Posterior condylar offset and flexion in posterior cruciate-retaining and posterior stabilized TKA

Background. Anterior tibial translation associated with posterior impingement has been reported to be one of the factors limiting flexion after posterior cruciate-retaining (CR) total knee arthroplasty (TKA), especially when posterior condylar offset is decreased postoperatively. On the other hand, its effect on postoperative motion in posterior-stabilized (PS) TKA remains unknown. It has been demonstrated that PS TKA exhibits a consistent posterior femoral rollback during flexion. Thus, we hypothesized that the problem of posterior impingement can be avoided by use of PS TKA. In this study, we examined the relationship between postoperative posterior condylar offset and knee flexion in CR and PS TKAs. Methods. In this study, analysis was performed for 20 subjects who underwent bilateral TKAs (one CR and one PS TKA) as well as another group of 50 PS TKAs. All patients could be tracked for a minimum of 2 years. The range of flexion was measured before operation and at follow-up. Preoperative and postoperative posterior condylar offset was evaluated on true lateral radiographs. Results. At the follow-up examination, the mean flexion angle was 123 degrees in the CR knees and 131 degrees in the PS knees with a significantly greater improvement observed for the latter group. In the roentgenographic measurement of the posterior condylar offset, no significant difference was observed between the preoperative and postoperative values both in the CR and PS knees. We divided the patients into two groups according to the change of posterior condylar offset. The first group (Group I) showed a decrease in the posterior condylar offset after surgery and the second group (Group II) showed no change or an increase. Subsequently, postoperative change in flexion was compared between Groups I and II for the CR and PS knees. A significant difference between Groups I and II was observed in the CR knees, while no difference was observed in the PS knees. The magnitude of postoperative posterior condylar offset did not correlate with an improvement in maximum flexion angle in the 50 PS knees. Conclusions. It was shown that the magnitude of posterior condylar offset correlated with a postoperative change in flexion angle in CR knees, while no such correlation was observed in PS knees.