Adjacent-level range of motion and intradiscal pressure after posterior cervical decompression and fixation: an in vitro human cadaveric model.

STUDY DESIGN

This in vitro human cadaveric study measured adjacent-level kinematics after posterior cervical decompression and fixation.

OBJECTIVE

Quantify adjacent-level changes in range of motion (ROM) and intradiscal pressure after posterior cervical decompression and fixation.

SUMMARY OF BACKGROUND DATA

Optimal length of instrumentation after posterior decompression is unclear. Longer posterior cervical fixation constructs may increase the risk of adjacent-segment degeneration.

METHODS

Eight cervicothoracic spines were evaluated intact, with C3-C6 laminectomy, C3-C6 laminectomy + C3-C6 fixation, C3-C6 laminectomy + C3-C7 fixation, C3-C7 laminectomy, C3-C7 laminectomy + C3-C7 fixation, C3-C7 laminectomy + C2-C7 fixation, C3-C7 laminectomy + C3-T2 fixation, and C3-C7 laminectomy + C2-T2 fixation. Testing included intact moments (± 2.0 N·m) in flexion/extension, axial rotation, and lateral bending, with quantification of ROM at C2-C3, C6-C7, and C7-T1 normalized to the intact spine. Intradiscal pressures were also measured at each level.

RESULTS

For the C3-C6 laminectomy group, there were no differences in adjacent-level flexion/extension ROM or intradiscal pressure based on construct length, except at C6-C7, where ROM was significantly decreased when fixation was extended to C7 (P < 0.05). After C3-C7 laminectomy and reconstruction, the greatest increase in C2-C3 flexion/extension ROM and intradiscal pressure occurred in the C3-T2 fixation subgroup (ROM: 348% [P < 0.05]; intradiscal pressure: 319 ± 243 psi [pounds per square inch] vs. 65 ± 41 psi intact [P < 0.05]). At C7-T1, the greatest increase in flexion/extension ROM and intradiscal pressure occurred after C2-C7 fixation (ROM: 531% [P < 0.05]; intradiscal pressure: 152 ± 83 psi vs. 21 ± 14 psi intact [P < 0.05]).

CONCLUSION

For C3-C6 laminectomy, instrumentation to C7 significantly decreased flexion/extension ROM and intradiscal pressure at C6-C7 without significantly increasing either measure at C2-C3 or C7-T1 relative to C3-C6 fixation. In the setting of a C3-C7 laminectomy, when instrumenting to either C2 or T2, consideration should be given to including both levels within these constructs.