Superior bearing dislocation in a unicompartmental total knee prosthesis.

The mobile bearing Oxford Unicompartmental Knee Prosthesis (OUKP) is the most commonly used treatment of osteoarthritis confined to 1 compartment of the knee. Dislocation of the mobile bearing is an uncommon but recognized complication of the OUKP. Patients typically present with severe pain and reduced range of motion of the affected knee. Radiological evaluation of OUKP can be challenging and requires knowledge of the prosthesis components and common complication patterns. Dislocation of the bearing can easily be overlooked on plain radiographs as the bearing is radiolucent, distinguished only by radiopaque markers. Further imaging in particular with CT may be required to adequately evaluate for prosthesis complications. Advances in prosthesis design and surgical technique may reduce the rate of bearing dislocation.