Cervical stability after sequential capsule resection.

A portion of the cervical facet joint must be resected to expose and decompress cervical nerve roots from a posterior approach. When posterior fusion is performed, it is common to remove the facet capsule only for the joints being fused. This study was performed to examine the effect of resection of the facet capsule alone, without disruption of the bony facet to determine what degree of facet-capsule resection leads to acute instability. Seven human cervical cadaveric spines were used in the experiment. Nondestructive biomechanical testing was performed in axial load, flexion, extension, and torsion. Each specimen was tested intact and after sequential resection of 25%, 50%, 75%, and 100% of the C5-6 facet capsules. Axial stiffness changed very little during the experiment. In torsion, the displacement increased 1% after a 25% capsule resection, 19% after a 50% resection, and 25% after a 75% or 100% resection. No gross subluxation was seen during the torsional test. In the flexion test, posterior displacement increased 4% after a 25% resection, 5% after a 50% resection, 32% after a 75% resection, and 22% after a 100% resection. There was a statistically increased displacement seen during the flexion test after 75% or 100% of capsule resection. Thus, significant hypermobility did occur during both torsion and flexion testing with greater than 50% resection of the facet capsules. Great care should be taken when exposing an unfused facet to limit facet-capsule resection to less than 50%. With resection of greater than 50% of the capsule, postoperative hypermobility can occur and may require stabilization.