具關節牽引功能之上肢外固定器的設計與生物力學分析

Abstract

中文摘要 外固定器已被接受用來治療上肢關節如腕關節和肘關節的骨折。我們利用現有的商用外固定器來治療病患，並將治療的結果列述於本論文中。除了分析商用外固定器的功能與原理之外，我們也提出具有動態牽引功能的外固定器設計概念。 我們也針對所設計的外固定器做了生物力學分析。首先是骨針定位與肘關節角度對外固定器軸心對位的影響。從運動學觀點來看，骨頭與外固定器的架構形成了一個封閉的連桿系統。對於具備轉軸的動態外固定器，關節的動態牽引和軸心定位必定和設備(如外固定器的設計)，手術(如骨針定位)和關節的因素(如關節角度)相關。我們針對跨肘的外固定器連桿系統於不同初始條件做數值分析，得到不少組解可以達成軸心定位。這避免了單一解在手術上困難度極高的疑慮。 此外我們也評估了肘關節角度和骨針偏折對外固定器系統的同心牽引與牽引減少的影響，因為在臨床上知道關節表面被拉伸距離的減少是有助於手術的準備計劃。我們依據具轉軸的外固定器和強化的關節韌帶建立了四個有限元素分析模型。計算並比較了尺骨側與肱骨側因外固定器拉伸所引伸的距離及骨針沿特定力傳遞路徑固定於手肘上的影響，以改善具動態牽引功能的肘外固定器的使用情形。 最後我們利用齊次轉換矩陣進行運動學分析來評估骨針施打位置與插入角度對跨腕式關節外固定器的軸心對位之影響。分析骨針定位的改變於運動學上的限制。數值分析的結果同時用三角幾何模型與電腦模擬來驗證。各個骨針定位參數的影響並用田口氏工程方法加以驗證。經此齊次轉換矩陣分析所得的各種骨針位置與角度可作為外科醫師手術時的參考。同時適當的骨釘定位與最佳的外固定器設計所提供的軸心定位功能是術後跨腕關節運動的關鍵。

Abstract The external fixators have been used for the treatments of the fractures in the elbow joint and wrist joint of the upper extremity. The clinical practices using the commercial external fixators were performed and the positive results were reported in this thesis. Other than the commercial fixators of which we reviewed the function, we also proposed our conceptual design of the fixator with the arthrodiatasis. Several biomechanical analyses were performed based on the fixator of our design. Firstly we analysis the effect of the pin placement and the elbow angle on the hinge-alignment of the elbow fixator. From the kinematic viewpoint, the bone-fixator construct forms a closed linkage system. For the traditional static fixator, previous study demonstrated numerically that the placement of the fixing pins and the initial condition at the fracture site significantly restrained the fracture reduction and fixator adjustability. For the hinged dynamic fixator, the functions of joint distraction and hinge alignment might be closely related to some devices (e.g. fixator design), surgery (e.g. pin placement), and joint factors (e.g. elbow angle). In our parametric analysis of the bridged elbow-fixator linkage system under various initial configurations, there are multiple solutions to achieve hinge alignment which prevent the concerns that when only a unique solution exists for the hinge alignment, the arthrodiatasis inevitably becomes a highly technique-demanding surgery for setting the initial configuration of the bone-pin-fixator construct. Secondly we evaluated the effects of elbow angle and pin deflection on the concentric distraction and distraction loss of the elbow-fixator-pin construct since it is of clinical importance to clarify the loss between distracted distance of the articular surfaces and fixator’s distractor(s) for surgery planning. We deployed four finite-element elbow models with the unilaterally hinged fixator and stiffened periarticular tissues. The distraction values from the fixator distractor and fixing pins to the stiffened elbow, along the specified load-transferring path, were calculated and compared on both humeral and ulnar sides and thus improved the use of the elbow hinged fixator with arthrodiatasis. Thirdly we performed the kinemtic analysis to evaluate the influence of the pin locations and insertion angle to the hinge alignment of the bridging wrist joint fixator via the principle of homogeneous transformation matrix. The pin placement variables were parametrically changed to analyze their kinematic limitations. The numerical results were validated by the trigonometric model and computerized simulation. The influences of the pin placements were also evaluated with Taguchi method. The bone pin locations and orientations under different scenarios obtained from HTM analysis can be a good reference for the surgical application in the practical surgery. The current study demonstrated that the adequate pin placement and optimal fixator design which provided the hinge alignment function were critical for the postoperative bridged wrist motion.