| Objective To observe the posterior condylar offset (POC) changes and anteroposterior femorotibial translation, to investigate the influence of them on maximum knee range of flexion (ROF) in patients with posterior cruciatesacrificing self al ignment bearing total knee arthroplasty in order to provide certain theoretical guidances for the intraoperative installation of femoral prosthesis and prosthesis design. Methods The clinical data were analyzed retrospectively from 40 patients (40 knees) undergoing primary unilateral TC-PLUSTM SB posterior cruciate-sacrificing self al ignment and bearing total knee arthroplasty for osteoarthritis between January 2007 and June 2009.Forty patients with primary unilateral self alignment bearing total knee arthroplasty were selected. The criteria for inclusion were a preoperative diagnosis of end-stage osteoarthritis of the knee which had been operated by the same experienced orthopedist according to the same standard surgical procedure with TC-PLUS-SB type prosthesis. Postoperative rehabilitation programme were guided by the same rehabilitation therapist. All cases which preoperative range of motion not more than 90 degrees had been operated more than one year before our study and had a good or excellent postoperative result.The X-ray films showed prosthesis alignment was excellent.Patients were 56-87 years,averaged 70.6 years,and were composed of 18 knees of male and 22 knees of female(left,11;right,29). The duration of course was 5 to 14 years (average 9.1 years). Preoperative knee society score (KSS)and ROF were (48.0±5.5) points and (77.9±9.0)°, respectively. At last follow-up,the ranges of anteroposterior femorotibial translations and maximum knee flexions and postoperative posterior condylar offset changes were measured on lateral photograms with DICOM Explorer image analysis software. Test of normality was used objective variables. A paired t test was used for comparison beween preoperative and postoperative posterior condylar offset .Multiple regression analysis was performed during anteroposterior femorotibial translation and posterior condylar offset changes (Both were as the independent variable)and maximum knee flexion(It was as the dependent variable). Results Kolmogorov-Smirnov normality tests show that all measured data are normally distributed. The patients were followed up 12-19 months (mean 14.7 months). At last follow-up, There were statistically significant differences in the KSS (91.9±3.7) (t=—77.600, P=0.000), the maximum knee flexion (102.0°±9.3°) (t=—23.105, P=0.000) when compared with preoperative values. Significant difference was observed in POC (t= 3.565, P= 0.001) between before operation [(31.6±5.5 )mm] and at last follow-up [(30.6±5.9)]. At last follow-up, the femoral roll back was (—1.2±2.1)mm (95% CI:—.9 -—0.6); femoral roll forward was occurred in 27 cases (67.5%), no roll in 1 and femoral roll back in 12 cases (30.0%). By multiple regression analysis (ie Stepwise method), the regression equation was establ ished (R=0.785, R2= 0.617, F= 61.128, P=0.000). Anteroposterior femorotibial translation could be introducted into the equation (t=7.818, P=0.000), but posterior condylar offset changes were removed from the equation (t= 1.471, P= 0.150). Regression equation was Y=25.587 +2.349 X. Conclusion Majority of kinematic mode after TC-PLUS self alignment bearing total knee arthroplasty shown roll forward of the femur relative to the tibia, which had a negative effect on postoperative range of motion. If the femur to relative the tibia moved forward by 1mm, postoperative range of motion would reduce 2.35°.The causes for paradoxical roll forward that may be intraoperative sacrificing of posterior cruciate ligament or prosthesis designing remains to be studied. No statistical correlation beween posterior condylar offset changes and postoperative change in flexion angle was observed in self alignment bearing knees,which may be relative to a lesser toward or backward translation on the whole between the femoral and tibial prosthesis in knee joint flexion... |
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