Posterior Cervical Stabilization Techniques: Cervical Pedicle Screw Fixation, Lateral Mass Screw Fixation, and Wiring

Overview

A variety of techniques have been developed to internally stabilize the subaxial cervical spine using a posterior approach. These include interspinous wiring with bone grafts, interlaminar clamps, hook plates, lateral mass screw and plates or rod and pedicle screw, and rod constructs. Before the advent of lateral mass screw fixation, intraspinous wiring was commonly used for multilevel subaxial cervical stabilization. For cases requiring laminectomy with removal of the spinous process, various facet wiring techniques were developed, with and without bone grafting, for stabilization purposes.

In the late 1970s, Roy-Camille presented a technique for posterior cervical fixation in which plates were secured to the lateral masses using screws, a technique proven by biomechanical test results to be significantly stronger than previous constructs. Application of this technique in cervical trauma cases resulted in fusion rates greater than 95% when autogenous bone grafting was combined. Because lateral mass screws at C7 often achieve inadequate purchase, pedicle fixation of the lower cervical spine and upper thoracic vertebrae has been proposed. Transpedicular screws have been shown to have more fixation stability than other subaxial cervical spine reconstruction systems. However, because pedicle screw fixation has the potential to seriously injure the spinal cord, nerve roots, or vertebral arteries, it is generally considered a high-risk procedure. Nevertheless, if the safety of the procedure can be ensured, cervical pedicle screw fixation is an effective procedure for reconstructing the cervical spine.

In this chapter, we introduce the posterior cervical stabilization techniques of cervical pedicle screw fixation, lateral mass screw fixation, and wiring for the treatment of an unstable cervical spine, and we describe indications, procedural steps, intraoperative imaging techniques, technical pitfalls, and postoperative courses in detail.

Cervical Pedicle Screw Fixation

Cervical pedicle screw fixations have more fixation stability than other subaxial cervical spine reconstruction systems. Therefore this procedure is especially beneficial in settings where laminae or lateral masses may be inadequate because of postsurgical disturbances or marked osteoporosis. Preoperative evaluation of the vertebral artery and pedicle is critically important for cervical pedicle screw fixation; therefore preoperative computed tomographic angiography (CTA) or magnetic resonance angiography (MRA) is required.

Indications

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Cases that require powerful correction of cervical kyphosis
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Progressive symptomatic cervical myelopathy that requires surgical decompression and fusion
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Cervical instability—traumatic, iatrogenic, neoplastic, or inflammatory—with disruption or destruction of the posterior elements that precludes the use of standard fixation
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Fixation for C2 and C7
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Following a multiple-level anterior cervical decompression and fusion for added stability

Contraindications

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Patients with insufficient pedicles (congenitally narrow pedicles <4.5 mm in diameter)
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Destruction of pedicles by trauma/tumor
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Ipsilateral to a single dominant vertebral artery with the contralateral side nonfunctional
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Ipsilateral to an anomalous vertebral artery

Operative Technique

Patient Positioning and Incision

The patient is placed in a prone position with the skull fixed in a Mayfield three-point fixator and the cervical spine positioned parallel to the floor ( Fig. 22-1 ). Both shoulders are pulled caudally and fixed by taping. A midline posterior approach is used, and longitudinal midline exposure through the ligamentum nuchae is performed. Monopolar electrocautery is used to dissect down to and through the ligamentum nuchae. Strict subperiosteal dissection makes a bloodless operation field, and care should be taken not to disrupt the attachments of the semispinalis cervicis and capitis to C2, which can lead to increased risk of C2 on C3 kyphosis.

Adequate exposure of the lateral mass is crucial for accurate screw placement ( Fig. 22-2 ). Care should be taken to avoid violating the facet capsules of levels not intended to be fused. Dissection lateral to the lateral aspect of the articular pillars can lead to excessive venous bleeding. If adequate exposure of the surgical field cannot be obtained, an additional small incision lateral to the main incision can be considered.

