摘要
四聯桿義膝(4-bar linkage knee)是多心軸義膝(polycentric knee)的一種，它主要由兩組平行桿構成，兩組平行桿的不同排列位置，乃形成各式各樣的廠牌與型號；由於四聯桿義膝的瞬時旋轉中心(instant center of rotation)，是由兩組平行桿的延長線交集得來的，故不同廠牌與型號的四聯桿義膝，其瞬時旋轉中心各有特殊的軌跡。要分析四聯桿義膝，首先要知道當膝蓋伸直時，其瞬時旋轉中心的位置，在大轉子一膝一踝(T KA)連線的前或後（即阿爾法因子），以及在正常膝位置的上或下（即貝他因子）；其次要知道當膝蓋彎曲65或90度時，義肢大腿與小腿的長度和各縮短多少，此即L及S因子；最後還要知道當膝蓋彎曲90度，義肢大腿與小腿中心線的交點，離套筒內最低點多遠，此即K因子。當阿爾法因子是正值時，表示義膝的瞬時旋轉中心在大轉子-膝-踝連線的後方，負值則表在前方，故有正阿爾法值的義膝，其穩定度較高；當貝他因子是正值時，表示義膝的瞬時旋轉中心在正常膝位置的上方，負值則表在下方故有正貝他值的義膝，其義肢的槓桿力臂較長，患者較省力；當 L值越大，表示義膝彎曲65度時，整個義肢的長度縮短越多，因此在走路擺動期(swing phase)，無需刻意縮短義肢的長度，即有頗佳的趾尖離地(toe clearance)效果；S與K因子是在膝蓋彎曲90度時測得的，其值越大，則對去膝關節裁肢患者的美觀助益良多。
並列摘要
Four bar linkage knee is one kind of polycentric knees. It consists of two pairs of parallel bars. The instant center of rotation of 4-bar linkage knee is determined by the intersection of these two extended lines. It acts as an anatomical knee joint which is polycentric too. To analyze the 4-bar linkage knee, we should understand the following factors: alpha, beta, L, S and K. The alpha is determined by the distance between the instant center of rotation (ICR) and trochanter-knee-ankle (TKA) line. The alpha is positive if IRC is posterior to TKA, vice versa. The beta, is determined by the distance between the ICR and normal knee center, proximal as positive. Positive alpha and beta make prosthetic knee more stable and less energy consumption. L value represents the shortening effect of a four bar knee prosthesis during swing phase, while the S and K factors represent the advantages of a four bar knee in the sitting position, which are good for the long above-knee or knee disarticulation stumps. Four bar knee mechanism can provide the prosthetists with a selection of knee characteristics which were previously unavailable with a single axis knee.