[Influence of posterior condylar offset and anteroposterior femorotibial translation on knee flexion after posterior cruciate-sacrificing self alignment bearing total knee arthroplasty].

OBJECTIVE: To observe the posterior condylar offset (PCO) changes and anteroposterior femorotibial translation, to investigate the influence of them on the maximum knee range of flexion (ROF) in patients with posterior cruciate-sacrificing self alignment bearing total knee arthroplasty (TKA).

METHODS: The clinical data were analyzed retrospectively from 40 patients (40 knees) undergoing primary unilateral TC-PLUS SB posterior cruciate-sacrificing self alignment and bearing TKA for osteoarthritis between January 2007 and June 2009. There were 18 males and 22 females with an average age of 70.6 years (range, 56-87 years). The disease duration was 5-14 years (mean, 9.1 years). The locations were the left side in 11 cases and the right side in 29 cases. Preoperative knee society score (KSS) and ROF were 48.0 +/- 5.5 and (77.9 +/- 9.0) degrees, respectively. The X-ray films were taken to measure PCO and anteroposterior femorotibial translation. Multiple regression analysis was performed based on both the anteroposterior femorotibial translation and PCO changes as the independent variable, and maximum knee flexion as the dependent variable.

RESULTS: All incisions healed by first intention. The patients were followed up 12-19 months (mean, 14.7 months). At last follow-up, there were significant differences in the KSS (91.9 +/- 3.7, t = -77.600, P = 0.000), the ROF [(102.0 +/- 9.3) degrees, t = -23.105, P = 0.000] when compared with preoperative values. Significant difference was observed in PCO (t = 3.565, P = 0.001) between before operation [(31.6 +/- 5.5) mm] and at last follow-up [(30.6 +/- 5.9) mm]. At last follow-up, the anteroposterior femorotibial translation was (-1.2 +/- 2.1) mm (95% CI: -1.9 mm to 0.6 mm); femoral roll forward occurred in 27 cases (67.5%), no roll in 1 case (2.5%), and femoral roll back in 12 cases (30.0%). By multiple regression analysis (Stepwise method), the regression equation was established (R = 0.785, R2 = 0.617, F = 61.128, P = 0.000). Anteroposterior femorotibial translation could be introduced into the equation (t = 7.818, P = 0.000), but PCO changes were removed from the equation (t = 1.471, P = 0.150). Regression equation was y = 25.587 + 2.349x.

CONCLUSION: Kinematics after TC-PLUS SB posterior cruciate-sacrificing self alignment bearing TKA with posterior cruciate ligament-sacrificing show mostly roll forward of the femur relative to the tibia, which have a negative effect on postoperative range of motion. There is no correlation between PCO changes and postoperative change in ROF in TC-PLUS SB posterior cruciate-sacrificing self alignment bearing TKA.