拇指在大部分手部功能中扮演不可或缺的角色，日常生活中常見的手部行為都是拇指與其他四指互相配合完成，拇指的出色表現也在於它擁有腕掌關節可以提供手部執行對掌，而對掌在這些手部行為當中提供了很大的幫助。但是在此拇指腕掌關節卻常常被發現有退化的情形發生，相關的研究也指出在比較嚴重的退化情形下，患者會被建議以關節置換術來治療，在植體的選擇上有鞍狀關節，球窩關節等等人工關節，但在臨床上卻沒有明確的植體置換建議，因此本研究想藉由力學分析的方法，探討這兩種不同型態的拇指腕掌關節在拇指肌肉力學表現上的差異性，並可以提供力學資訊以供在置換人工關節時參考。
實驗方法是以Matlab建立數學模型並分析拇指在側向按壓時之肌肉力量分佈並且分成鞍狀拇指腕掌關節與球窩狀拇指腕掌關節兩組進行分析，側向按壓有三個按壓位置，在每個位置上有兩種按壓力量，模型需要的基礎資料是按壓時的拇指骨頭位置(遠端指骨，近端指骨，掌骨與斜方骨)、關節角度與按壓力量的大小，資料來源為受測者按壓荷重元件時所記錄的力量讀值並同時拍攝電腦斷層掃描影像，將資料匯入程式之後經過最佳化的運算可以得到兩個組別的肌肉力量與關節反力。
實驗結果顯示出在不同的按壓位置上，球窩狀關節型態，關節的軸向力皆明顯大於鞍狀關節，並且在肌肉力量上是以外展姆長肌最有顯著的變大，有相關研究指出在置換球窩狀人工關節時，植體常常會有陷入骨頭的情況發生，這狀況與軸向力的變大應有相當大的關係，總和來說，在置換球窩狀關節之後的肌肉受力會較原本的鞍狀關節大，而關節軸向力也會增加。

Many daily activities are completed by hands such as writing, typing, using phone, etc. In these motions, thumb opposition is an important component. And the CMC joint of thumb provides the ability to do the opposition motion. But degeneration is often observed in CMC joint. It was reported that 6% of men between 55 to 64 years old were observed to have CMC degeneration, and 25% of postmenopausal women were observed to have osteoarthritis (OA) in CMC joint. Arthroplasty is necessary when severe degeneration of CMC joint was observed. The saddle type and ball-and-socket type implants are often selected in arthroplasty. But few studies compared the advantage of different types of implants. Therefore the purpose of this study is to compare these two types of CMC joints by observing the tendon forces and joint constraints.
This study built up a model to simulate muscle forces of the thumb during pinching. This model was established by a customized program. The model was separated into two parts in which the CMC joints were saddle type and ball-and-socket type, respectively. There were three pinching positions, and there were two magnitudes of pinching force at each pinching position. The inputs were the relationship of bones (distal phalangeal, proximal phalangeal, metacarpal and trapezium) from CT image and pinching force measured from loadcell, and the outputs were tendon forces and joint constraints.
The results showed the axial loadings in the group of ball-and-socket type of CMC joint were significant higher than those in the group of saddle type of CMC joint. The tendon force in APL also showed significant increasing in the group (ball-and-socket type of CMC joint). There were studies indicating that subsidence was often observed in ball-and-socket type implant, thus, the increasing of axial loading may explain this situation. In conclusion, the axial loading and muscle forces in the group of ball-and-socket type of CMC joint were higher than those in the group of saddle type of CMC joint.

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