shoulder should be performed.


The infraglenoid area of the scapula is the most common location of fractures of this bone. The normal lucent nutrient canal in this region with its dense margins should not offer much concern. Instead of a discrete fracture line, only a zone of increased density offers any clue to the injury. The clinician should also search for underlying rib fractures.


A complete fracture of the clavicle in most circumstances will exhibit overriding of the fragments when they involve its midportion. Because of the forces applied by the pectoralis minor muscle, as well as the weight of the arm, the lateral fragment is displaced inferiorly in most cases. An incomplete or nondisplaced fracture may be so subtle as to avoid detection initially, but the two standard views, including straight anteroposterior and cranially angulated projections, will in most instances reveal the fracture.



TUMOR


The proximal aspect of the humerus is a relatively common location for a benign solitary cyst, which may appear as either simple or multiloculated (Fig. 16-31). Such cysts are found within the metaphysis and exhibit destruction of the medullary spongiosa with more or less expansion of the bone. Thinning of the cortex can attain paper thickness, and pathologic fractures are a very common event, even in the absence of significant trauma. When initially discovered, the cysts extend to the epiphyseal line but do not involve the growth center itself. When followed serially until fusion of the epiphysis, the cyst appears to “migrate” toward the middle of the shaft as growth of the bone ends progresses.


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Jun 12, 2016 | Posted by in ORTHOPEDIC | Comments Off on Radiologic Aspects Of Orthopedic Diseases

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