The effects of implant stiffness on the bypassed bone mineral density and facet fusion stiffness of the canine spine

Study Design. Effects of spinal implant stiffness and removal/retention on bypassed bone mineral density and column/fusion stiffness were studied in dogs. Methods. After facet fusion and bicortical peripedicle screw placement, one group of eight dogs received 6.35 mm and another 4.76 mm rod instrumentation at L3-L5. At 12 weeks, four in each group had implants removed. Bone mineral density was analyzed by dual energy x-ray absorptiometry at 1 to 24 weeks. Axial compressive stiffness of the L3-L5 construct, spinal column, fused facets, and instrumentation were measured. Percent load through the vertebral column was predicted