Occipital Condyle Fractures

Most injuries to the occipital condyles are caused by high-energy trauma to the head and neck. Bell reported the first case of occipital condylar fracture in 1817. The incidence of occipital condyle fractures is reported to range from 3% to 16%.^43,44

The clinical presentation of these injuries can range from minimal deficits to frank quadriparesis. Patients may complain of high cervical pain, torticollis, headaches, and impaired mobility. The most severe neurologic deficits are often seen with concurrent head injury. Up to 31% of these patients may exhibit acute lower cranial nerve deficits.

Although radiographs may show some abnormal soft tissue swelling in the presence of an occipital condyle fracture, these injuries are often extremely difficult to detect with conventional radiography (Fig. 76–2).⁴⁵

FIGURE 76–2 This patient was involved in a motor vehicle accident and complained of upper cervical spine pain. She was neurologically normal. A, This lateral radiograph shows increased soft tissue swelling in the upper cervical spine retropharyngeal area. The alignment of the spine appears normal. B, This coronal reconstructed computed tomography (CT) scan shows a fracture of the medial aspect of the left occipital condyle. It is minimally displaced. It is difficult to tell whether this is an impaction fracture of the occipital condyle or whether it is an avulsion due to tension on the alar ligament. C, This left sagittal reconstructed CT scan shows the minimally displaced occipital condyle fracture. The retropharyngeal soft tissue swelling can again be seen. D, This midsagittal T2-weighted magnetic resonance imaging (MRI) scan shows that there is adequate room for the spinal cord at this level. E, This MRI scan is a coronal image through the odontoid and through the alar ligaments bilaterally. The alar ligament on the left side (the same side as the occipital condyle fracture) is clearly intact. On the right side there is no cut that shows the alar ligament attaching to the odontoid. Presumably the alar ligament has been avulsed from the right side of the odontoid. This patient remained neurologically normal. She was immobilized in a rigid cervical collar for 8 weeks. The flexion and extension radiographs at that time showed that the spine was stable at the occipito-cervical junction. She was allowed to gradually resume her normal activities.

CT with reconstruction is the imaging modality of choice in the diagnosis and classification of these fractures. MRI can be used to assess for damage to the alar and tectorial membranes but is less useful than CT from a treatment perspective.

The most used classification system for occipital condyle injuries was described by Anderson and Montesano (Fig. 76–3).⁴⁶ The injuries are categorized into three types according to morphology and mechanism of injury. Type I injuries are impaction fractures of the condyle from axial loading. These fractures tend to be comminuted. The tectorial membrane and the alar ligaments are usually intact. Unilateral type I lesions are stable, but bilateral lesions may be unstable. Type II injuries are part of a more extensive basioccipital fracture that involves one or both occipital condyles. The common mechanism of injury is a direct blow to the skull. The tectorial and alar ligaments are intact, and the fracture is usually stable. Type III injuries are avulsion fractures near the alar ligament insertion that result in medial displacement of the condylar fracture fragment from the inferomedial aspect of the occipital condyle into the foramen magnum. The mechanism of injury is a forced rotation of the head combined with lateral bending. Type III fractures are potentially unstable injuries owing to avulsion of the alar ligaments.

FIGURE 76–3 These figures illustrate the best available classification for fractures involving the occipital condyles. A, This is an impacted occipital condyle fracture. In most cases this would be a stable injury and can be treated with a collar. B, This occipital condyle fracture is associated with a basilar skull fracture. In most cases this would be stable. C, This condyle fracture destabilizes the origin of the alar ligament and may be associated with significant occipitocervical instability.

(Reproduced with permission from Anderson PA, Montesano PX: Morphology and treatment of occipital condyle fractures. Spine 13:731-736, 1988.)

Type I and type II fractures can be treated with a rigid cervical orthosis. Type III injuries can be treated initially with an orthosis or halo vest. However, posterior occipitocervical fusion may be necessary for chronic pain, neurologic deficit, or instability.

In contrast to the majority of publications, Maserati and colleagues⁴⁷ reviewed 106 patients with occipital condyle fractures seen at a level one trauma center and found that only 3 required occipitocervical fusion. They suggested that each patient be evaluated looking for occipitocervical misalignment and that only those patients should be treated in a halo-vest or with a posterior fusion. The other 103 patients were successfully treated in a rigid cervical collar.⁴⁷

Atlanto-Occipital Injuries

The incidence of injuries to the atlanto-occipital joint is estimated to be between 5% and 8% of fatal traffic injuries.⁴⁸ These injuries account for 19% to 35% of all deaths from cervical spine trauma. More than 80% of cases of occiput-C1 dislocations were reported after 1975. Improvements in on-site resuscitation and emergency transportation have increased the number of patients who survive this catastrophic injury, which is typically the result of a motor vehicle accident. In a review of 146 traffic fatalities, Alker and colleagues⁴⁹ found a 5% incidence of occipitoatlantal dislocations. Children younger than 12 years of age are uniquely predisposed to this injury because their occipitoatlantal joints are flatter and because their head weight–to–body weight ratio is significantly greater than in adults.

Radiographically, significant retropharyngeal soft tissue swelling at C3 will be seen (Fig. 76–4). Multiple anatomic lines mark the normal relationship of occiput to C1. A line drawn down the cranial aspect of the clivus should be tangential to the dens (Wackenheim line). Distance greater than 10 mm between the basion and the dens is considered abnormal.⁵⁰ The sensitivity of this method is about 50%. An interval greater than 13 mm between the posterior mandible and the anterior atlas or 20 mm between the posterior mandible and the dens is abnormal (Fig. 76–5).⁵¹ The sensitivity of this method is 25%. Failure of a line drawn from the basion to the axis spinolaminar junction to intersect C2 or failure of a line from the opisthion to the posterior inferior corner of the body of the axis to intersect C1 is abnormal.⁵² The sensitivity of this method ranges from 20% to 75%. Powers’ ratio, the ratio of the distance from the basion to the posterior arch of the atlas divided by the distance from the opisthion to the anterior arch of the atlas, should be 1.0 or less in the absence of anterior occipitoatlantal dislocation (Fig. 76–6).⁵³ Another method to diagnose occipitoatlantal subluxation or dislocation on plain radiographs was described by Harris and colleagues.^54,55 They described a posterior axial line as the cranial extent of the posterior cortex of the axis body. If the distance between the basion and the posterior axial line (the basion-axial interval) is greater than 12 mm, or if the basion-dental interval is greater than 12 mm, then occipitocervical instability is present.^54,55 The sensitivity of this method varies from 76% to 100%.

