Introduction: Increasing popularity of unicompartmental knee arthroplasty (UKA) brings greater relevance for possibilities and outcome of revision surgery. UKA is less aggressive, allows earlier rehabilitation and better kinematics comparing to total knee arthroplasty (TKA). It is tempting to apply such advantages in cases with secondary degenerative changes in the opposite compartment after an UKA with satisfactory results by implanting a contralateral UKA (BiUni). Absence of loosening or wear with overcorrection under 5° after first prosthesis and patient selection criteria for UKA in the opposite compartment are required.

Material and Methods: From June 2004 to January 2007 six BiUni were done, out of ten secondary surgeries following UKA (six BiUni, three arthroscopies and one TKA conversion). Four consisted in external UKA after medial and two others the opposite. All have been submitted to prospective radiologic and clinical evaluation (International Knee Society Score-IKSS) with 25.5 months mean follow-up (12 to 42).

Results: Identified causes for secondary arthritic changes included: “hypercorrection” (n=3), partial lateral meniscectomy (n=2) and femoral condyle osteonecrosis (n=1). Before BiUni the mean IKSS knee was 62.5 (60 to 70) and IKSS function 65.0 (60 to 70). At latest revision, mean IKSS knee was 92.5 (80 to 100) and function 87.5 (70 to 100). No radiologic signs of wear or migration were noticed.

Discussion: There are only few papers in literature regarding this concept. BiUni is not about revising failed UKA neither is a bycondilar knee arthroplasty. These results encourage further evaluation about possible long-term advantages for strictly selected cases particularly those at higher risk for TKA.