Subaxial Pedicle Screw Insertion

Accurate screw placement requires precise identification of the screw entry point matched with the trajectory angle. For that purpose, four techniques can be used: 1) the original technique described by Abumi and colleagues, 2) pedicle axis view by fluoroscopy, 3) the laminoforaminotomy technique, and 4) computer-assisted navigation techniques ( Figs. 22-3 and 22-4 ). Computed tomography (CT) allows the assessment of pedicle morphology and dimensions and allows the surgeon to determine the appropriate screw diameter, length, and transverse plane trajectory.

The points of screw penetration for the C3 through C7 pedicles are slightly lateral to the center of the lateral mass and close to the inferior margin of the inferior articular process of the upper adjacent vertebra ( Fig. 22-5 ). The lateral margin of the lateral mass of the cervical spine has a notch approximately below the lateral vertebral notch at C2 and C3–C6 and at or slightly above the notch at C7.

The drill is angled 45 degrees medially and is advanced in a vertical line parallel to the end plate (see Fig. 22-5 ). Alternatively, a line parallel to the contralateral lamina provides a 3-mm safe corridor for sagittal plane angulation. Another option is removal of the lateral mass with a high-speed burr to provide a direct view of the pedicle introitus. The pedicle is probed and tapped, and a 3.5-mm cortical screw is inserted (see Fig. 22-5 ). Mean pullout strengths are similar. Standard angulations and entry points may be dangerous, because pedicle anatomy and surface topography are highly variable between C4 and C6.

Pedicle screw fixation safety can be improved by avoiding pedicles smaller than 45 mm, by performing a laminoforaminotomy to palpate the pedicle directly, and/or by using navigation assistance. Violation of the upper facet capsules sometimes causes instability. Cervical roots run just above the pedicles, unlike in the lumbar spine. Cephalad malpositioning of pedicle screws is more likely to cause root injury than caudal malpositioning.

Intraoperative electromyography assessment may be helpful for posterior cervical screw placement. To reduce scatter, the screws should be tested before placing the connecting rod. Stimulation thresholds correlate with screw position, and values greater than 15 mA reliably predict acceptable screw positioning.

Fusion

Facets of the segments to be fused are drilled to remove joint material. Lateral mass bone is then decorticated with a high-speed cutting burr and irrigation, with care taken not to create thermal injury that will inhibit bone fusion. Morcellized autograft harvested from the posterior iliac crest is filled into the decorticated facet joints and is packed along the decorticated lateral mass bone. Local autograft from the cervical decompression with or without demineralized bone matrix may also be used.

Wound Closure

A suction drain is inserted, and the deep fascial sutures are tied down. Subcutaneous sutures are then used, followed by staples for the skin.

Postoperative Management

Postoperative immobilization varies according to the number of fixed spinal segments, the patient’s general condition, the stability of the inserted screws, the extent of osteoporosis, and other factors.

Generally, patients who required fixation of one to three motion segments are required to wear a short, soft neck collar postoperatively for 2 to 3 weeks. A Philadelphia collar should be worn for 2 to 3 months by patients with severe osteoporosis and those who underwent fixation of four or more motion segments. More rigid postoperative external supports, including halo–vest immobilization, are not typically used. All patients are permitted to ambulate or sit upright in bed the day after surgery unless contraindicated by their general condition. Patients with jobs that have low physical demands can return to their original jobs 3 to 6 weeks after surgery, before bony union is complete.

Complications

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Vertebral artery injury from a laterally perforated screw
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Penetration of the pedicle
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Radiculopathy as a result of nerve root injury from a cranially or caudally dislodged screw
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Dural injury or spinal cord injury from a screw that strays out medially

Surgeons must bear in mind that cervical pedicle screw placement is limited by anatomic variation of the pedicle and the vertebral artery. Complications can be minimized by sufficient preoperative imaging studies of the pedicles, thorough knowledge of local anatomy, and strict control of intraoperative maneuvers for screw placement.

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