MEDIAL-PIVOT TOTAL KNEE ARTHROPLASTY IS ASSOCIATED WITH LESS POSTOPERATIVE FEMOROTIBIAL ROTATIONAL BONE MISMATCH AND BETTER PATIENT-REPORTED OUTCOMES THAN POSTERIOR-STABILIZED TOTAL KNEE ARTHROPLASTY

Aims Excessive postoperative femorotibial rotational bone mismatch has been associated with inferior patient-reported outcome measures (PROMs) after total knee arthroplasty (TKA). Medial-pivot TKA (MP-TKA) may permit greater rotational accommodation between the femoral and tibial components, which may reduce the residual rotational mismatch between the femur and tibia. This study compared postoperative femorotibial rotational bone mismatch and PROMs between MP-TKA and posterior-stabilised TKA (PS-TKA). Methods Following 1:1 propensity score matching, 82 TKAs were analysed (41 MP-TKAs and 41 PS-TKAs). CT was performed two weeks postoperatively. Femorotibial rotational bone mismatch was measured using CT-based three-dimensional templating software and defined as the angle between a line perpendicular to the clinical epicondylar axis of the femur and Akagi's anteroposterior line of the tibia; positive values indicated external rotation of the tibia relative to the femur. PROMs were assessed at a mean follow-up of 51 months using the Knee Society Score 2011 (KSS-2011) and the Forgotten Joint Score-12 (FJS-12). Results Femorotibial rotational bone mismatch was significantly smaller in the MP-TKA group than in the PS-TKA group (−0.9° (SD 5.2°) vs 4.9° (SD 8.8°); p < 0.001). Conversely, intercomponent rotation was greater in the MP-TKA group than in the PS-TKA group (3.6° (SD 3.5°) vs −0.6° (SD 3.6°); p < 0.001). Excessive mismatch, defined as a value outside the range of −5° to 5°, was less frequent in the MP-TKA group than in the PS-TKA group (37% vs 61%; p = 0.046). The MP-TKA group had significantly higher KSS-2011 scores for symptoms, satisfaction, and functional activities, as well as higher FJS-12 scores (all p < 0.05). Excessive external femorotibial rotational bone mismatch (> 5°) was associated with lower KSS-2011 functional activity and FJS-12 scores. PS-TKA was independently associated with excessive femorotibial rotational bone mismatch (odds ratio 3.3, 95% confidence interval 1.2 to 8.8; p = 0.019). Conclusion MP-TKA was associated with less postoperative femorotibial rotational bone mismatch, greater intercomponent rotation, and higher scores in several PROM domains than PS-TKA. These findings suggest that greater intercomponent rotational accommodation may be associated with less residual mismatch between the femur and tibia and better patient-reported outcomes after TKA.