FIGURE 76–4 This young man was involved in a motor vehicle accident with an unrecognized occipitocervical injury. A, Radiograph taken when the patient originally presented to the emergency department shows more than 2 cm of soft tissue swelling in front of C3. His injury was not recognized and he was discharged from the hospital. He was neurologically normal. B, Ten days later when the patient returned to the emergency department he had an obvious occipitocervical deformity. He was still neurologically normal. C, When the patient was placed in 5 lb of traction, it was apparent that he had separation between his occiput and C1 vertebra. D, Computed tomography (CT) shows that he has anterior displacement of his occipital condyle in relation to his C1 lateral mass, and he also has approximately 1 cm distraction of his occipitocervical joint. At the C2 level he also has a fracture extending into the lateral mass of C2. E, On the opposite side the same type of anterior subluxation of the occiput on C1 exists, as well as separation of the occipitocervical joint. F, Coronal reconstructed CT scan shows the pathologic distraction between the occiput and C1. You would expect only a 2-mm joint space at this level. G, Transverse CT scan shows that the patient has a vertebral artery course that is more medial than usual on each side and prohibited passage of C1-C2 transarticular screws. H, Midsagittal reconstructed CT scan shortly after surgery shows the large structural bone graft placed centrally between the occiput and C2. This was wired independently to the skull and spine and was necessary in addition to the plates and screws to ensure adequate healing and stability. I, Lateral radiograph of the spine was taken approximately 2 years after this patient’s injury. His spine has maintained normal alignment at the occipitocervical junction and stability has been restored.

(Reproduced with permission from Eismont FJ, Frazier DD: Cranial cervical trauma. In Levine AM, Eismont FJ, Garfin SR, Zigler JE [eds]: Spine Trauma. Philadelphia, WB Saunders, 1998, pp 205-206.)

FIGURE 76–5 This drawing shows the normal relationship of the posterior ramus of the mandible in relation to the anterior ring of C1 and the dens. Twenty-three normal patients were radiographed, and distance A averaged 2 mm with a range from −10 mm to +9 mm. The average for distance B was 10 mm with a range from 2 to 17 mm. Distances significantly greater than these averages denote anterior occipitocervical dislocation, and distances significantly smaller indicate likely posterior occipitocervical dislocation. All radiographs must be done with the patient’s mouth closed.

(Reproduced with permission from Dublin AB, Marks WM, Weinstock D, Newton TH: Traumatic dislocation of the atlanto-occipital articulation (AOA) with short-term survival—with a radiographic method of measuring the AOA. J Neurosurg 52:541-546, 1980.)

FIGURE 76–6 This drawing represents a midsagittal section through the craniocervical junction. B, basion; O, opisthion; A, anterior arch of the atlas; C, posterior arch of the atlas. The ratio of BC/OA should always equal 1 or less. If it is greater than 1, the patient most likely has an anterior occipitocervical subluxation or dislocation.

(Reproduced with permission from Powers B, Miller MD, Kramer RS, et al: Traumatic anterior atlanto-occipital dislocation. Neurosurgery 4:12-17, 1979.)

Because this is an unstable injury, flexion-extension views are not recommended. However, if they are available, there should be less than 1 mm of translation seen at the occipitoatlantal articulation. Instability is also present when there is distraction or marked asymmetry in the occipito-atlantal joints or when there are O-C1 level neurologic deficits present (Fig. 76−7). In children, more than 5-mm widening of the occipitoatlantal joints should raise the suspicion of this injury.

FIGURE 76–7 This elderly gentleman was involved in a motor vehicle accident and sustained pulmonary contusions and an upper cervical spine injury. He had cranial nerve 6 palsies with dysconjugate gaze, as well as cranial nerve 9 and 10 dysfunction with dysphagia and cranial nerve 12 dysfunction with lateral tongue deviation. He did not have any signs of myelopathy and his strength in all four extremities was normal. A, This lateral radiograph of the cervical spine shows grossly normal alignment and shows moderately severe retropharyngeal soft tissue swelling. B, A midline sagittal reconstructed computed tomography (CT) scan shows grossly normal alignment. C, This coronal reconstructed CT scan shows gross displacement of the occipital condyles from the C1 lateral masses. The spine is displaced approximately 1 cm to the right in relation to the skull. A fracture of the tip of the odontoid is also apparent. D, This right sagittal reconstructed CT scan shows marked widening of the joint space at the level of the occipital condyle and the lateral mass of the atlas. E, In the emergency department the patient was placed in a halo vest and his spine was reduced under fluoroscopic control. This coronal reconstructed CT scan shows good reduction of the occipito-cervical joint. The patient was intubated because of his pulmonary contusion. Approximately 12 hours after arrival in the emergency department, the patient was taken to surgery. He was turned to the prone position while in the halo vest, the posterior aspect of the halo vest was removed, and a posterior reduction and fusion was performed. F, This midsagittal reconstructed CT scan shows positioning of the structural autograft bone from occiput to C2 supplemented with allograft bone and cables. G, Screws were placed at the level of the skull and screws were placed at the level of the C2 pedicles and the C3 lateral masses. Bilateral plates were used. Supplemental cables were placed around the lamina of C1 and around the plates on each side. Following the surgery the patient was removed from his halo vest and mobilized in a rigid cervical collar. H, A follow-up radiograph at 6 months shows good alignment and a solid O-C3 fusion. He required supplemental stomach peg feeding for approximately 3 months before he was able to swallow without aspiration. His sixth cranial nerve palsy also resolved at approximately 6 months after the injury.

