Investigative study of Spinal Instrumentation utilizing PLLA (Poly-L-lactide)

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Biomechanical and clinical studies were performed to evaluate the stability and the influence of spinal instrumentation on the residual intact motion segments using spinal fracture and deformity models. Conventional rigid metal based spinal instrumentation provided effective satiability to the spine in both fracture and deformity modeles. However, as the rigidity of the instrumentation increased stress on the adjacent intact motion segments significantly increased. Also, spinal instrumentation changes the motion pattern of the residual motion segments, and the changes in the motion pattern become more distinct as the rigidity of the fixation increases. To overcome these negative effects of the conventional metal based instrumentation, new spinal instrumentation consists of metal screws and PLLA rod was developed for experimental investigation. Spinal fusion using PLLA instrumentation was performed in lumber spine of the 12 sheep. Total 24 spinal segments were fused. After four to six months, lumbar motion segments were sacrificed Although PLLA dissolves in the living body, extracted PLLA rods showed no evidence of dissolution. To make PLLA implant stable enough to withstand the load which spine must endure, dissolution ability of the PLLA will be sacrificed. At present technology, PLLA instrumentation which has enough stability to reconstruct the spine and, also, dissolution characteristic to allow effective fusion of the spinal segments is difficult to develop. Further research is required to develop new system. In clinical situation, the authors used PLLA screw for fixation of the bone graft to the graft site in reconstruction of the cervical spine disorders. We have analyzed more than 30 parents who underwent cervical fusion surrey. All patients obtained solid fusion and showed better clinical results compared to only graft without PLLA screw fixation.