Background: After total knee arthroplasty (TKA), the femur tends to be located posteriorly under weight-bearing (WB) conditions, and a paradoxical femoral anterior motion occurs, leading to joint instability.
Objective: We aimed to clarify factors which affect the postoperative femoral anteroposterior position relative to the tibia under WB conditions (A-P position) in medial pivot (MP) TKA.
Methods: Among 126 knees (81 women) with primary TKA using MP prosthesis for varus osteoarthritic knees, 70 knees had cruciate-retaining inserts (CR) with the reduced conformity and 56 knees had cruciate-substituting inserts (CS) with the full conformity. Using the three-dimensional (3D) assessment system, the associations between the A-P position and the factors including pre- and postoperative lower extremity alignment, component positions, and posterior femoral condylar offset (PCO), were assessed regarding the type of inserts.
Results: Significant correlations were seen between the A-P position and posterior tibial slope (PTS), medial PCO, and lateral PCO. Regarding the difference between the two inserts, the PTS, medial PCO, and lateral PCO significantly correlated with the A-P position in the CR, but only the PTS correlated in the CS.
Conclusions: The increased PTS and decreased PCO were the dominant factors for the A-P position in MP TKA.
Keywords: Femoral anteroposterior position; posterior condylar offset; posterior tibial slope; three-dimensional lower extremity alignment assessment system; total knee arthroplasty.