5 1. Bony anatomy • Because there are seven cervical vertebrae and eight cervical nerve roots, roots exit above their respective vertebrae until C8 exits below the C7 vertebrae. After this, thoracic and lumbar nerve roots exit below their respective vertebrae. This is important to understand when evaluating potential root impingement. • Thirty-three vertebrae (seven cervical, 12 thoracic, five lumbar, five sacral, four fused coccygeal) comprise the osseous components of the spinal column (Fig. 5.1). 2. Alignment • Cervical lordosis • Thoracic kyphosis (normal 20–40 degrees; average 35 degrees) • Lumbar lordosis (normal 40–70 degrees; average 55–60 degrees) • Sacral kyphosis 3. Topographic anatomy (Table 5.1) • Topographic anatomy is important in planning your incision for surgical approaches. 4. Cervical spine (Fig. 5.2) • C1 (atlas) consists of anterior arch, posterior arch, two lateral masses; has no vertebral body or spinous process a. C1 articulates with occipital condyles of skull via two superior-oriented facets. b. Occiput–C1 (atlanto-occipital) articulation responsible for ~ 50% of the neck flexion/extension arc c. Structures at risk during surgery: internal carotid artery from penetration of anterior cortex of C1 lateral mass; vertebral artery from lateral dissection on the posterior arch • C2 (axis) consists of a vertebral body and the dens (odontoid process), which articulates with the anterior arch of C1 via a diarthrodial joint. a. Synchondrosis between dens and body fuses around age 7 b. Atlantoaxial C1-C2 articulation provides for ~ 50% of neck axial rotation Fig. 5.1 The bony spinal column (a) Anterior view, (b) posterior view, (c) left lateral view. Note that, phylogenetically, the transverse processes of the lumbar vertebrae are rudimentary ribs. They are often known as costal processes therefore. (From Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.) • Atlantoaxial joint complex a. Alar and transverse ligaments impart stability (Fig. 5.3). • Know the plane in which these ligaments resist translation. a. Transverse ligament attaches the posterior odontoid to each lateral mass of the atlas; major stabilizer of C1-C2; resists sagittal plan translation b. Alar ligaments run obliquely from tip of dens to occiput; resists lateral translation of odontoid (Fig. 5.4). c. Vertebral artery travels in transverse foramina of C6 through C2, then travels through the transverse process and along the top of arch of C1 d. Carotid tubercle is anterior tubercle of transverse process of C6
Spine
I. Anatomy of the Spine
C2-C3 | Mandible |
C3 | Hyoid cartilage |
C4-C5 | Thyroid cartilage |
C6 | Cricoid cartilage |
C7 | Vertebra prominens |
T3 | Scapular spine |
T7 | Tip of scapula |
L4-L5 | Iliac crest |
5. Thoracic spine
• T1 spinous process is long and prominent.
• Spinous processes are angled and overlap the subadjacent level.
• Costal facets allow articulation with ribs (present on thoracic vertebrae 1–12 and thoracic transverse processes of T1 through T9).
• Articulations with rib cage make thoracic spine a stable region of vertebral column.
6. Lumbar spine
• Large bodies are taller anteriorly than posteriorly, contributing to lumbar lordosis.
• Laminae increasingly overlap the disk space level, moving from caudal to cranial; relevant when performing laminotomy for herniated nucleus pulposus (HNP) in mid/upper lumbar region
• Sacralization of L5: transverse process of fifth vertebra fused to sacrum unilaterally or bilaterally
• Lumbarization of S1: first sacral segment with rudimentary disk leading to additional motion segment (i.e., six lumbar vertebra)
• Recognizing sacralization or lumbarization is important when localizing the operative level in lumbar surgery and when placing iliosacral screws.
• Large-diameter pedicles; however, L1 and L2 pedicles have smaller diameter than T11 and T12
a. Smallest pedicle isthmic width: L1
• Pars interarticularis: osseous segment between superior and inferior articular processes; defect results in spondylolysis
a. Posterior elements bear 20% of biomechanical load in upright position.
