Objective: To analyze the effect of the distal femoral flexion angle (DFFA) on the sagittal alignment of femoral prosthesis and function recovery after total knee arthroplasty (TKA).
Methods: Between January 2007 and January 2009, 35 patients (35 knees) whose distal femoral flexion angle (DFFA) was more than 6 degrees underwent TKA. Reference to the method by Oswald for DFFA measurement, 35 patients were divided into 2 groups: group A (n = 23, 6 degrees < DFFA < 12 degrees, long intramedullary rod system) and group B (n = 12, DFFA > 12 degrees, short intramedullary rod system). Another random 30 osteoarthritis and 10 rheumatoid arthritis patients were selected as control group (group C, DFFA < 6 degrees). The postoperative femoral prosthesis flexion angle (FPFA), knee society score (KSS), the femoral notch, and extension dysfunction were analyzed.
Results: All incisions healed by first intention. Seventy-five patients were followed up 1-3 years (mean, 2.1 years). The X-ray films showed that no signs of loosening, fracture, or infection were observed. There were significant differences in FPFA, the femoral notch, and knee extension dysfunction at 1 year after TKA between 3 groups (P < 0.05). The knee extension angle of group B was significantly larger than that of groups A and C (P < 0.05). There was no significant difference in the knee flexion angle and KSS score between 3 groups (P > 0.05). KSS score of postoperation was increased significantly when compared with preoperative values in 3 groups (P < 0.05).
Conclusion: Long intramedullary rod system in patients with higher DFFA usually leads to anterior femoral notch in TKA, so short intramedullary rods that can effectively avoid the notch should be selected in patients with DFFA > 12 degrees. But when the femoral prosthesis would be in flexion position, extension dysfunction usually occurs.