The most commonly employed classification system for occiput-C1 dislocations was described by Traynelis and colleagus⁵⁶ (Fig. 76–8), who categorized these injuries into three types. In type I injuries there is anterior displacement of the occiput on the atlas. Type II injuries are the result of longitudinal distraction. Any traction applied to a type II injury can result in progression of the existing neurologic deficit. Type III injuries involve a posterior subluxation or dislocation. Very light traction of about 5 lb applied to type I and type III injuries will help to reduce the dislocation and may improve the neurologic deficit. Radiographs should be taken immediately to ensure that there is no overdistraction.

FIGURE 76–8 These drawings represent the classification system of Traynelis and colleagues describing occipitocervical subluxation and dislocation.

(Redrawn from Traynelis VC, Marano GC, Dunker RO, et al: Traumatic atlanto-occipital dislocation. J Neurosurg 65:863-870, 1986.)

As noted earlier, the mortality from head-on-neck dislocation is extremely high. Only 20% of patients presenting to the trauma center with acute traumatic atlanto-occipital dislocation will have a normal neurologic examination.⁵⁷ The remainder will suffer deficits of the cranial nerves, brainstem, and upper cervical spinal cord. Vertebral artery injury may accompany the dislocation. The most common mechanism is from an extension-rotation force. Patients with vertebral artery insufficiency at this level may exhibit Wallenberg syndrome, consisting of ipsilateral defects of cranial nerves V, IX, X, and XI; ipsilateral Horner syndrome; dysphagia; and cerebellar dysfunction.

All occipitocervical dislocations should be treated initially by immediate application of a halo vest. Because the majority of these injuries are unstable, posterior occipitocervical fusion is the procedure of choice (Fig. 76–9).^32,58 This can be done using a variety of techniques including posterior wiring and structural grafting (Fig. 76–10), Ransford loop fixation with wiring (i.e., plate/rod and screw fixation with structural grafting) (Fig. 76–11). The first technique will require the use of postoperative halo immobilization, whereas the latter two techniques will usually only need collar immobilization as external support. Many instrumentation systems are currently available for occipitocervical fixation. Some use the thicker midline occipital bone and others rely on bilateral parasagittal occipital fixation.^59–61 Also described is the use of polyaxial screws into the occipital condyles as the sole point of fixation to the skull and then connecting to standard C-1 and C-2 screws bilaterally.^62,63

FIGURE 76–9 This man was injured when his car struck a tree. He had the immediate onset of pain in his upper cervical spine with radiation to the back of his head. A, Lateral radiograph shows normal alignment of the upper cervical spine and the occipitocervical junction. There is no abnormal soft tissue swelling. The basion appears to be directly over the tip of the odontoid and is less than 1 cm from the tip. Wackenheim line is not drawn here, but the bony line down the clivus and the posterior aspect of the basion appears to be tangential to the posterior aspect of the odontoid. B, Open-mouth view of the odontoid is abnormal. The patient’s right lateral mass of C1 appears smaller than the lateral mass of C1 on the left side. There is also some asymmetry, with the distance from the lateral mass of C1 to the odontoid being shorter on the right side than on the left side. C, Parasagittal computed tomography (CT) reconstruction shows that his occipital condyle on the right side is posterior to the lateral mass of C1. D, This image is slightly more medial than that in C and shows that the occipital condyle is impacted into the posterior aspect of the posterior lip of the right lateral mass of C1. E, This view is even more medial and again shows the occipital condyle to be posteriorly displaced and impacted into the posterior lip of the lateral mass of C1. F, Coronal reconstruction of the CT scan shows that the left-sided occipitoatlantal joint is normal. On the right side, the occipital condyle is posterior to the lateral mass of C1 and, hence, it is not seen on this view. G, This transverse axial image shows the abnormal appearance of the right-sided occipitoatlantal joint. H, The patient was initially placed in skull tong traction, but the occipitoatlantal dislocation could not be reduced. The patient was therefore taken to surgery. At the time of surgery with a combination of skull tong traction and manual manipulation with a cable passed under the posterior arch of C1, the occiput-C1 dislocation was reduced with an audible “clunk.” Fusion was performed using titanium cables to fasten autograft bone to the base of the skull posteriorly and to the posterior arch of C1. This postoperative coronal CT reconstruction shows complete reduction of the occipitoatlantal joints bilaterally. I, Lateral radiograph shows the bone graft and cables in place. Because rigid internal fixation was not used, the patient was immobilized in a halo vest postoperatively. J, Midsagittal reconstructed CT scan shows the bone graft healing at 3 months from the time of surgery.

FIGURE 76–10 A and B, These drawings represent the classic wiring technique for occipitocervical fusion. The titanium cables fastening the bone graft to the skull are passed through two bur holes just posterior to the foramen magnum. The cables are also passed bilaterally under the posterior arch of C1 and under the lamina of C2. Drill holes are made in the iliac crest bone graft to allow passage of the wires as shown. The cables under C2 are passed all the way around the graft. It is imperative that the graft be a thick structural iliac bone graft. If the bone graft is not solid enough, a combination of cortical structural allograft bone graft superficially and the patient’s autogenous iliac bone graft beneath this would be used to provide a combination of structural stability and autogenous factors to promote bone healing. If rigid instrumentation (plates or rods combined with screws) is not used, then the patient would be placed in a halo vest until the construct was completely healed. This would usually require a period of 3 months.

(Reproduced with permission from Eismont FJ, Frazier DD: Cranial cervical trauma. In Levine AM, Eismont FJ, Garfin SR, Zigler JE [eds]: Spine Trauma. Philadelphia, WB Saunders, 1998, p 203.)

