ROLLBACK IN POSTERIOR CRUCIATE LIGAMENT-RETAINING TOTAL KNEE ARTHROPLASTY - A RADIOGRAPHIC ANALYSIS

A clinical and radiographic study of 49 posterior cruciate ligament-re taining total knee arthroplasties in 38 patients (11 bilateral, 27 uni lateral), using prostheses of the same design, was undertaken to quant ify the amount of in viva rollback (ie, the anteroposterior translatio n of the tibia with respect to the femur during flexion). The mean dif ference in the distances between the contact points of the knees in fu ll 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 +7. 6 mm; SD, 4.7 mm) relative to the prosthetic tibial tray, correspondin g 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 itse lf, corresponding to an average translation of 0% of the true tibial s urface depth. The differences between the rollback values obtained fro m the 90 degrees and full-extension radiographs relative to the prosth etic tibial tray (P =.63) and the true tibia (P = .89) were not statis tically significant. Intraobserver (P =.27-.50) and interobserver (P = .13-.72) reliability tests showed that the differences between radiogr aphic measurements taken by the same observer at two different points in time and by two different observers were not statistically signific ant. No correlations were found between the degree of translation of t he tibiofemoral contact point relative to the prosthetic tibial tray a nd the posterior tilt of the tibial tray (R-2 =.12), the preoperative tibiofemoral angle (R-2 =.34), and the postoperative tibiofemoral angl e (R-2 = .027). No correlations were found between the degree of trans lation of the tibiofemoral contact point relative to the true tibia an d the posterior tilt of the tibial tray (R-2 =.16), the preoperative t ibiofemoral angle (R-2 =.14), and the postoperative tibiofemoral angle (R-2 =.034). In conclusion, this study indicated no demonstrable roll back occurring in the posterior cruciate ligament-retaining total knee arthroplasty used in this study.