Biomechanical effects of C2-C7 intersegmental stability due to laminectomy with unilateral and bilateral facetectomy.

STUDY DESIGN The biomechanical responses resulting from laminectomy with graded unilateral and bilateral facetectomy were quantified using a three-dimensional nonlinear finite element model of the C2-C7 motion segments. OBJECTIVE To study the influence of laminectomy with graded unilateral and bilateral facetectomy on the cervical spinal biomechanics. SUMMARY OF BACKGROUND DATA Cervical spinal stenosis is a condition that is caused by the narrowing of the spinal canal. Laminectomy and facetectomy are commonly used surgical procedures for decompressing cervical spinal stenosis. Resection of the posterior structures causes instability and affects the internal stresses of the cervical spinal components. However, the influence of these surgical procedures on the biomechanical responses of the cervical spine has not been studied. METHODS A nonlinear finite element model of the intact C2-C7 was constructed and validated. Ten surgically altered models were created from the intact model and were tested under physiologic loading. Because of the inclusion of five motion segments, it was possible to determine the intersegmental responses and internal cortical shell and disc stresses in the adjacent altered and unaltered spinal components. RESULTS Under combined flexion and extension, intersegmental motions at C4-C5 and C5-C6 increased significantly after C5 laminectomy. Subsequent facetectomy performed at C5 and C6 on the laminectomized model only affected the responses at the C5-C6 segment. Overall, slight intersegmental responses of up to 5% were observed at the adjacent levels of C3-C4 and C6-C7. Laminectomy did not cause any significant increase in the intersegmental motions under lateral bending and axial rotation. Extending the surgical procedures to unilateral and bilateral facetectomy only increased the intersegmental motions slightly. Similar increases in the intervertebral disc and the cortical shell stresses were observed. These findings may partially explain the clinical observations of enhanced osteophytes formation. CONCLUSIONS This study provides a better understanding of the surgically altered cervical spinal biomechanics and may help formulate treatment strategies such as spinal implants.