Accuracy of cervical pedicle screw placement using the funnel technique.

STUDY DESIGN: This was a cadaver study assessing the accuracy of cervical pedicle screw placement. OBJECTIVE: To evaluate the accuracy of the funnel technique of screw placement. SUMMARY OF BACKGROUND DATA: Although excellent results have been reported in clinical studies, with no major neurovascular injuries, several cadaveric studies have shown a high pedicle perforation rate during screw placement. METHODS: Ten fresh frozen cervical spines (C2-C7) were used (120 pedicles, 20 pedicles per level). The average specimen age was 79.6 years (range 65-97); the average height was 159 cm (range 155-175). The male-to-female ratio was 3:7. Pedicle width and angulation were measured on preoperative axial computed tomography (1-mm slices). By use of four bony landmarks and the funnel technique, screws were placed under direct vision. Critical perforations (documented contact of a screw with, or an injury to, a spinal cord, nerve root, or vertebral artery) and noncritical perforations (a perforation with no critical contact) were recorded. RESULTS: In seven pedicles (5.8%) the procedure was aborted because of a small or nonexistent pedicle medullary canal. Ninety-four pedicle screws (83.2%) were placed correctly, whereas 11 pedicles (9.7%) had noncritical perforations and 8 pedicles (7.1%) had critical perforations. The majority of the critical and noncritical perforations were at C3, C4, and C5. CONCLUSIONS: Axial computed tomography is necessary for the preoperative planning. Because of the small diameter and steep angulation of cervical pedicles, every spine surgeon who intends to use pedicle screws should first master the technique on cadavers.

Successful short-segment instrumentation and fusion for thoracolumbar spine fractures: a consecutive 41/2-year series.

STUDY DESIGN: A retrospective review of all the surgically managed spinal fractures at the University of Missouri Medical Center during the 41/2-year period from January 1989 to July 1993 was performed. Of the 51 surgically managed patients, 46 were instrumented by short-segment technique (attachment of one level above the fracture to one level below the fracture). The other 5 patients in this consecutive series had multiple trauma. These patients were included in the review because this was a consecutive series. However, they were grouped separately because they were instrumented by long-segment technique because of their multiple organ system injuries. OBJECTIVES: The choice of the anterior or posterior approach for short-segment instrumentation was based on the Load-Sharing Classification published in a 1994 issue of Spine. The purpose of this review was to demonstrate that grading comminution by use of the Load-Sharing Classification for approach selection and the choice of patients with isolated fractures who are cooperative with spinal bracing for 4 months provide the keys to successful short-segment treatment of isolated spinal fractures. SUMMARY OF BACKGROUND DATA: The current literature implies that the use of pedicle screws for short-segment instrumentation of spinal fracture is dangerous and inappropriate because of the high screw fracture rate. METHODS: Charts, operative notes, preoperative and postoperative radiographs, computed tomography scans, and follow-up records of all patients were reviewed carefully from the time of surgery until final follow-up assessment. The Load-Sharing Classification had been used prospectively for all patients before their surgery to determine the approach for short-segment instrumentation. Denis' Pain Scale and Work Scales were obtained during follow-up evaluation for all patients. RESULTS: All patients were observed over 40 months except for 1 patient who died of unrelated causes after 35 months. The mean follow-up period was 66 months (51/2 years). No patient was lost to follow-up evaluation. Prospective application of the Load-Sharing Classification to the patients' injury and restriction of the short-segment approach to cooperative patients with isolated spinal fractures (excluding multisystem trauma patients) allowed 45 of 46 patients instrumented by the short-segment technique to proceed to successful healing in virtual anatomic alignment. CONCLUSIONS: The Load-Sharing Classification is a straightforward way to describe the amount of bony comminution in a spinal fracture. When applied to patients with isolated spine fractures who are cooperative with 3 to 4 months of spinal bracing, it can help the surgeon select short-segment pedicle-screw-based fixation using the posterior approach for less comminuted injuries and the anterior approach for those more comminuted. The choice of which fracture-dislocations should be strut grafted anteriorly and which need only posterior short-segment pedicle-screw-based instrumentation also can be made using the Load-Sharing Classification.

Surgical anatomy of the cervical pedicles: landmarks for posterior cervical pedicle entrance localization.

The posterior entrance to the cervical pedicle is described using quantitative and descriptive parameters. Fifty-three spines (C2-C7) were evaluated using a digital caliper and by visual inspection using four bony landmarks: the lateral vertebral notch and inferior articular process (C2-C7), the medial pedicle cortex at C2, and the transverse process at C7. Three distances were defined. (1) At C2, the average medial pedicle cortex-pedicle distance was 7.2 mm. (2) The lateral vertebral notch-pedicle distances showed that the entrances were located close to the notch at C2, almost at the notch at C3 and C4, and gradually moved medially away from the notch from C5 to C7. The pedicles were rarely located lateral to the lateral vertebral notch. (3) The inferior articular process-pedicle distance was large at C2, the shortest at C3, and gradually increased toward C7. Three relations were defined. (1) The pedicles were located mostly in the intermediate third of the inferior facet at C2; in the lateral third at C3, C4, and C7; or in the lateral or intermediate thirds at C5 and C6. Only C2 and C6 pedicles were located in its medial third. (2) The pedicles were located mostly below the lateral vertebral notch at C2, at C3-C6, or almost equally above and at the notch at C7. (3) Most of the C7 pedicles were located below the midline of the transverse process. The location of the pedicle entrance was unique at each cervical level. Their distribution followed the cervical spinal cord enlargement. These landmarks should assist with safe placement of pedicle screws.

Morphologic characteristics of human cervical pedicles.

STUDY DESIGN: Cervical pedicle morphology was investigated using manual and computed tomography measurements. OBJECTIVES: Normal anatomic variations of the cervical pedicles were measured to evaluate their safety as anchors for posterior cervical fixation systems. SUMMARY OF BACKGROUND DATA: There have been no cervical pedicle measurements on a large number of specimens. No study has ever measured the inner pedicle diameter. METHODS: Fifty-three spinal columns (C2-C7) of Euro-American origin identified by age, sex, and height (318 vertebrae or 636 pedicles) were measured using a digital caliper, a goniometer, and computed tomography scanning. RESULTS: The pedicle axis lengths were similar from C3 to C7 (except for shorter C2 pedicles). In the horizontal plane, the medial inclination of the pedicles followed the cervical spinal cord enlargement. In the sagittal plane, the pedicles were directed superiorly in the upper spine and inferiorly in the lower cervical spine. Some pedicles had no medullary canal (i.e., were solid cortical bone: 0.9% C2, 2.8% C3 and C4, and 3.8% C5 pedicles). The outer pedicle width was smaller than the height in most of the pedicles. The inner pedicle width was equal to or smaller than 2 mm in 13.2% C2, 72.6% C3, 67.0% C4, 62.3% C5, 51.9% C6, and 16.0% C7. The outer pedicle width was equal to or smaller than 4 mm in 8.5% C2, 75.5% C3, 35.8% C4, 13.2% C5 and C6, and 6.6% C7 pedicles. The thinnest pedicle cortex was always the lateral cortex, which protects the vertebral artery. Measurements of the posterior pedicle projection also were taken. CONCLUSIONS: These data provide anatomic limitations to pedicle screw use in the cervical spine.