The destabilizing effect of cervical foraminotomy - an ex vivo biomechanical study.

Background Context Posterior cervical foraminotomy is a minimally invasive, motion-preserving treatment for cervical radiculopathy. However, surgeons still rely on the traditional "50% rule" for facet resection despite limited biomechanical evidence supporting this threshold. Purpose To evaluate the biomechanical effects of graded unilateral facet joint resection (10%, 25%, 50%, 75%, 100%) compared with the native state. Study Design Cadaveric biomechanical study Methods Nine cervical segments from five fresh-frozen cadavers were tested under load control. Segmental ROM was assessed in the native state and after 10%, 25%, 50%, 75%, and 100% facet resection in flexion-extension (FE), lateral shear (LS), lateral bending (LB), anteroposterior shear (AS), and axial rotation (AR). Results ROM increased in all directions with progressive facet (and adjacent capsular) resection. Significant changes were observed at 25% resection (native vs. 25%): AR, 1.8° vs. 2.7°; FE, 7.1° vs. 8.6°; and LS, 0.6 mm vs. 0.6 mm (all p<0.05). Beyond 50% resection, FE, LS, and AS largely plateaued. AR showed the greatest increase in ROM, reaching 45% and 71% above the native condition after 75% and 100% resection, respectively (p<0.05). Conclusion Unilateral cervical foraminotomy caused progressive, motion-specific destabilization, most pronounced in AR, followed by LB. Significant changes occurred within the first 25% of resection. Beyond 50%, FE, LS, and AS plateaued, whereas AR continued to increase without a discrete threshold. Clinical significance: These findings support minimizing facet and capsular disruption and challenge the 50% rule as a universal biomechanical safety threshold.