FIGURE 76–11 A and B, These drawings represent anteroposterior and lateral views of the occipital cervical plating technique using C1-C2 transarticular screws and titanium reconstruction plates with bicortical skull screws. Because the transarticular C1-C2 screw is the most critical in terms of its positioning, the C1-C2 transarticular screw is always the first screw to be placed in this construct. The path would initially be drilled and tapped. A plate would then be bent to accommodate the local anatomy. The plate must fit flush against the skull, fit against the posterior arch of C1, and fit the contour of the posterior arch of C2. The C1-C2 transarticular screw is then placed through the plate and tightened to within two turns of its final position. The plate is then held against the skull, and two or three screws are then placed into the skull. The screws in the skull are always bicortical. The thickness in this area of the bone ranges from 4 to 6 mm. A cable is also usually passed under the posterior arch of C1 and passed around the plate and then tightened. These cables contribute significantly to the rigidity of the construct. After one side is secured, the second side is similarly instrumented. The C1-C2 screws are placed under lateral fluoroscopic guidance. The pedicle of C2 is dissected so that it can be visualized directly during screw insertion. The starting point for the C1-C2 screw is usually 3 to 4 mm cephalad to the C2-C3 facet joint. The distal tip of the screw should be just to the anterior cortex of C1. It can also protrude slightly through the anterior cortex, but it should be kept in mind that the internal carotid artery lies within a few millimeters of the usual anterior exit point for these screws.

(Reproduced with permission from Eismont FJ, Frazier DD: Cranial cervical trauma. In Levine AM, Eismont FJ, Garfin SR, Zigler JE [eds]: Spine Trauma. Philadelphia, WB Saunders, 1998, p 204.)

Fractures of the Atlas

Fractures of the atlas were first described by Jefferson in 1921. They usually occur in the anterior and posterior arches, which are the weakest points on the C1 ring. These injuries comprise 2% to 13% of all cervical spine fractures and approximately 25% of all injuries to the atlantoaxial complex.²² They are often seen in the younger age groups (mean age, 30 years) and are most commonly the result of vehicular accidents or a fall onto the top of the head.

These fractures are caused by axial loading. Because of this mechanism, these fractures commonly accompany head injuries in the polytrauma patient. In addition, there is an extremely high association (up to 50%) of atlas fractures with other cervical spine fractures. These include dens fractures, hangman’s fractures, teardrop fractures of C2, cervical burst fractures, and lateral mass fractures.²²

Patients will often complain of severe suboccipital discomfort and a sense of instability. Neurologic injury is uncommon in the case of isolated fractures of the atlas, but, when it occurs, the greater occipital nerve is most frequently injured, followed by the lower cranial nerves.⁶⁴

Retropharyngeal soft tissue swelling greater than 5 mm at C3 in combination with a fracture of the posterior arch of C1 is highly suggestive of a bursting-type injury. A combined lateral mass displacement on the open-mouth anteroposterior view exceeding 6.9 mm is indicative of transverse ligament insufficiency (Fig. 76–12),⁶⁵ but this measurement may not be sensitive enough to detect all unstable injuries. MRI can be used to help assess the continuity of the transverse ligament in those cases in which the ligament status is unclear.⁶⁶

FIGURE 76–12

This transverse CT scan at the C1 level shows a Jefferson fracture with significant spreading of the lateral masses of C1. This has resulted in the avulsion of the origin of the transverse ligament from the right lateral mass of C1 (arrow). The usual treatment for this would be a halo vest and mobilization for 3 months followed by flexion and extension radiographs to assess C1-C2 stability.

Fine-cut CT in the plane of the axis will clearly delineate the fracture pattern. Common fracture patterns include isolated posterior arch fractures, lateral mass fractures, and burst fractures with combined anterior and posterior arch fractures. Isolated posterior arch fractures (Fig. 76–13) most commonly occur at the vertebral artery groove at the junction of the lateral mass and the posterior arch. These are stable fractures that can be treated in a cervical collar for comfort. Lateral mass fractures can be either displaced or nondisplaced. Nondisplaced injuries can be treated with a cervical collar. Fractures that are displaced more than 5 mm can be treated with immediate halo vest application. Burst fractures of the C1 ring are often referred to as Jefferson fractures, and these injuries have one or two fractures in the posterior arch and one or two fractures in the anterior arch. Minimally displaced fractures (<7 mm) can be treated in a cervical collar.⁶⁷ Treatment of fractures with a combined diastasis of more than 6.9 mm consists of immobilization in a halo vest for 3 months (Fig. 76–14). After the halo vest is removed, flexion and extension radiographs are taken to test for C1-C2 instability, which, if significant, can be treated by C1-C2 posterior fusion.

FIGURE 76–13 This transverse CT scan at C1 shows minimally displaced fractures of the posterior arch of C1. This always occurs at the site of the vertebral artery groove. Provided no other fractures are associated with this, the patient can be immobilized in a cervical collar for a short period of time and for comfort only. By itself, this is a stable injury.

FIGURE 76–14 This patient sustained a moderately displaced Jefferson fracture in an accident. He was treated in a halo vest with no initial reduction. A, Open-mouth view of the C1-C2 joints shows a 2-mm overhang on the right and an 8-mm overhang on the left. B, Computed tomography (CT) scan at C1 shows the 8-mm lateral displacement of the left C1 lateral mass. C, This final CT scan shows that the lateral mass displacement is unchanged but there is now copious callus anteriorly between the anterior C1 arch, the C1 lateral mass, and the odontoid. D and E, Flexion and extension radiographs 1 year after the injury show no evidence of instability at C1-C2 or at the occipitocervical joints. He has had no pain since removal of the halo vest and is gradually resuming his preinjury activities with no restrictions.

Treatment of Jefferson fractures with greater than 6.9 mm of separation is controversial. Levine and Edwards advocate initial reduction of the fracture with skeletal traction for up to 6 to 8 weeks, followed by another 6 weeks of halo vest treatment.⁶⁸ Other series have found that immediate treatment with a halo vest can result in an acceptable outcome and avoids the morbidity associated with prolonged bed rest.^69,70 Traction reduction followed by early C1-C2 fusion using C1-C2 transarticular screws has also been described,⁷¹ but intraoperative difficulty may be found owing to gross instability of the C1 lateral masses and the loose C1 posterior arch.

