動態式脊椎固定器之測試方法設計

Abstract

中文摘要 背景：動態穩定系統是近年來改善脊椎融合術併發症的有效方法之一，為了測試動態穩定系統的有效性，有必要建立一套測試系統。 目的：以混成測試法為基礎，建立一可執行扭矩控制與角度位移控制的連續式彎矩測試機台，接著以混成測試法，測試新型的動態穩定系統（Prototype of Dynamic Stabilizer，PDS）效能，並探討桿件的剛性與長度，對PDS系統效能的影響。 材料與方法：混成法測試機台，可測試單節或多節脊椎運動單元。機台利用馬達作動力輸出，藉由伸縮導桿組和上夾具傳達扭矩予試樣產生連續式純彎矩負載；LabVIEW程式即時監控扭力計與角度計訊號，控制馬達動力輸出方向、停止；CCD連續拍攝旗標上反光點的移動，藉由直接線性轉換法求得椎骨運動角度。機台完成後，選用一副人的腰椎(L1-L4)，先施予 8Nm的純彎矩，量測該試樣的總活動度(tROM_intact)及各節椎骨活動度(iROM_intact)。接著在L2-3節依序進行椎間盤傷害，植入Dynesys與PDS等裝置，然後對試樣施予純彎矩，直到試樣彎曲至與未受處置前的總活動度(tROM_intact)為止，紀錄此時各節椎骨活動度(iROM_construct)。替換PDS系統的桿件材質以及長度，重複測試步驟。 結果：CCD量測的精度為(±0.12°)；系統中扭力與角度位移控制精度為(±0.1Nm、±0.2°)。腰椎(L1-L4)在前彎後仰的總活動度為28.9°。L2-3椎間盤受損並裝上Dynesys後，L2-3及L1-2 (上鄰近椎節)活動度減少(51.1%，42.5%)，L3-4 (下鄰近椎節)活動度增加(42.3%)。若改換PDS系統，各椎節活動度的增、減趨勢與Dynesys相同，分別為L2-3減少(21.5%)，L1-2減少(55.7%)，L3-4增加(22.8%)。短桿件對不穩定椎節的固定效果比長桿件好，但會增加上鄰近椎節的活動度。 結論：本實驗成功架構一混成測試機台，能有效探討脊椎運動元在不同手術處置後，各椎節的活動度變化。本實驗發現：（1）Dynesys雖比PDS系統較更能重建不穩定椎節的穩定度，但卻會提高下鄰近椎節提早退化的風險；（2）PDS系統的效能可藉由提高桿件的剛性、降低桿件的長度來改善。 【關鍵詞】腰椎、混成法、動態穩定系統、生物力學、剛性、椎弓螺絲

ABSTRACT Objective. To establish a hybrid testing apparatus that provides “moment-control mode” and “angular-displacement-control mode”. The effect of the rod stiffness and that of the rod length on a prototype of dynamic stabilizer (PDS) were investigated using the current testing apparatus. Summary of Background Data. Dynamic spine stabilizer is a newly developed method to diminish the prevalence of early degeneration in adjacent levels. To estimate the effect of dynamic spine stabilizer, it is necessary to establish a testing apparatus. Methods. Using the established testing apparatus, a prototype of dynamic spine stabilizer（PDS）was tested on a cadaver lumbar spine (L1-L4). Following the hybrid testing protocol, the specimen was applied with a sagittle bending moment of 8Nm to obtain the range of motion (ROM) of the whole specimen (tROM_intact) and the ROM of each individual level (iROM_intact) included in the whole specimen. The L2-3 intervertebral disc was damaged at the outer anular fibrosus using a scapal, and then implanted with Dynesys and the PDS. The specimen was sagittaly bended to the ROM which was obtained with the application of 8Nm in the first place. The ROM of each individual level (iROM_construct) was measured simultaneously. The hybrid testing protocol was repeated while the PDS was replaced with other rods of with different stiffness and different length. Results. The angular measured precision of the current apparatus is ±0.12°.The precision of system in“moment-control mode”and“angular-displacement-control mode”is 0.5Nm and 0.2° .Dynesys restored the stability of the injuried L2-3 by 51.1%. The ROM of L1-2 (upper adjacent level) decreased by 42.5% and the ROM of L3-4 (lower adjacent level) was increased by 42.3%. The change of ROM of each individual level after implantation of PDS was in the similar pattern to that of Dynesys, with L2-3 decreased 21.5%，L1-2 decreased 55.7%，and L3-4 increased 22.8%. The stability of the L2-3 was increased with higher rod stiffness and shorter rod length.

Conclusion. A hybrid testing apparatus that is able to perform hybrid testing protocol is successfully developed. Using the established testing apparatus, the present study reveals that 1) Dynesys reduced more ROM of damaged level than the PDS does, but increased the risk of early degeneration in the lower adjacent level; 2) the efficiency of the PDS can be improved by the rod with higher stiffness and shorter length. 【Keywords】hybrid testing protocol、Dynesys, dynamic spine stabilizer