• Iliolumbar ligament
a. Stout ligament attaching transverse process of L5 to ilium
b. Provides stability to lumbopelvic articulation; may be disrupted or avulsed from L5 transverse process in unstable vertical shear pelvic injuries
• L5 nerve root is relatively fixed and is draped over the sacral ala; at risk from displaced sacral fractures and misplaced iliosacral screws (anterior)
7. Sacrum
• Structure formed by fusion of five embryological sacral vertebrae
• Four pairs of sacral foramina allow passage of ventral and dorsal branches of first four sacral nerve roots
• Sacral canal opens caudally to sacral hiatus; contains fifth sacral root
Fig. 5.2 (a) First cervical vertebra (atlas). (b) Second cervical vertebra (axis) (From Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.)
Fig. 5.3 The ligaments of the median atlantoaxial joint. Atlas and axis, superior view. (The fovea, while part of the median atlantoaxial joint, is hidden by the joint capsule.) (From Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.)
Fig. 5.4 Degenerative changes in the cervical spine (uncovertebral arthrosis). Coronal section through the cervical spine of a 35-year-old man, anterior view. Note the course of the vertebral arteries on both sides of the vertebral bodies. The development of the uncovertebral joints at approximately 10 years of age initiates a process of cleft formation in the intervertebral disks. This process spreads toward the center of the disk with aging, eventually resulting in the formation of complete transverse clefts that subdivide the intervertebral disks into two slabs of roughly equal thickness. The result is a progressive degenerative process marked by flattening of the disks and consequent instability of the motion segments (drawing based on specimens from the Anatomical Collection at Kiel University). (From Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.)
8. Spinal ligaments: contribute to spinal stability (Fig. 5.5)
• Anterior longitudinal ligament (ALL)
a. Thicker centrally than peripherally
b. Generally thicker than posterior longitudinal ligament
c. Strong and resists extension
• Posterior longitudinal ligament (PLL)
a. Thicker over vertebral body, thinner yet wider over disks
• Annular tears (and disk herniation) typically occur lateral to PLL expansion where it is weakest
b. Resists hyperflexion of vertebral column
• Ligamentum flavum (LF)
a. Strongest spinal ligament, elastic
b. Runs from anterior surface of superior lamina to cranial surface of inferior lamina
c. Functions to maintain extension of adjacent vertebrae
d. Hypertrophy of LF contributes to neural element compression in degenerative spinal disorders
• Interspinous ligaments (Fig. 5.6)
• Supraspinous ligament: above C7 is continuous with ligamentum nuchae; limits flexion of vertebral column
9. Intervertebral disk (IVD) complex
• IVD along with vertebrae above and below and along with associated facet joints at each level form the functional spinal unit (FSU)
• Annulus fibrosis: outer, obliquely oriented, composed of type I collagen; highest tensile modulus to resist torsional, axial, and tensile loads
• Nucleus pulposus: inner, type II collagen, predominantly water (decreases with aging, converted to fibrocartilage)
• Lumbar spine intradiscal pressure highest in the sitting/flexed position with weights in hands; lowest in supine position
10. Facet joints
• Orientation varies by spinal level and dictates plane of motion.
a. Cervical: superior articular facets of the subaxial cervical spine (C3-C7) are oriented in a posteromedial direction at C3 and posterolateral direction at C7; variable transition between C3 and C7
b. Thoracic: coronal plane orientation; resists translation and axial rotation but allows for sagittal plane motion
c. Lumbar: superior articular facets oriented in posteromedial direction. Orientation is more vertical in sagittal plane in upper lumbar spine and becomes more coronal as you move in a caudal direction; coronal orientation resists anterior translation, vertical orientation resists axial rotation (Fig. 5.7)
• Position of superior articular facet in relation to inferior articular process:
a. Cervical spine: anterior and inferior
b. Lumbar spine: anterior and lateral
• Superior margin of superior articular process often contributes to nerve root compression in lumbar foraminal stenosis
11. Spinal cord anatomy
• Structural anatomy
a. Spinal cord extends from brainstem to L1-L2, terminating as the conus medullaris.
Fig. 5.5 (a) The ligaments of the spinal column. The ligaments of the spinal column bind the vertebrae securely to one another and enable the spine to withstand high mechanical loads and shearing stresses. The ligaments are sub-divided into vertebral body ligaments and vertebral arch ligaments. (b) Schematic representation of the vertebral body and vertebral arch ligaments. Viewed obliquely from the left posterior view. a. Vertebral body ligaments. b–d Vertebral arch ligaments (From Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.)