Most surgeons would agree that operative treatment is indicated if more than 5 mm of C1-C2 instability exists on flexion and extension radiographs once the halo is removed. If the posterior arch of C1 is healed, a posterior C1-C2 fusion is indicated. In the case of nonunion of the posterior arch of C1 or significant injury to the occipital condyles, occiput to C2 fusion can be performed. Another indication for surgery is neck and/or occipital nerve pain in a patient with a nonunion of the atlas ring fractures. The recommended treatment would then be a posterior occiput-C2 fusion.⁷²

Atlantoaxial Subluxation and Dislocation

Conservative care of atlantoaxial rotatory subluxation in children, also known as Grisel syndrome, is most effective when treatment is instituted early. Most children who have had symptoms for less than 1 week will improve with a soft cervical collar and close observation. When symptoms have been present for 2 to 4 weeks, hospital admission and head-halter traction is usually successful in achieving reduction. For patients who present 1 month after the subluxation occurs, skull traction can be instituted and continued for up to 3 weeks. Initial traction should be 7 lb and gradually increased to 15 lb. If traction fails to reduce the deformity, open reduction and C1-C2 fusion are recommended.⁷³

Traumatic rotatory subluxation or dislocation in adults is most commonly caused by vehicular trauma. Like children, adults will present with a “cock robin” appearance with the head tilted toward and rotated away from the side of the dislocation.

Radiographs will show asymmetry of the lateral masses on the open-mouth view. A “wink sign” may be appreciated; it is caused by overriding of the C1-C2 joint on one side with a normally aligned joint on the contralateral side. Dynamic CT is the best means of demonstrating the condition. Cervical spine CT scans are done in a neutral position and then repeated with the head maximally rotated to one side and then the other side.

Fielding and Hawkins⁷⁴ presented the most commonly used classification scheme for these injuries (Fig. 76–15). Type I dislocations are pure rotational injuries. Type II injuries have both rotatory malalignment with anterior displacement of the atlas less than 3 to 5 mm, suggesting only a mild deficiency of the transverse ligament. Type III injuries combine rotatory subluxation with greater than 5 mm of displacement, suggesting complete deficiency of the transverse ligament. Type IV injuries have both rotational malalignment and posterior displacement.

FIGURE 76–15 These drawings show the four types of C1-2 rotatory fixation. A, Type I—rotatory fixation with no anterior displacement and the odontoid acting as the pivot. B, Type II—rotatory fixation with anterior displacement of 3 to 5 mm, with one lateral articular process acting as the pivot. C, Type III—rotatory fixation with anterior displacement of more than 5 mm. D, Type IV—rotatory fixation with posterior displacement.

(Reproduced with permission from Fielding JW, Hawkins RJ: Atlanto-axial rotatory fixation. J Bone Joint Surg Am 59:37-44, 1977.)

In adults, reduction of the rotational deformity can usually be achieved by skull tong traction. Topical anesthetic in the posterior pharynx may be helpful. The reduction can be palpated through the mouth. If it was difficult to obtain the reduction, then halo vest immobilization may be necessary. For most cases a rigid cervical collar is adequate.

If closed reduction fails, open reduction is performed and a posterior C1-C2 fusion is used to stabilize the reduction. Many methods to achieve fusion of the C1-C2 complex have been described including the Gallie technique, the Brooks technique, C1-C2 transarticular screws supplemented with a posterior fusion, and C1 lateral mass and C2 pedicle (or interlaminar) screw construct. The use of transarticular screws and screw-rod constructs provides sufficient fixation to obviate the need for postoperative halo vest immobilization. The other methods of stabilizing C1-C2 may be rigid enough to permit mobilization in a rigid collar or may require use of a halo vest to supplement the fixation, especially if it is difficult to achieve the reduction or if the bone quality is poor.

Rupture of the Transverse Ligament

The transverse ligament is the major ligamentous stabilizing structure for the atlantoaxial articulation. It is composed primarily of collagen fibers, which render it stiff and inelastic.⁷⁵ When torn or disrupted, it is incapable of repair and its original strength and function cannot be restored.

Insufficiency of the transverse ligament and subsequent C1-C2 instability is suspected if the atlantodens interval is greater than 3.5 mm in adults and greater than 5 mm in children on lateral radiographs and in atlas fractures when the combined overhang of the C1 lateral masses on C2 is greater than 6.9 mm on an anteroposterior open-mouth view of the upper cervical spine.^65,66 Plain radiographs, however, are often inadequate to assess suspected transverse ligament injuries; and a combination of MRI, CT, and dynamic radiographs is often necessary to fully assess the type and extent of injury.⁶⁶

Dickman and colleagues⁶⁶ classified transverse ligament injuries into two types. Type I injuries encompass intrasubstance ruptures. Type Ia injuries occur in the midportion of the ligament. Type Ib injuries occur at the periosteal insertion of the ligament onto the atlas. Type II injuries occur when there is an avulsion of the tubercular insertion of the transverse ligament from the C1 lateral mass. Type IIa injuries occur if the lateral mass is comminuted, and type IIb injuries occur if the lateral mass is intact.

Type I injuries should be treated surgically with C1-C2 fusion. The most common way to achieve this is posteriorly. Wiring techniques such as Brooks and Gallie fusions are effective more than 90% of the time⁷⁶ but are the least biomechanically stable,⁷⁷ and a rigid cervical collar is usually used for 3 months postoperatively. Transarticular screw fixation (Fig. 76–16) provides sufficient additional stability to allow the immobilization time to be reduced to 6 weeks in a rigid collar or even to allow the patient to be immobilized in a soft cervical collar. There is, however, risk to the vertebral artery when instrumentation is done across the pars interarticularis of C2. C1 lateral mass screw and C2 pedicle screw constructs provide comparable biomechanical rigidity to transarticular screws with less risk to the vertebral artery but with more risk to the internal carotid artery. If necessary, sacrificing the C2 nerve root provides direct visualization of the C1 lateral mass and the C1-C2 joint. The structures can then be instrumented, reduced, and fused under direct visualization. The combination of C1 lateral mass screws connected to C2 translaminar screws is another alternative fixation option that provides the same degree of stability of the C1-C2 complex. C1-C2 fusion can also be achieved by an anterior approach with anteriorly placed C1-C2 screws.⁷⁸ Proponents of this technique note that there is less soft tissue dissection involved as compared with posterior approaches.⁷⁹ We, however, recommend the posterior approach in order to provide better supplemental bone grafting and to minimize postoperative swallowing and airway problems.

