Late Mobile-Bearing Dislocation in Unicompartmental Knee Arthroplasty

The authors present 2 cases of late mobile-bearing dislocation after unicompartmental knee arthroplasty with long-term follow-up. Patients had anterior bearing dislocation more than 10 years after primary unicompartmental knee arthroplasty. Retrieved mobile bearings showed severe erosion on the posterior lip, suggesting frequent deep knee flexion as the cause of wear. Bearing dislocation is known to occur in the early postoperative phase. However, for Asians with a lifestyle that requires high knee flexion, dislocation might occur in the late postoperative phase. Such late bearing dislocation has a mechanism different from those reported in previous studies. Loss of bump in the posterior lip was found to be the cause. After late bearing dislocation, conversion to total knee arthroplasty is unnecessary because a simple bearing exchange will suffice. [ Orthopedics . 2019; 42(1):e124–e127.]