Complications of Unicompartmental Knee Replacement

The most common complications of unicompartmental knee replacement are progression of osteoarthritis in the retained compartments, aseptic loosening and unexplained pain. A second opinion from an experienced UKR surgeon can be helpful in dealing with complex situations. It is important to obtain stress-views or Rosenberg views besides standard weight-bearing radiographs to identify osteoarthritis in the lateral compartment. The treatment options for symptomatic progression of OA in the retained compartments are revision to TKA or the addition of a lateral (or patellofemoral) UKR. Aseptic loosening is a frequent cause of failure in joint registries, but is uncommon in high volume centres, probably as consequence of the different interpretation of radiolucent lines. Infections are less frequent in UKR compared to TKR, however it should always be suspected in a painful UKR and investigated according to the current guidelines. Fracture is a rare but known complication of medial UKRs; risk factors such as technical errors, patient characteristics, and cementless UKRs can increase the incidence. Conservative treatment with restricted weight-bearing is usually effective for undisplaced or minimally displaced fractures. Bearing dislocation is an uncommon complication, specific for mobile-bearing designs. Bearing dislocations are usually characterised by acute pain and functional impairment, but can be silent. Unexplained pain is the second most common cause of revision of UKR and should be treated conservatively with active monitoring and reassurance. Adequate imaging should be performed to assess component positioning and rule out other possible causes of failure before considering revision surgery. Arthroscopy can be useful in cases of retained cement fragments or loose bodies or unexplained pain.