Cervical spine strength after facet injury and spine plate application

Although metallic plates are used for cervical spine stabilization, few biomechanical studies have been done to evaluate their efficiency. A previous study indicated that one half of the facet joint may be destroyed before compromise in strength occurs. Isolated motion segments in which one half of the facet joint was resected bilaterally were used. A two-hole Roy-Camille plate was attached bilaterally with 3.5-mm-diameter, 16-mm-long screws and the construct loaded in shear. Failure occurred at 415.6 N by fracture through the screw holes of the damaged joint, compared to a failure load of 699.6 N in specimens without screws and plates but in which 75% of the joint had been destroyed. Results were significant at the 95% confidence level. A second group of specimens using C2-3-4 and C5-6-7 was tested after 50% facet resection and application of a three-segment plate. Failure again occurred by fracture through the screw hole at the damaged joint. We conclude that, if significant facet destruction is present, screw holes for plate application further weakens the bone. The desired biomechanical stability may not be present.