Can We Use the Posterior Condylar Off set as a Predictive Factor for Overhang of the Implant in Total Knee Arthroplasty?

PURPOSE We tried to demonstrate whether the posterior condylar offset (PCO, the distance from the femoral diaphysis posterior cortex to the posterior condylar margin) and ratio (PCOR, dividing PCO by the maximum antero-posterior diameter of the distal femur) could be used as predictive factors for overhang of the implants or using gender implants in total knee arthroplasty (TKA). MATERIALS AND METHODS One hundred and one women who underwent TKA using NexGen® (LPS) implants, were analyzed prospectively. After distal femoral resection, the mediolateral (ML) width was measured at four points (anterior, distal anterior, distal posterior and posterior) and compared with the ML width of the implant. The aspect ratio (AR, ML/AP ratio) and anterior/distal posterior ML width (Ant/DP) were calculated. Preoperative radiographic PCO and PCOR were measured. Differences of PCO, PCOR, AR and Ant/DP according to the size were analyzed and correlations between PCO, PCOR and AR were also analyzed. The patients were classified into two groups according to the presence of overhang, and differences of each parameter were compared between the two groups. RESULTS The size of the implant was positively correlated PCO, not significantly correlated with PCOR, and negatively correlated with AR and Ant/DP. PCO and PCOR and AR showed no correlation with each other. PCO and PCOR were not significantly different between the two groups. However, AR and Ant/DP were statistically low in the group with overhang. CONCLUSIONS Preoperative radiographic PCO or PCOR could not be used as a predictive factor for overhang of the implants or using gender implants in TKA.