FIGURE 76–16 These lateral and anteroposterior views show the technique described by Grob and colleagues. They advise having the start point 3 to 4 mm cephalad to the C2-C3 facet joint and have it as medial as possible without penetrating the medial wall of the C2 pedicle. They emphasize seeing the medial and superior aspects of the C2 pedicle and also the C1-C2 joint. The anterior aspect of the screw should be either to the anterior cortex of C1 or just through it. As mentioned in the legend to Figure 76–11, the internal carotid artery lies just anterior to the usual exit point for the C1-C2 transarticular screw and, hence, it is extremely important that the screw tip either not protrude anterior at all or only a minimal distance. The illustration also demonstrates placement of an autogenous bone graft between the arches of C1 and C2 and adequately tightening the wires or cables, which, together with the C1-C2 transarticular screws, makes this an extremely strong construct. Packing bone graft within the C1-C2 joint may be done, but it adds considerably greater risk to the procedure and does not seem to be necessary under usual circumstances. It is necessary to perform fine-cut CT sagittal reconstruction views of C1 and C2 from side to side to be certain that there is adequate room for placement of a C1-C2 transarticular screw without compromising the vertebral artery. In approximately 15% of cases local anatomy of the vertebral artery precludes placement of two screws. Placement of one screw in combination with the posterior bone graft seems to be adequate.

(Reprinted with permission from Grob D, Jeanneret B, Aebi M, Markwalder T: Atlanto-axial fusion with transarticular screw fixation. J Bone Joint Surg Br 73:972-981, 1991.)

Type II fractures can be treated with external immobilization for 3 months. Up to 74% of these type II injuries will heal with nonoperative care.⁶⁶

Fractures of the Odontoid

Fractures of the dens constitute 7% to 13% of all cervical spine injuries.⁸⁰ They are frequently missed because of the paucity of clinical symptoms other than for neck pain. In addition, if the patient suffers from head trauma and is intoxicated or obtunded, the injury can be easily missed. Both flexion and extension mechanisms can cause fractures of the dens. Hyperflexion results in anterior displacement of the dens fracture, and hyperextension results in posterior displacement of the dens fracture.

The fracture can usually be seen on open-mouth and lateral radiographs of the cervical spine, although nondisplaced fractures can easily be missed. Classification of these fractures is based on their location in the odontoid. The most commonly used classification scheme was described by Anderson and D’Alonzo (Fig. 76–17).⁸¹ Type I fractures consist of avulsion injuries at the tip of the dens. Type II fractures occur through the base of the dens at the junction of the dens and the central body of the axis. Type III fractures extend into the body of the axis.

FIGURE 76–17 These drawings represent the three types of odontoid fractures. Type I is an oblique fracture at the tip of the odontoid process. It is usually an avulsion of bone at the insertion of the alar ligament. This is normally taught to be a benign injury, but it can be seen in significant occipitocervical injuries. Type II is a fracture at the neck or base of the odontoid but before it goes down into the body of the axis. This area has a poor blood supply and the smallest cross-sectional area and hence has a lower potential for healing. A type III fracture extends down into the body of the axis. It therefore has a larger surface area compared with a type II fracture, and there is also a much greater ratio of cancellous bone to corticol bone. Type III fractures have a better healing potential than type II fractures.

(Reproduced with permission from Anderson LD, D’Alonzo RT: Fractures of the odontoid process of the axis. J Bone Joint Surg Am 56:1663-1674, 1974.)

Type I injuries can be treated nonoperatively with a rigid cervical collar, but the possibility of occipital cervical instability must first be ruled out because the bone avulsion always means that at least one alar ligament is incompetent. After 3 months of immobilization, flexion and extension radiographs are taken to assess for healing and residual ligamentous instability.

Type II odontoid fracture is the most problematic type of odontoid fracture. In a prospective study of 144 odontoid fractures reported by the Cervical Spine Research Society,⁸² there were 96 type II and 48 type III fractures. The incidence of spinal cord level neurologic deficits was 14 of 96 (14%) of type II fractures and 4 of 48 (8%) of type III fractures. Two of the 14 patients with type II fractures and cord deficits presented with upper extremity monoplegia, which probably represents the cruciate paralysis described earlier in this chapter.

In this same prospective study, of the 38 patients with type II fractures treated primarily in a halo vest, only 66% had a successful result, with 7 patients (18%) having nonunions, 3 having malunions, 2 having fracture displacement, and 1 dying before union. Of the 16 patients with type III odontoid fractures treated primarily in a halo vest, 13 (81%) had a successful outcome, with one nonunion, one fracture displacement, and one death, which occurred 1 day after injury due to cardiac arrest. Of the 30 patients (including both type II and III fractures) treated primarily with a posterior C1-C2 fusion, 96% had a successful outcome with only one nonunion.

The overall nonunion rate for type II odontoid fractures is reported to be about 32%. There is an increased nonunion rate associated with fractures with greater than 5 mm of displacement, angulation greater than 10 degrees, age older than 40 years, and posterior displacement.⁸³ Hadley showed a 78% nonunion rate for type II fractures displaced more than 6 mm in comparison with a 10% nonunion rate when the displacement was less than 6 mm.⁸⁴

Treatment options need to be individualized for each patient. Halo vest treatment may be a good option for a patient with an undisplaced type II odontoid fracture or an undisplaced/minimally displaced type III odontoid fracture in a patient with few or no risk factors for nonunion. The patient needs to understand, however, that even with 3 months of halo vest treatment there is still a risk of at least 10% that surgery will be necessary to treat the fracture. As the amount of displacement and angulation increases and as the number of other risk factors such as more advanced age and smoking increases, then the chance of failing to heal appropriately in a halo vest becomes significantly large.

