Postoperative femoral anteroposterior position while standing correlates with the posterior tibial slope and posterior femoral condylar offset in medial pivot total knee arthroplasty

Abstract

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.