Occipitocervical Fixation

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Chapter Synopsis	Occipitocervical fixation techniques have evolved significantly from early occipitocervical wiring techniques to the current rod-screw-occipital plate constructs. Indications for occipitocervical fixation include traumatic injuries, congenital malformations, rheumatoid arthritis, and oncologic processes involving the craniovertebral junction. Judicious clinical decision making and meticulous surgical technique are necessary to manage patients requiring occipitocervical fixation.
Important Points	Surgical indications Imaging findings Surgical techniques
Clinical and Surgical Pearls	Construct selection should be based on individual anatomic considerations. Proper occipitocervical head position should be confirmed before fixation. Image guidance should be considered in cases of abnormal anatomy. Preoperative vascular imaging should be obtained in cases of abnormal anatomy. Proper C1 lateral mass screw length should be ensured to facilitate rod placement. The surgeon should consider using rib (versus iliac crest) autograft to reduce donor site morbidity. Proper wiring techniques should be used to secure the allograft construct.
Clinical and Surgical Pitfalls	Fixation in excessive flexion or extension can result in swallowing difficulty or poor visualization of the ground, or both. Improper identification of the keel or midline for occipital screw placement can result in cerebellar screw violation. Inadequate occipital screw tapping can result in loose occipital screws. High-riding or proud occipital instrumentation can result in hardware erosion. C1 lateral mass or C2 pedicle screw misplacement can result in vertebral artery injury. Image guidance should be used when the anatomy is mobile.

Occipitocervical fixation (OCF) is a maximally invasive surgical technique that results in significant loss of flexion, extension, and rotation. Therefore, surgical indications for OCF are either conditions that result in cervicomedullary compression, the treatment of which would cause instability, or entities that themselves result in overt instability at the occipitocervical junction. These surgical indications include traumatic injuries, rheumatoid arthritis (RA), congenital malformations, and primary and metastatic neoplastic lesions of the craniocervical junction. The earliest description of occipitocervical fusion was by Foerster in 1927. In subsequent decades, additional reports described similar bone onlay techniques. Occipitocervical techniques have evolved extensively since their initial description, and competent spine surgeons should possess a mastery of these techniques in their surgical armamentarium.

Preoperative Considerations

Traumatic Injuries of the Craniovertebral Junction

Traumatic injuries of the craniovertebral junction include occipitoatlantal dislocation (OAD), occipital condyle fractures, atlas fractures, and axis fractures and dislocations.

Occipitoatlantal Dislocation

Considerable force is required to cause OAD, and patients often present with significant head, spinal cord, or multisystemic traumatic injuries. Mechanical ventilation, which can be needed as a result of brainstem compromise, often makes neurologic assessment difficult. Cranial nerve deficits or vertebral artery injury can be present. Despite the significant nature of the injury, some patients may have no neurologic deficits.

Once OAD is suspected based on examination or mechanism of injury, strict cervical spine precautions are mandatory to prevent further complications. Sandbags should be used for initial head immobilization because rigid cervical collars can further distract the occipitoatlantal joint. The authors agree with other investigators who recommend early halo fixation once the diagnosis of OAD is confirmed. Even if surgical fixation is planned, a halo vest minimizes motion of the cervical spine during intubation and positioning.

A wide range of sensitivities has been reported for the techniques used to diagnose OAD, and none of these criteria is fail proof. Available methods include the Power ratio, the X-line method, the condylar gap method, the basion-dens interval (BDI), and the basion-axial interval (BAI). A universal theme underlying the difficulties of diagnosing OAD using plain lateral cervical radiographs is the ability to visualize the anatomic landmarks required for application of these methods. Dedicated studies using computed tomography (CT) to diagnose OAD have supported the use of the BDI (with 10 mm as the cutoff) and the occipital condyle–C1 interval (CCI) (>4 mm is abnormal) as the diagnostic tests of choice.

The increased use of magnetic resonance imaging (MRI) in trauma patients raises the question of how to interpret equivocal findings in the occipitoatlantal region. The primary dilemma is how to treat patients with equivocal occipitoatlantal joint disruptions noted on MRI whose measurements on CT are normal. Further research may uncover a less severe but still unstable occipitoatlantal joint injury that threatens the neural structures enough to warrant internal fixation of the occiput to the cervical spine.

Once the diagnosis of OAD has been established, OCF is the appropriate treatment. Contraindications to treatment include medical instability in patients.

Occipital Condyle Fractures

The initial neurologic evaluation of patients presenting with occipital condyle fractures is often confounded by a concomitant head injury. Other patients can become symptomatic with neurologic injury or just neck pain. CT of the cervical spine is critical in diagnosing these fractures, which are often missed on plain radiographic imaging. Most isolated occipital condyle fractures can be treated with either a hard collar or halo immobilization. Surgical intervention is indicated in cases of concurrent ligamentous injury and instability on dynamic imaging.

Atlas and Axis Fractures

Patients with atlas fractures often present with neck pain, although symptoms can include difficulty swallowing related to retropharyngeal edema or neurologic deficit related to vertebral artery injury or lower cranial nerve injury. Although plain radiographs can detect an atlas fracture, fine-cut CT with sagittal and coronal reformatted scans can rule out pseudospread of the atlas, and MRI can be used to evaluate the integrity of the transverse ligament. Surgical fixation is rarely indicated for isolated C1 fractures. C1 fractures associated with C2 fractures demonstrating dynamic instability, an atlantodens interval (ADI) greater than 5 mm, more than 11 degrees of C2-C3 angulation, or an incompetent transverse ligament may require OCF. Isolated axis fractures rarely require OCF.

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