Changes in femoral posterior condylar offset and knee flexion after PCL-substituting total knee arthroplasty: comparison of anterior and posterior referencing systems

Anterior referencing and posterior referencing are two major techniques for positioning femoral components and balancing the sagittal plane during total knee arthroplasty (TKA). The purpose of this study was to evaluate the changes in medial and lateral posterior condylar offset (PCO) after bilateral TKA using anterior referencing (AR) or posterior referencing (PR) systems and compare the effect of the PCO changes on knee flexion. Twenty female patients (mean age, 68.6 years) underwent bilateral TKA using the AR technique in one knee and the PR technique in the contralateral knee. Three-dimensional reconstructed computed tomographic images from the sagittal plane were used to evaluate PCO before and after arthroplasty. Knee Society scores and range of motion were evaluated postoperatively at a mean of 2.9 years. Postoperative medial and lateral PCOs were significantly greater (p < 0.001 and p = 0.048, respectively) in the AR group (30.9 +/- 2.2 and 29.1 +/- 1.5 mm, respectively) than those in the PR group (29.1 +/- 2.7 and 27.3 +/- 2.3 mm, respectively). In addition, the degree of change in the PCO after TKA was greater in the AR group than in the PR group. On the final follow-up, no differences in the degree of knee flexion were observed between the two groups (124.7A degrees for AR and 124.5A degrees for PR). Knee Society scores were similar in the two groups both preoperatively and postoperatively. On the final follow-up, individual changes in the medial and lateral PCO were not associated with changes in the knee flexion angle. Restoration of PCO after TKA was more accurate with the PR technique than with the AR technique. However, the postoperative differences in PCO showed no correlation with changes in knee flexion 2 years after PCL-substituting TKA. Therapeutic study, Level I.