Fig. 5.6 The ligaments of the cervical spine:nuchal ligament. Midsagittal section, left lateral view. The nuchal ligament is the broadened, sagittally oriented part of the supraspinous ligament that extends from the vertebra prominens (C1) to the external occipital protuberance (see A; see also p.98 for the ligaments of the atlantooccipital and atlantoaxial joints). (From Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.)
b. Distal to conus medullaris the dural sac contains the cauda equine (a bundle of lumbar and sacral spinal nerves originating in the conus medullaris).
c. Dominant blood supply: anterior spinal artery
d. Vascular watershed area of thoracic cord located at T4-T9
• Functional anatomy
a. Ascending (sensory) and descending (motor) tracts can be visualized in cross-section (Fig. 5.8)
Fig. 5.7 Lumbar facet orientation: superior articular facets oriented in posteromedial direction. Orientation is more vertical in sagittal plane in upper lumbar spine and becomes more coronal moving in the caudal direction.
◦ Dorsal columns: posterior, ascending fibers transmit proprioceptive, vibratory, and deep touch sensations
◦ Lateral spinothalamic: lateral, ascending fibers transmit pain and temperature sensations.
◦ Ventral spinothalamic: anterior, ascending fibers transmit light touch sensation.
◦ Lateral corticospinal: lateral, descending fibers transmit voluntary motor function.
♦ Upper extremities: deep/central
♦ Lower extremities: superficial/peripheral
♦ Injured in central cord syndrome
• Central cord syndrome affects the upper extremity more than the lower due to the central location of the upper extremity fibers.
a. Upper extremity motor deficits greater than lower extremity motor deficits due to deep/central location of upper extremity fibers of corticospinal tract
◦ Anterior corticospinal: anterior, descending, voluntary motor
b. Nerve roots (Fig. 5.9)
◦ Thirty-one paired spinal nerves: eight cervical, 12 thoracic, five lumbar, five sacral, one coccygeal
Fig. 5.8 Long tracts of the spinal cord. C, cervical; L, lumbar; and S, sacral; T, thoracic. (From Duus P. Topical Diagnosis in Neurology. New York: Thieme; 1998. Reprinted with permission.)
Fig. 5.9 Location and designation of spinal cord segments in relation to the spinal canal: right lateral view. The longitudinal growth of the spinal cord lags behind that of the spinal column, with the result that the cord extends only about to the level of the first lumbar vertebra (L1). Note that there are seven cervical vertebrae (C1–C7) but eight pairs of cervical nerves (C1–C8). The highest pair of cervical nerves exit the spinal canal superior to the first cervical vertebra. The remaining pairs of cervical nerves, like all the other spinal nerve pairs, exit inferior to the cervical vertebral body. The pair of coccygeal nerves (gray) has no clinical importance. (From Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.)
◦ In the cervical spine, the nerve root exits above its corresponding vertebral level (e.g., C5 root exits the C4–C5 foramen); in the thoracic and lumbar spine, the nerve root exits the foramen of its respective vertebral level (e.g., fourth lumbar root exits the L4–L5 foramen).
◦ Dorsal root/ganglia and ventral root converge to form the spinal nerve; once the nerve exits the foramen it gives off dorsal primary rami supplying muscles and skin of the neck and back, and a ventral ramus supplying the anterior trunk and all extremities.
◦ Sinuvertebral nerve: reenters the intervertebral foramen and innervates facet joints, annulus fibrosis, and IVD
♦ Mediates/transmits pain signal in degenerative disk disease
c. Autonomic nervous system
◦ Sympathetic ganglia: three cervical, 11 thoracic, four lumbar, four sacral
◦ In cervical spine, ganglia lie posterior to carotid sheath and anterior to longus capitis muscle
◦ Horner’s syndrome: disruption of inferior cervical ganglia (ptosis, miosis, anhidrosis)
◦ Seen with preganglionic lower trunk brachial plexus lesions
◦ Parasympathetic fibers from sacral levels for the pelvic splanchnic nerves combine with sympathetic fibers to form the hypogastric plexus; at risk with anterior lower lumbar dissection and can result in retrograde ejaculation
♦ Neurologic levels (Table 5.2) and physical exam (Fig. 5.10)
▪ Reflexes:
• Generally, hyperreflexia, clonus and positive Babinski sign, are indicative of cervical myelopathy
• Pathological reflexes:
Hoffman’s sign: elicited by quickly flicking the middle finger into flexion; a positive sign is noted when thumb and index fingers flex in response; may indicate myelopathy
Inverted radial reflex: noted when thumb and fingers flex during brachioradialis reflex testing; may also indicate myelopathy
▪ Special tests and provocative maneuvers:
• Lhermitte’s sign: shocklike sensation in trunk or extremities associated with axial load combined with flexion or extension of neck
• Spurling maneuver: progressive rotation, lateral bending and extension of neck to affected side exacerbates symptoms of radiculopathy
• Femoral nerve stretch test (L2-L4): flexing knee and hyperextending hip while patient is in a lateral decubitus position can reproduce symptoms of radiculopathy
• Straight-leg raise (L4-S1): can be performed supine or sitting, a positive test reproduces symptoms of radiculopathy
• Reproduction of pain with a contralateral straight leg raise enhances specificity.
