Abstract
Introduction
Postoperative knee flexion is an important indicator of success in total knee arthroplasty (TKA). Factors influencing the postoperative range of motion (ROM) were reported to be preoperative ROM, primary indication, height of postoperative joint line, patellar thickness, postoperative pain and rehabilitation. In this study, we aimed to identify the relationship between preoperative hip ROMs and postoperative knee flexion through reviewing the TKA results in Japanese patients.
Patients & Methods
We retrospectively reviewed primary TKAs 55 knees in 55 patients (33 left and 22 right) between April 2012 and March 2013 inclusive. The patients were 11 men and 44 women, with a mean age of 76.7 years. Preoperative hip ROMs and perioperative knee flexion were measured by using goniometer. Hip ROMs were flexion, extension, abduction, adduction, external rotation; ER, internal rotation; IR and total rotation; TR (The total rotation added up ER and IR.). Hip ROMs were measured passively, with the pelvis was fixed manually. Postoperative knee flexion was measured in the fourth week. The patients were classified according to the good group (28 knees), the postoperative knee flexion was more than 125 degrees; and the poor group (27 knees), less than 120 degrees. We compared preoperative hip ROMs in each groups. Multiple regression analysis and Single regression analysis were used for comparison between preoperative hip ROMs and postoperative knee flexion. For comparisons between paired groups we used Wilcoxon test, between unpaired groups Mann-Whitney U test. A p value of less than 0.05 was considered significant.
Results
Knee flexion of all patients did not have significant changes before and after the operation (p=0.09). Although the good group was a similar result (p=0.94), the poor group significantly decreased after the operation (p=0.01). (Table 1) The linear combination of hip ER and hip IR explained 28% (R2 = 0.28, p=0.0008) of the variance in postoperative knee flexion. The correlation coefficient of postoperative knee flexion and preoperative flexion was 0.41 (p=0.0017), and postoperative knee flexion and hip IR was 0.27(p=0.048), and postoperative knee flexion and hip TR was 0.35(p=0.008). There were only a low correlation between hip ROMs and postoperative knee flexion. (Table 2) As for the hip ER and hip IR, there were no significant differences between good group and poor group, however there was a significant difference for the hip TR between the two groups (p=0.013).(Figure 1)
Discussion
The mean postoperative flexion of our patients was 122.4°, with a loss of 2.4° flexion but postoperative flexion was improved on equality with preoperative flexion. There was a positive correlation between preoperative and postoperative flexion. This study also showed that there was a positive correlation between postoperative flexion and preoperative hip TR. A new finding is that there was a significant difference for the hip TR between good group and poor group. These finding may imply that biarticular muscles of origin around hip joint participate with the postoperative flexion. We conclude that it is important for TKAs to evaluate hip ROMs.