As the risk factors for nonunion increase, surgical treatment with a C1-C2 fusion or anterior odontoid screw fixation becomes a better option. If primary C1-C2 fusion is selected, the patient should understand that he or she will lose 50% of neck rotation. Many options exist for fixation and fusion of C1-C2. C1-C2 transarticular screws (Fig. 76–18),⁸⁵ C1 lateral mass/C2 pedicle screw constructs (Fig. 76–19), and C1 lateral mass/C2 translaminar screw constructs (Fig. 76–20) offer a biomechanical advantage over traditional wiring techniques and should minimize the chance of losing the fracture reduction and maximize the chance of having a solid fusion.⁸⁶ A fusion rate and fracture union rate of 98% should be expected. If wiring techniques are used, a fusion rate of 94% to 96% can be expected, but there will be a higher chance of losing reduction. Gallie-type constructs are biomechanically advantageous for anteriorly displaced fractures, whereas Brooks constructs are advantageous for posteriorly displaced fractures.

FIGURE 76–18 This patient sustained a type II odontoid fracture in a motor vehicle collision. She was neurologically normal but complained of neck pain. A, Initial lateral radiograph shows a minimally displaced type II odontoid fracture. There is a slight gap anteriorly at the fracture site. The patient was kept immobilized in a rigid collar and was sent for a computed tomography (CT) evaluation. B, Midsagittal reconstruction of the CT scan shows that the fracture has displaced 12 mm anteriorly. This fracture was obviously more unstable than it initially appeared. C, Parasagittal CT reconstruction is necessary to be certain that there is an adequate path for the C1-C2 transarticular screw. In this patient the path was adequate on one side as seen on this image. D, The patient was placed in skull tong traction and reduced. She was then taken to surgery for fixation using one C1-C2 transarticular screw combined with sublaminar cables from C1 to C2 combined with autogenous structural iliac bone graft. The patient’s fracture healed satisfactorily.

(Reproduced with permission from Eismont FJ, Currier BL, McGuire RA Jr: Cervical spine and spinal cord injuries: Recognition and treatment. In Helfet DL, Greene WB [eds]: Instructional Course Lectures, vol 53. Rosemont, IL, American Academy of Orthopedic Surgeons, 2003, p 346.)

FIGURE 76–19 This patient was involved in a motor vehicle collision and sustained trauma with multiple fractures including this type II odontoid fracture. A, Postinjury lateral radiograph shows the type II odontoid fracture, which appears well aligned but to have a significant gap in the posterior cortex of the odontoid. With this type of gap present between C1 and C2, it would usually not be possible to insert C1-C2 transarticular screws and obtain adequate purchase. B, This patient’s odontoid fracture was stabilized with C1 lateral mass screws combined with C2 pedicle screws. The starting point for the C1 lateral mass screw is just beneath the posterior arch of C1, and the anterior end point is the same as for C1-C2 transarticular screws. This screw-rod construct combined with C1-C2 wiring is able to provide adequate compression across the fracture site to achieve reduction and provide the best opportunity for fracture healing.

FIGURE 76–20 This patient was involved in a motor vehicle accident and sustained a type III odontoid fracture. She was neurologically normal. A, This midsagittal reconstructed computed tomography (CT) scan shows minimal displacement of the fracture. B, This postoperative radiograph shows good alignment of the odontoid fracture. This fracture was fixed with C1 screws and C2 translaminar screws. This was selected because of vertebral artery anomalies in the C2 vertebra. C, This open-mouth radiograph shows the C1 screws centered in each lateral mass, and the C2 screws are traversing side to side within the lamina. D, This postoperative transverse CT image at C1 shows ideal position of the C1 screws. E, This transverse CT image at C2 shows the screws within the lamina of C2. Using the C2 translaminar screws obviates concern over vertebral artery anomalies within the C2 vertebral body and pedicle.

Primary osteosynthesis of the dens (Fig. 76–21) has the theoretical advantage of preserving rotation at the atlantoaxial joint, but the amount of motion that is preserved over a C1-C2 fusion may not be significant.⁸⁷ To achieve successful anterior fracture fixation, the fracture needs to be transverse, noncomminuted, and reducible. The patient’s chest anatomy and odontoid anatomy must also be amenable to this technique. In the elderly, the use of odontoid screws is associated with a high complication rate.⁸⁸ Two large series of anterior odontoid screw fixation show failure rates of 13% to 17%.^89,90

FIGURE 76–21 This teenager fell from a moving vehicle and sustained a type II odontoid fracture. A, Scout film from the computed tomography (CT) scan shows that his odontoid process is displaced posteriorly more than 1 cm. The patient’s young age made anterior odontoid fracture fixation preferable to a posterior C1-C2 fusion. B and C, Midsagittal and coronal CT reconstruction images were taken at 3 months from the time of surgery. It can be seen that the fracture was well reduced and is now well healed. It is important that the cephalad portion of the screw penetrates through the cortex to gain optimal fixation.

Biplanar fluoroscopy or intraoperative CT with image guidance is essential for this technique.

Traumatic Spondylolisthesis of the Axis

Traumatic spondylolisthesis of the axis, also known as a hangman’s fracture, can be caused by a variety of mechanisms including combinations of extension, flexion, distraction, and axial loading of the cervical spine. The fracture line passes through the neural arch of the axis. These fractures are best classified using the modification of the Effendi classification system (Fig. 76–22).⁹¹ Type I fractures occur through the pars interarticularis bilaterally with less than 3 mm translation and no angulation. This fracture usually results from hyperextension and axial load. The neural arch fractures, but the intervertebral disc and anterior longitudinal ligament are still intact (Fig. 76–23). This fracture is associated with other extension-type injuries including C1 posterior arch fractures and dens fractures.

