應用力控制與混合控制於前方腰椎椎間融合器與人工椎間盤之有限元素分析

Abstract

近年來，脊椎植入物的設計概念已經從傳統的提供患處穩定性(融合器)逐漸轉為恢復可動性(人工椎間盤)；冀望在手術後可以使患處恢復正常的生理運動行為，以避免鄰近端的軟組織加速退化病變。各式的測試方法也被提出來評估這些脊椎植入物的生物力學差異；其中以力控制與混合控制兩種施力方法比較受到生物力學學者的接受。然而，對於使用力控制或是混合控制來評估脊椎植入物可能導致的差異仍不明確。本研究希望透過有限元素分析搭配力控制以及混合控制兩種施力方法來評估前方腰椎椎間融合器與人工椎間盤在置入腰椎後對手術端以及鄰近端椎節影響。評估參數包含有運動範圍、小面關節接觸力以及手術鄰近端環帶的應力分布。 本研究透過Ansys 9.0有限元素分析軟體建構出一個三維的五節腰椎有限元素模型(INT)。依據臨床手術方式，將上述兩植入物放入腰椎第三與第四椎節之間，以分別建立出360度椎間融合模型(ALIF)以及椎間盤置換模型(ADR)。力控制的施加方式是施加150牛頓的預負荷以及10牛頓-米的彎曲力矩來模擬前彎、後彎、扭轉與側彎動作。而混合控制的施力方式則是施加150牛頓的預負荷，並參考標準測試法分別對前彎，後彎、扭轉與側彎動作施加約16.84度、14.73度、9.48度與17.14度的運動範圍。 就手術端而言，本研究建議兩種施力方式都可以用來預測ALIF模型的手術端穩定性；而力控制施力法會強調ADR模型的手術端影響。就鄰近端而言，混合控制施力法則會明顯指出ALIF模型對鄰近端的影響。若將目前研究結果與臨床發現相比較可以發現，力控制施力法比較有效的評估出椎間盤置換手術後手術端小面關節加速退化的病變；而混合控制則較有效的評估出椎間融合手術後鄰近端椎間盤與小面關節加速退化的病變。此外，相較於單純使用運動範圍來評估鄰近端椎間盤退化問題，使用應力分布的差異來評估鄰近端椎間盤退化病變是更好的方式，尤其是在評估人工椎間盤的影響時。 本研究認為兩種施力方法皆能被用來預測病患在日常生活的特別情形。混合控制法適合用來評估病患在術後的日常生活動作行為。而力控制法適合用來評估病患在術後的日常工作受力行為。

Recently, design concepts of spinal implants have changed from traditional stable fusion cages to mobile non-fusion artificial discs that attempt to restore normal physiological motion and lessen the deterioration of adjacent tissue. Several spinal testing protocols have been proposed to evaluate the biomechanical difference between these spinal implants, of which the load control method (LCM) and the new hybrid control method (HCM) are most popular worldwide. However, it is still not clear whether the LCM or the HCM should be preferentially used in evaluating the actual characteristics of spinal implants. This study used finite element (FE) analysis with the LCM and the HCM to analyze differences in range of motion (ROM), facet joint forces, and disc annulus stress at the implant and in adjacent levels after implantation of an anterior lumbar interbody fusion cage or an artificial disc. A 3-dimensional, five-level intact lumbar spine FE model was constructed using Ansys 9.0 software. At the L3-L4 level, the intact model was modified to construct surgery models, including an artificial disc replacement (ADR) with ProDisc II, and an anterior lumbar interbody fusion (ALIF) with cage plus pedicle screw fixation. The LCM imposed 10 N-m moments for each four physiological motions and a 150 N preload at the top of L1. The HCM process was otherwise in accordance with the standard hybrid testing protocol. The detailed ROMs are 16.84° in flexion, 14.73° in extension, 9.48° in torsion, and 17.14° in lateral bending, respectively. At the implant level, this study suggests that both control methods can be adopted to predict the behavior of a fusion model, and similar stabilization characteristics can be found with both methods. The LCM emphasized the effects of the non-fusion device at the implant level. At adjacent levels, the HCM emphasized the effects of the fusion device. By comparing present data with clinical findings, the LCM was found to be more effective and clinically relevant in evaluating the accelerative degeneration of facet joints at the implant level after the insertion of an artificial disc. The HCM was more effective and clinically relevant in evaluating accelerative degeneration of discs and facet joints at adjacent levels after the insertion of a spinal cage. In addition, this study demonstrates that the use of stress distribution patterns to predict adjacent disc degeneration produces better results than ROM, especially in cases of total disc replacement. This study suggests that these two analytical methods can be used to predict specific conditions in a patient’s daily life. The HCM is suitable for evaluation of the patient’s daily life motions during recovery and restoration of function after surgery. The LCM is suitable for evaluation of the patient’s normal lift work-loading conditions after surgery.