This work aimed to evaluate the changes in the femoral posterior condylar offset (PCO) and tibial slope after posterior cruciate ligament (PCL)-substituting total knee arthroplasty (TKA), and to address the presence of any interactive effect between the two on knee flexion.
Fifty-two PCL-substituting TKAs were performed using a posterior referencing system. Three-dimensional reconstructed computed tomographic (CT) images were used to evaluate PCO and tibial slope before and after arthroplasty. Range of motion and clinical scores were evaluated at a mean of 3.1 years postoperatively. Multivariate linear model with interaction terms was used to evaluate and compare the relationships among changes in PCO, tibial slope, and postoperative knee flexion angles.
The degree of change in PCO was greater in the lateral condyle than in the medial condyle (3.1 ± 2.5 mm and −0.5 ± 2.8 mm, respectively). Postoperative medial and lateral tibial slopes were 1.4° ± 1.8 and 1.4° ± 2.0, respectively. The mean degree of postoperative knee flexion was 125°. Analysis with interaction terms and covariate adjustment demonstrated that medial PCO and tibial slope were significantly related to knee flexion with interactive effect (P = 0.011). In cases with <3° posterior tibial slope, the postoperative PCO was positively correlated to the degree of knee flexion angle. However, in cases with >3° tibial slope, PCO was negatively correlated to knee flexion.
Medial femoral PCO and tibial slope showed interactive effect on knee flexion after PCL-substituting TKAs. Reconstitution of the proper PCO and avoiding excessive tibial slope may be necessary.