Femorotibial rotational mismatch of the Oxford unicompartmental knee in the flexion position is a risk for poor outcomes.

Abstract

Femorotibial rotational mismatch has been reported to cause unsatisfactory outcomes after total knee arthroplasty. However, to our knowledge, no previous reports have described the relationship between the femorotibial rotational mismatch and clinical outcomes of Oxford unicompartmental knee arthroplasty (UKA). In total, we studied 52 knees with primary varus knee osteoarthritis that underwent Oxford UKA with a navigation system. Tibial component internal rotation angles relative to the femoral component at extension and flexion angle of 90° were measured using a navigation system. We evaluated the relationship between the clinical outcomes and femorotibial rotational mismatch angles. Additionally, we evaluated the relationships between the outcomes and rotational alignments of the femur and tibial components measured by computed tomography (CT). The tibial component internal rotational angle relative to the femoral component was significantly larger at a flexion angle of 90° than on extension (P < .001) and showed negative correlations with the Knee Society Functional Score and the pain and sports subscales of the Knee Injury and Osteoarthritis Outcome Score. Rotational alignment of the femur and tibial components on computed tomography was not associated with clinical outcomes. The tibial component internal rotational angle relative to the femoral component in the flexion position was negatively correlated with clinical outcome. Surgeons should pay attention to a rotational mismatch between components in the flexion position during the Oxford UKA procedure. Navigation systems will be effective in reducing the femorotibial rotational mismatch and improving clinical outcomes.