Summary of Background Data: Laminectomy with screw-rod fixation is a common surgical procedure for unstable spinal column and assorted spinal disorders. The fixation provides strong stabilization at the cost of spinal normal motion. The immobilization of fused motion segment may induce the motion compensation at the adjacent level and then cause early degeneration. The dynamic stabilization system, a flexible spinal fixation device, is designed to preserve the normal spinal motion and avoid adjacent level degeneration. However, cases of adjacent level degeneration after dynamic stabilization are reported, which indicates the current stabilization system may still be too rigid. The ultimate flexibility for the dynamic stabilization system is not yet concluded. The purpose of this study is to find the variation of motion compensation and intradiscal pressure (IDP) in adjacent motion segment at different extent of fixation constraint.
Materials and methods: Eight 4-level lumbar motion segments were dissected from 6-month old pigs. A home-made dynamic spinal stabilizer was designed to control the range of motion (ROM) of the implanted motion segment. This stabilizer is able to control the ROM of motion segment by adjusting the block and shaft for linear and rotary constraints. The ROM of total and individual level of intact and injured lumbar spine under 6 Nm flexion and extension pure moment were first calculated from the motion of flags attached to the vertebrae. The injury was created by damaging the mid level bilateral facet joints and surrounding ligaments. After the injury, the injury level was implanted by a tradition rigid fixation device. Then, an angular displacement controlled rotation was applied to find the individual level ROM. The magnitude of angular rotation is the one of total ROM recorded at injury condition. The difference of ROM of mid level at injury and rigid fixed conditions was divided into 9 internals. Then, the home-made dynamic stabilizer was implanted to tune the ROM of mid level to these 9 intervals at the same displacement controlled rotation. The ROM and IDP in mid and adjacent cranial level of all setting were recorded.
Results: During the flexion, after the facet injury, the ROM of mid level increased from 4.0 (SD 0.8) to 8.0 (SD 2.3) degree, but the ROM of adjacent level remained similar. The loading conditions for the rigid and the 9 stabilization constraints were 17.2 (SD 3.4) and 9.7 (SD 1.2) degree for flexion and extension angular displacement control. After the rigid fixation, the ROM of mid level decreased to 2.4 (SD 0.7) degree, but the ROM of adjacent level was compensated (i.e., increased) to 6.7 (SD 1.7) degree. As the ROM of mid level increased with the loose of stabilizer, the ROM of adjacent level decreased. It was found that, the ROMs of mid level and adjacent level were similar when the stabilizer was set from 40% to 80% looseness. During the extension, the trend was similar to the one during extension, except that the ROMs of mid level and adjacent level were similar when the stabilizer was set from 30% to 60% looseness. For an intact motion segment, the IDP of mid level and adjacent level were 0.86 (SD 0.79) bar and 0.98 (SD 1.73) bar during 6 Nm extension, and were 6.29 (SD 2.61) bar and 6.27 (SD 1.12) bar during 6 Nm flexion. The injury of posterior elements significantly increased the IDP of injury level to 6.18 (SD 2.81) bar (p=0.003) during 6 Nm extension, but less affected the IDP of adjacent level. The posterior injury did not affect the IDP of injury level and adjacent level during flexion. The rigid fixation reduced the IDP of implanted level and adjacent level of injured spinal column to 1.59 (SD 0.94) bar (p=0.002) and 1.78 (SD 1.89) bar (p=0.752) at the same extension deformation. However, the rigid fixation increased the IDP of implant level and adjacent level of injured spinal column to 8.22 (SD 3.83) bar (p=0.506) and 13.41 (SD 9.77) bar (p=0.046) at the same flexion deformation. Compared to the rigid fixation system, the dynamic spinal stabilization at all constraint level did not affect the IDP during the extension motion. However, the stabilization system did reduce the IDP of adjacent level when the constraint was set from 20% to 90% looseness during the flexion motion.
Conclusions: This study proved the concept of tuning a dynamic spine stabilizer to be feasible. The degree of motion compensation of adjacent level is contradicted to the looseness of dynamic stabilizer. We found the optimal looseness to be from 40% to 80% for flexion and from 30% to 60% for extension. Otherwise, the dynamic stabilizer can both reduce the elevated IDP of implanted level due to injury during extension, and the elevated IDP of adjacent level due to rigid fixation during flexion.

中文摘要 i
ABSTRACT iii
目 錄 v
圖目錄 vii
表目錄 viii
第一章 前言 1
1.1脊椎基本架構 1
1.2後方脊椎融合術適用症狀 1
1.3後方脊椎融合術常見併發症及診斷方式 3
1.4後方脊椎融合術力學性質變化文獻回顧 4
1.5動態式脊椎固定系統的發展及臨床結果 5
1.6動態式脊椎固定系統力學性質變化文獻回顧 6
1.7 研究目的 6
第二章 材料與方法 7
2.1研究方法簡介 7
2.2實驗儀器 7
2.2.1混合式力學測試機台 7
2.2.2 微型針式壓力感測器 8
2.2.3 活動範圍限制裝置 9
2.2.4 X光機 11
2.3實驗流程 11
2.3.1試樣處理 11
2.3.2感測器置入 12
2.3.3力學測試 12
2.4資料分析 15
第三章 實驗結果 16
3.1相對活動角度 16
3.1.1 前彎動作 16
3.1.2 後仰動作 16
3.2椎間核壓力 16
3.2.1 前彎動作 16
3.2.2 後仰動作 17
第四章 綜合討論 23
第五章 結論與未來展望 26
參考文獻 27

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