Does a fixed distal femur resection angle influence radiographic alignment in total knee arthroplasty? / 中国组织工程研究

ABSTRACT

BACKGROUND: The distal femur resection in total knee arthroplasty is commonly made using a fixed angle relative to an intramedullary rod. Does a fixed distal femur resection angle influence radiographic alignment in primary total knee arthroplasty? OBJECTIVE: To research the femoral mechanical-anatomical angle in Chinese and how it affects the femoral component angle and postoperative mechanical alignment for total knee arthroplasty. METHODS: Totally 109 cases (148 knees) underwent primary total knee arthroplasty. One surgeon used a fixed resection angle of 5° (group A; n=56 cases, 76 knees). The second surgeon adjusted the resection angle according to preoperative coronal alignment, using 5° for neutral/mild varus, 6° for more severe varus, 4° for mild valgus and 3° for severe valgus knees (group B; n=53 cases, 72 knees). Preoperative hip-knee-ankle angle, femoral mechanical-anatomical angle, postoperative hip-knee-ankle angle, femoral component angle and tibial component angle were measured from standing hip-knee-ankle angle radiographs. For postoperative hip-knee-ankle angle, 177°-183° were considered as neutral mechanical axis. For femoral and tibial component angles, the target results were 88°-92°.RESULTS AND CONCLUSION: (1) There was no statistically significant difference between groups in postoperative hip-knee-ankle angle (group A (178.78±3.57)°, group B (178.23±2.78)°; P=0.302) and good rate of hip-knee-ankle angle (group A 62%, group B 65%). (2) The mean femoral mechanical-anatomical angle was (6.70±1.34)°preoperatively. There was no significant difference in the good rate of hip-knee-ankle angle (hip-knee-ankle angle < 7°69%; hip-knee-ankle angle ≥7° 55%; P=0.108) postoperatively. There was a statistically significant difference about good rate of femoral component angle between different femoral mechanical-anatomical angle angles (femoral mechanical-anatomical angle < 7° 76%; femoral mechanical-anatomical angle ≥7° 39%; P < 0.01). (3) There was a statistically significant correlation between preoperative femoral mechanical-anatomical angle and postoperative hip-knee-ankle angle (r=?0.42, P < 0.01) and postoperative femoral component angle (r=?0.58, P < 0.01). (4) The mean femoral mechanical-anatomical angle was larger than foreign values. When the resection angle less than femoral mechanical-anatomical angle, the femoral component may tend to be varus which could affect the lower extremity mechanical alignment. For the larger femoral mechanical-anatomical angle, we advise to adjust the resection angle according to measured value preoperatively.