Rollback in posterior cruciate ligament-retaining total knee arthroplasty. A radiographic analysis.

A clinical and radiographic study of 49 posterior cruciate ligament-retaining total knee arthroplasties in 38 patients (11 bilateral, 27 unilateral), using prostheses of the same design, was undertaken to quantify the amount of in vivo rollback (ie, the anteroposterior translation of the tibia with respect to the femur during flexion). The mean difference in the distances between the contact points of the knees in full extension and in 90 degrees flexion (ie, the rollback distance) was a posterior translation of the contact point of -0.2 mm (-12.7 to +7l6 mm; SD, 4.7 mm) relative to the prosthetic tibial tray, corresponding to an average translation of 0% of the prosthetic tibial tray depth, and -0.2 mm (-12.5 to +9.1 mm; SD, 4.8 mm) relative to the tibia itself, corresponding to an average translation of 0% of the true tibial surface depth. The differences between the rollback values obtained from the 90 degrees and full-extension radiographs relative to the prosthetic tibial tray (P = .63) and the true tibia (P = .89) were not statistically significant. Intraobserver (P = .27-.50) and interobserver (P = .13-.72) reliability tests showed that the differences between radiographic measurements taken by the same observer at two different points in time and by two different observers were not statistically significant. No correlations were found between the degree of translation of the tibiofemoral contact point relative to the prosthetic tibial tray and the posterior tilt of the tibial tray (R2 = .12), the preoperative tibiofemoral angle (R2 = .34), and the postoperative tibiofemoral angle (R2 = .027). No correlations were found between the degree of translation of the tibiofemoral contact point relative to the true tibia and the posterior tilt of the tibial tray (R2 = .16), the preoperative tibiofemoral angle (R2 = .14), and the postoperative tibiofemoral angle (R2 = .034). In conclusion, this study indicated no demonstrable rollback occurring in the posterior cruciate ligament-retaining total knee arthroplasty used in this study.