Lasegue’s sign: pain aggravated by dorsiflexion of ankle
Kernig’s sign: pain aggravated by flexion of the neck
12. Surgical approaches
• Anterior cervical (Fig. 5.11)
a. Interval: between midline viscera (i.e., trachea and esophagus) and the carotid sheath
• Omohyoid muscle crosses surgical field in ventral approach
b. Complications
◦ Dysphagia and dysphonia common; usually resolve
♦ Equally likely after right/left sided approach
♦ May require hospital admission if swallowing dysfunction severe in early postoperative course or if swelling is concerning
♦ Work up for persistent problems: laryngoscopy/ear, nose, and throat (ENT) referral
♦ Unilateral vocal cord dysfunction is contraindication to contralateral approach
◦ Vocal cord paralysis and hoarse voice
♦ Due to recurrent laryngeal nerve injury
♦ Recurrent laryngeal nerve arises from vagus nerve at level of subclavian artery on right side (arises from aortic arch on left); injury results in unilateral vocal cord paralysis and hoarse voice
Fig. 5.10 The pattern of radicular (segmental) sensory innervation. The skin area supplied by a dorsal spinal nerve root is called a dermatome. Because the C1 segment consists entirely of motor fibers, it lacks a corresponding sensory field. Knowledge of radicular innervation is very important clinically. For example, when a herniated intervertebral disk is impinging on a sensory root, it will cause sensory losses in the affected dermatome. The area of sensory loss can then be used to locate the level of the lesion. Which intervertebral disk is affected? In a patient with shingles (herpes zoster inflammation of a spinal ganglion), the dermatome supplied by that ganglion will be affected (after Mumenthaler). (From Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.)
Fig. 5.11 Transverse section through the neck at the level of the C6 vertebra, superior view. (From Schuenke M, Schulte E. General Anatomy and the Musculoskeletal System: Thieme Atlas of Anatomy. New York: Thieme; 2005. Illustration by Karl Wesker.)
◦ Horner’s syndrome: due to injury to sympathetic ganglion; injury to inferior stellate ganglion results in ptosis and constriction of the pupil
◦ Intraoperative nerve injury
♦ C2–C3: hypoglossal nerve
▪ Leads to tongue deviation toward side of injury
▪ At risk with posterior C1-C2 transarticular screw placement
♦ C4–C5: superior laryngeal nerve; injury leads to fatigue of voice, hoarseness
◦ Airway compromise
◦ Acute dyspnea within the first 6–12 hours after surgery after cervical spine surgery may indicate an enlarging hematoma, and the incision should be emergently reopened.
♦ < 24 hours: hematoma; may warrant urgent decompression
♦ 24–72 hours: laryngopharyngeal edema; may require definitive airway control
♦ Late (> 72 hours): abscess, cerebrospinal fluid (CSF) accumulation, construct failure
♦ Airway complication prevention
▪ Consider maintaining intubation for 24–48 hrs postop for complex/prolonged procedures with extensive dissection, and for surgical time > 5 hours, with > 300 mL blood loss, focused above C3–C4
♦ Risk factors: exposure of more than three vertebral bodies, exposures involving the C2-C4 levels, blood loss > 300 mL, surgical time > 5 hours, and patients undergoing combined anterior/posterior procedures
◦ Vertebral artery injury: dissection lateral to the uncinate process can lead to injury to the vertebral artery as it ascends in the transverse foramen of the cervical vertebrae.
