Fujii Tadashi, Matsui Yoshio, Noboru Marehoshi, Inagaki Yusuke, Kadoya Yoshinori, Tanaka Yasuhito
Department of Orthopaedic Surgery, Kashiba Asahigaoka Hospital, Kaminaka 839, Kashiba, Nara 639-0265, Japan.
Department of Orthopaedic Surgery, Osaka Rosai Hospital, Nagasone-cho 1179-3, Kita-ward, Sakai, Osaka 591-8025, Japan.
Case Rep Orthop. 2015;2015:217842. doi: 10.1155/2015/217842. Epub 2015 Jun 7.
We experienced two cases of atypical lateral dislocations of meniscal bearing in UKA (unicompartmental knee arthroplasty) without manifest symptoms. The dislocated bearing, which jumped onto the wall of tibial components, was found on radiographs in periodic medical examination although they could walk. Two thicker size bearing exchanges were promptly performed before metallosis and loosening of components. Continual examination is important to mobile bearing type of UKA because slight or less symptoms may disclose such unique dislocation. One case showed malrotation of the femoral component on 3D image. Anteroposterior view hardly disclosed the malrotation of the femoral component. Epicondylar view is an indispensable view of importance, and it can demonstrate the rotation of the femoral component. The the femoral distal end is wedge shaped and is wider posteriorly. If the femoral component is set according to the shape of medial condyle, the femoral component shifts to medial site compared with tibial component in flexion. It can account for such rare dislocation as follows. If excessive force applies on most medial side of the bearing during flexion, the lateral part of the bearing pops and the force squeezes it laterally simultaneously. Finally, the bearing jumps onto the lateral wall of the tibial component.
我们遇到两例在单髁膝关节置换术（UKA）中半月板假体发生非典型外侧脱位但无明显症状的病例。尽管患者仍能行走，但在定期体检的X线片上发现脱位的假体跳到了胫骨组件的壁上。在发生金属沉着病和组件松动之前，迅速进行了两次更大尺寸的假体置换。对于UKA的活动型假体，持续检查很重要，因为轻微或不太明显的症状可能会揭示这种独特的脱位情况。其中一例在三维图像上显示股骨组件旋转不良。前后位片很难显示股骨组件的旋转不良。髁上视图是一个不可或缺的重要视图，它可以显示股骨组件的旋转情况。股骨远端呈楔形，后部更宽。如果根据内侧髁的形状安装股骨组件，在屈膝时股骨组件相对于胫骨组件会向内侧移位。这可以解释如下这种罕见的脱位情况。如果在屈膝时对假体最内侧施加过大的力，假体的外侧部分会弹出，同时力会将其向外侧挤压。最后，假体跳到胫骨组件的外侧壁上。
