股骨后髁偏心距在全膝关节置换术中的意义

Significance of posterior condyle offset in total knee arthroplasty

股骨后髁偏心距(PCO)这一概念由Bellmans于2002年率先提出,最早被认为与全膝关节置换术(TKA)后膝关节屈曲度相关。目前,PCO的测量方法主要包括4种:X线测量法简便易行,但因其忽略了股骨内外侧髁的不对称性,在原理上存在一定缺陷;CT、MRI法不受投照角度限制,但假体金属伪影的干扰不可忽略;影像学结合术中软骨厚度测量最为精确,但操作复杂并且主观性较强。PCO在TKA术中有着重要的临床意义:对于后交叉韧带保留型TKA,PCO通过影响股骨与胫骨撞击的旋转半径,使得膝关节最大屈曲度与之正相关。而在后交叉韧带替代型TKA中却没有这种关系,这可能与膝关节后方软组织的阻挡作用以及膝关节前方伸膝装置的限制作用有关。此外,PCO的改变会影响屈曲间隙,从而影响膝关节稳定性特别是屈曲位和半屈位的稳定性。这种改变同样会影响膝关节的解剖学结构及生物力学结构,进而有可能导致骨溶解及假体松动。过大的PCO会增加后方关节囊的紧张程度,造成伸直间隙的减小,带来膝关节屈曲挛缩的风险。因此在TKA术中,临床工作者有必要尽可能将PCO恢复到术前状态,以最大限度避免相应不良后果的发生。本文就PCO在TKA术中的临床意义作以综述。

Posterior condyle offset (PCO), firstly proposed by Bellmans in 2002, was thought to be associated with knee flexion after total knee arthroplasty (TKA) in the beginning. At present, four mainly methods have been widely used for measuring the PCO. X-ray is a simple and easy way, except for ignoring the asymmetry between medial and lateral femoral condyles, which leads to defects in principle. CT and MRI are not restricted by the projection angle, but the interferences of prosthetic metal artifacts cannot be ignored. Full-thickness cartilage-based posterior femoral condylar offset is the most accurate method, but the measurement is complicated and subjective. PCO has important clinical significance in TKA surgery. As for posterior cruciate ligament-retained TKA, the PCO affects the maximum knee flexion function by changing the radius of the rotation between femur and tibia. However, it doesn't happen in the posterior cruciate ligament replacement TKA, which may be related to the blocking of the soft tissue behind the knee and the restriction of the knee extension device. In addition, changes in PCO affect the flexion gap, which influences the stability of the knee joint, especially for flexion and mid-flexion. It also affects the anatomical structure and biomechanical structure of the knee joint, which may lead to osteolysis and early loosening. Excessive PCO increases the tension of the posterior joint capsule, resulting in a reduction of the extension gap, which brings the risk of knee flexion contracture. Therefore, it is necessary for physicians to restore the PCO to the preoperative state, in case of the occurrence of adverse consequences. This article summarized the clinical significance in TKA.