♦ Most asymptomatic due to collateral flow
♦ Injury to dominant artery may result in vertebral artery insufficiency (dizziness, dysarthria, dysphagia, diplopia, blurred vision, and tinnitus) or hindbrain infarct.
c. Revision surgery
◦ Revision anterior approach safest within 2 weeks of initial surgery before adhesion formation
◦ > 2 weeks postop, posterior approach may be advised
◦ Revision for pseudarthrosis
♦ Posterior fusion has higher fusion rate, lower reoperation rate, higher blood loss, longer hospitalization, increased complication rate compared with anterior revision
• Posterior cervical
a. Interval: midline paracervical muscles
b. Risks:
◦ Vertebral artery: vulnerable with lateral dissection at level of C1; exits transverse foramen, travels medially and superiorly, and enters atlanto-occipital membrane
◦ C5 palsy postoperatively: most common nerve palsy after posterior approach, motor dominant
• Transthoracic
a. Interval: through rib bed usually one to two levels above site of anterior column pathology
b. Leads to reduced pulmonary function postoperatively that often remains long-term
c. Risks:
◦ Intercostal neurovascular bundle
◦ Aorta, segmental arteries, artery of Adamkiewicz, thoracic duct (use right sided approach to avoid)
◦ Lung pleura
◦ Esophagus
• Posterior thoracolumbar
a. Interval: midline approach
b. Risk:
◦ Segmental vessels
• Anterior lumbar
a. Transperitoneal or retroperitoneal
b. Structures at risk:
◦ injury to hypogastric plexus can lead to retrograde ejaculation.
◦ Transperitoneal: bladder, bowel, great vessels (bifurcation at L4-L5 disk), median sacral artery, lumbar superior hypogastric plexus (retrograde ejaculation), sympathetic chain descends along anterolateral aspect of spine into the pelvis
◦ Retroperitoneal: great vessels, hypogastric plexus (retrograde ejaculation), ureters
13. Halo placement
• Appropriate pin placement: 1 cm above lateral third of orbit at or below equator of skull
• Adults/adolescents: usually four pins at 8 inch-pounds of torque
• Children: require more pins (8–10) at 2–4 inch-pounds of torque
• Adults get four pins at 8 inch-pounds, and children get the opposite, eight pins at 4 inch-pounds.
• Contraindications: skull fracture, skin defect over pin site
a. Sinus in too medial-frontal a position; supraorbital nerve
b. Temporalis fossa/muscle in too lateral a position
c. Too much traction: cranial nerve VI (abducens) palsy
II. Spinal Trauma
1. Spinal cord injury
• Background
a. Most common in young males
b. Most common causes: motor vehicle accidents, falls, gunshot wounds, and recreational/sports injuries
c. Cervical spine clearance: computed tomography (CT) or magnetic resonance imaging (MRI) required in obtunded patient
d. Spinal shock
◦ Characterized by flaccid areflexic paralysis and sensory loss
◦ Absent bulbocavernosus reflex
◦ Some neurologic recovery may occur when spinal shock resolves
◦ Typically resolves within 48 hours and is marked by return of bulbocavernosus reflex
◦ The level of injury cannot be determined until spinal shock has resolved.
◦ Following spinal shock, hyperreflexia, spasticity, and clonus develop.
e. Neurogenic shock
◦ Know the difference in clinical presentation between neurogenic and spinal shock.
◦ Systemic hypotension caused by interruption of sympathetic output to heart and peripheral vasculature; relative bradycardia (differentiates from hypovolemic shock)
◦ Treatment: vasopressor support
• Classification:
a. Complete/incomplete
◦ Complete injury: no preservation of sensorimotor function caudal to the injured spinal segment
◦ Incomplete injury: partial preservation of sensorimotor function caudal to the injured spinal segment
◦ Neurologic level: most caudal segment of spinal cord with intact sensory function and at least grade 
motor function
◦ Thorough neurologic examination establishes the level of spinal cord injury following the return of the bulbocavernosus reflex.
◦ Complete and incomplete injuries can be distinguished by the absence or presence of sacral sensation or distal sparing.
b. American Spinal Injury Association (ASIA) classification
◦ ASIA classification goes from worst (A) to best (E).
◦ ASIA A: complete loss of sensory and motor function below level of injury
◦ ASIA B: sensory function but no motor function below level of injury
◦ ASIA C: sensory function and partial preservation of motor function, but key muscle groups less than grade 
strength
◦ ASIA D: sensory function and useful motor (at least half the muscles have a grade of at least 
) below level of injury
♦ Function following spinal cord injury (according to level):
▪ C1, C2, C3: ventilator dependent with limited talking; electric wheelchair with head or chin control
▪ C4: possibly ventilator independent; electric wheelchair with head or chin control
▪ C5: ventilator independent likely; electric wheelchair with hand control; unable to live independently
▪ C6: manual wheelchair; able to live independently
▪ C7: improved use of a manual wheelchair; independent transfers
▪ Patient can independently transfer only if C7/triceps function is maintained.
