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

采用脊柱骨折和畸形模型，进行生物力学和临床研究，评价脊柱内固定的稳定性和对残存完整运动节段的影响。传统的硬质金属脊柱内固定在脊柱骨折和畸形模型上都提供了有效的满足性。然而，随着内固定刚度的增加，相邻完整运动节段上的应力显著增加。此外，脊柱内固定改变了残余运动节段的运动模式，并且随着固定刚度的增加，运动模式的变化变得更加明显。为了克服传统金属内固定的这些负面影响，研制了一种由金属螺丝钉和PLLA棒组成的新型脊柱内固定系统用于实验研究。用PLLA器械对12只绵羊进行腰椎融合术。共24个脊柱节段进行融合。4~6个月后，虽然PLLA在活体中溶解，但腰椎运动节段被处死，提取的PLLA棒没有溶解的证据。为了使PLLA植入物足够稳定，以承受脊柱必须承受的负荷，PLLA的溶解能力将被牺牲。目前，具有足够稳定性以重建脊柱，同时具有溶解特性以允许脊柱节段有效融合的PLLA器械很难开发出来。开发新的系统还需要进一步的研究。临床应用PLLA螺丝钉将植骨固定到植骨部位，重建颈椎疾患。我们分析了30多名接受颈椎融合术的父母。所有患者均获得了牢固的融合，并显示出比单纯植骨而不使用PLLA螺钉固定更好的临床效果。

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.