The effect of implant constraint on results of conversion of unicompartmental knee arthroplasty to total knee arthroplasty.

A series of unicompartmental knee arthroplasty (UKA) revision to total knee arthroplasty (TKA) was compared to a group of primary TKAs performed at the same institution. The UKA revision group had a higher incidence of local wound complications and inferior clinical results as measured by Knee Society scores. When the revisions were stratified by the degree of interface constraint, knees revised with posterior cruciate ligament (PCL) substituting designs had superior knee scores that were comparable to the primary group. The use of a PCL-substituting knee design is recommended when converting a UKA to TKA.