• Medical management of spinal cord injury
a. Hemodynamic, respiratory, and cardiac support/monitoring; maintenance of mean arterial pressure (MAP) > 85–90 mm Hg
b. High-dose methylprednisolone: controversial due to question of efficacy and associated risks; use is based on hospital policy
◦ Proposed mechanism of action: reduced tumor necrosis factor-α (TNF-α) expression
◦ National Acute Spinal Cord Injury Study (NASCIS III) protocol:
♦ Indicated for patients with acute, nonpenetrating spinal cord injuries when treatment initiated within 8 hours of injury
♦ Less than 3 hours from injury: 30 mg/kg bolus, followed by 5.4 mg/kg/h for 24 hours
♦ 3 hours to less than 8 hours from injury: 30 mg/kg bolus, followed by 5.4 mg/kg/h for 48 hours
• Incomplete spinal cord injury syndromes
a. Brown-Séquard syndrome
◦ Penetrating trauma
◦ Ipsilateral loss of motor function and contralateral loss of pain and temperature sensation
◦ Best prognosis
b. Central cord syndrome
◦ Hyperextension injury (often in setting of preexisting cervical spondylosis/stenosis)
◦ Patients with cervical stenosis
◦ Bilateral upper > lower extremity weakness and sensory loss
◦ 35–45% chance of ambulation in ASIA C injuries in patients aged > 50 years
◦ Fair prognosis
◦ Most common incomplete spinal cord injury syndrome
c. Anterior cord syndrome
◦ Anterior cord has worst prognosis; Brown-Séquard has best prognosis
◦ Incomplete motor deficit below the level of injury
◦ Sensory deficit caused by injury to spinothalamic tract; posterior columns preserved (proprioception and vibration)
◦ Worst prognosis
• Surgical management
a. Decompression prior to 24 hours after spinal cord injury is associated with improved neurologic outcome, defined as an improvement of at least 2 grades on the ASIA C impairment scale at 6 months’ follow-up (Surgical Timing In Acute Spinal Cord Injury Study)
◦ Cervical spine fractures
• Occipital condyle fractures
a. Type I: impacted/comminuted condyle fracture resulting from axial load
◦ Mechanism: compression
◦ Alar ligaments and tectorial membrane intact
◦ Treatment: cervical collar
b. Type II: occipital condyle fracture with extension to or involvement of basilar skull
◦ Mechanism: compression
◦ Alar ligaments and tectorial membrane usually intact
◦ Treatment: cervical collar
c. Type III: avulsion fracture of occipital condyle
◦ Mechanism: distraction
◦ Results from avulsion of alar ligament
◦ Concern for underlying occipitocervical dissociation
◦ Treatment: immobilization in collar or halo versus surgery (occipitocervical fusion) depending on amount of displacement
• Occipitocervical dissociation
a. Background
◦ Commonly fatal
◦ Radiographically often challenging to diagnose (Fig. 5.12)
♦ Radiographic measurements:
▪ Powers ratio: distance from basion to posterior arch divided by distance from anterior arch to opisthion
• Value > 1.0 indicates atlantoaxial instability, possibly secondary to occipitocervical dissociation (anterior dislocation) (Fig. 5.13)
b. Harris method
◦ Basion–axial interval: distance from basion to line drawn tangential to posterior border of C2
♦ Less than 4 mm or greater than 12 mm is abnormal
◦ Basion–dens interval: distance from basion to tip of odontoid
♦ Greater than 12 mm is abnormal
c. Traynelis Classification
◦ Type I: anterior displacement of occiput on the atlas
◦ Type II: longitudinal distraction; any traction applied to type II injury can result in progression of existing deficit
◦ Type III: posterior subluxation or dislocation
d. Treatment
◦ Light traction may help reduce type I and III injures
◦ Immediate application of halo vest followed by occipital-cervical fusion with instrumentation for unstable injuries
• C1 (atlas) fractures
a. Isolated anterior or posterior arch fracture: nonsurgical treatment with immobilization
b. Lateral mass fracture: nonsurgical treatment with immobilization