FIGURE 76–22 These illustrations demonstrate the classification of traumatic spondylolisthesis of the axis. A, Type I hangman’s fracture has fractures of the C2 pedicles bilaterally with no angulation and with as much as 3 mm of displacement. B, Type II fractures have both significant angulation and significant displacement. C, Type IIa fractures show minimum displacement but there is severe angulation, apparently hinging from the anterior longitudinal ligament. These fractures have disruption through the disc space and are easily overdistracted with even small amounts of traction. D, Type III hangman’s fracture combines bilateral facet dislocations between the second and third cervical vertebra with the fracture of the neural arch. This group of patients will always require surgery to reduce the dislocated facets.

(Reproduced with permission from Levine AM, Edwards CC: The management of traumatic spondylolisthesis of the axis. J Bone Joint Surg Am 67:217-226, 1985.)

FIGURE 76–23 This patient was involved in a motor vehicle accident and sustained a type I fracture of the pedicles of C2. He had no other injuries. A, Lateral radiograph taken immediately after injury shows minimal angulation and no significant displacement at the fracture site. The patient was treated in a rigid cervical collar for 8 weeks. B, There is adequate healing of the C2 fracture with good alignment of the spine.

(Reproduced with permission from Eismont FJ, Currier BL, McGuire RA Jr: Cervical spine and spinal cord injuries: Recognition and treatment. In Helfet DL, Greene WB [eds]: Instructional Course Lectures, vol 53. Rosemont, IL, American Academy of Orthopedic Surgeons, 2003, p 343.)

Type II fractures are bipedicular fractures with greater than 3 mm of displacement and angulation of C2 on C3. This fracture results from an initial axial load with hyperextension of the neck causing a fracture of the neural arch, followed by a flexion moment that results in disruption of the C2-C3 intervertebral disc. This is often accompanied by a compression fracture of the anterosuperior corner of C3 or the posteroinferior body of C2.⁹¹ Two variants of type II fractures have been described. The type IIA fracture shows significant angulation but has minimal (rarely exceeding 2 to 3 mm) translation and includes significant disruption of the disc and posterior longitudinal ligament. Gross disc space distraction occurs after the application of minimal amounts of traction (Fig. 76–24). This injury usually results from a flexion-distraction injury. In a type II variant described by Starr and Eismont, the fracture line propagates through the posterior aspect of the vertebral body with unilateral or bilateral continuity of the posterior cortex and is associated with a 33% incidence of neurologic deficit (Fig. 76–25).⁹²

FIGURE 76–24 This patient was involved in a motor vehicle collision and sustained this fracture of the pedicles of C2. She had no other significant injuries and she was neurologically intact. A, Lateral radiograph shows approximately 8 mm anterior subluxation with C2 anteriorly displaced on C3. The angulation of C2 on C3 is quite minimal. One would suspect the disc at C2-C3 is completely disrupted, however, because of the severe degree of displacement. This is also consistent with the large amount of anterior soft tissue swelling in front of C3, which measures 40 mm. B, The patient was placed in 5 lb of traction. Overdistraction at the C2-C3 disc space is apparent. The patient remained neurologically intact. C, The patient’s traction was discontinued, and a halo vest was applied. Reduction was achieved under fluoroscopy. The patient remained neurologically normal. She was mobilized more slowly than most patients because of the instability that was present. D, A lateral radiograph taken 3 months after her injury shows that the soft tissue swelling is completely resolved. There is calcification anteriorly at the C2-C3 disc space. This is often seen with these injuries owing to the significant amount of anterior striping of the anterior longitudinal ligament from the anterior aspect of the C3 vertebral body. With an anterior C2-C3 spontaneous fusion, posterior healing at the pedicles is unimportant.

FIGURE 76–25 This patient sustained a C2 pedicle fracture as a pedestrian when struck by a car. He had sustained an incomplete quadriplegia noted at the time of the accident. A, Lateral radiograph shows mild to moderate anterior displacement of C2 on C3. By looking at the posterior aspect of the C2 vertebral body, it is apparent that there is a fracture with part of the C2 vertebral body staying in line with the C3 vertebral body, but there is also a fracture line just above this showing anterior displacement of the more cephalad aspect of the axis. B, Computed tomography scan shows that the fracture line involved the posterior aspect of the vertebral body on the right side. This patient was treated in a halo vest and had complete resolution of his paralysis and his C2 fractures healed. His spine was stable when seen at follow-up.

Type III hangman’s fractures are unstable injuries with severe displacement and angulation, associated with unilateral or bilateral facet dislocations of C2 on C3. Disruption of the posterior longitudinal ligament and the C2-C3 intervertebral disc occurs in these injuries. These injuries are commonly associated with neurologic injuries. Type III injuries occur in three basic patterns: bilateral neural arch fractures anterior to the facet joints with bilateral facet dislocations posterior to it; a rotational injury with fracture of the neural arch on one side anterior to the facet joint and on the second side in the area of the facet joint causing a unilateral facet dislocation; and a bilateral facet dislocation with fractures of the neural arch just posterior to the facet joints. Type III injuries are usually the result of flexion-distraction followed by hyperextension.

Isolated type I fractures can be treated in a rigid cervical collar for 8 to 12 weeks. Type II fractures are treated with initial traction in extension followed by immobilization in a halo vest. Type IIa fractures are treated with immediate application of a halo vest. Traction is avoided in patients with type IIa injuries because even minimal traction can cause severe overdistraction. All type III fractures should be treated with surgical reduction and posterior C2-C3 fusion. Internal fixation can be achieved with posterior pedicle screws at C2 into the C2 vertebral body and lateral mass screws at C3.

Nonunions of type II or IIa injuries are uncommon,⁹³ but if they occur and are symptomatic, they can be treated with either a posterior C1 to C3 fusion or an anterior C2-C3 fusion.