Nontraumatic, spontaneous dislocation of polyethylene tibial insert 1 year after TKA

The authors report a case of nontraumatic, spontaneous dislocation of a polyethylene insert detected 1 year after total knee arthroplasty. The patient demonstrated initial improvement and returned to work 4 months postoperatively. At 6 months postoperatively, the patient developed pain and a clunking sensation with motion; however, he denied any traumatic precipitating events. An arthroscopic procedure revealed arthrofibrotic formations but no signs of locking mechanism failure. At 12 months postoperatively, the patient developed sudden instability, and radiographs demonstrated an anteriorly dislodged insert. Revision surgery was performed, and the insert was removed. The insert showed some signs of fatigue due to the locking mechanism. We postulated that repetitive flexion produced an anterior superior force leading to failure of the locking mechanism.