Objective: To reveal the characteristics of anatomical and mechanical axes in lower extremities by analyzing full length weight bearing X ray radiographsin patients with knee osteoarthritis(OA).
Methods: From June 2015 to May 2016, the lower extremity CTA was performed for 20 patients with vascular diseases, and these patients without OA were assigned to the normal group. There were 7 males and 13 females, ranging in age from 24 to 72 years old with an average age of 63.2 years old. The weight bearing full length X ray radiographs of the lower extremities were taken for 53 patients with knee OA, and these patients were assigned to the OA group. There were 10 males and 43 females, ranging in age from 52 to 80 years old with an average age of 64.7 years old. The osteoarthritis group were divided into two groups:varus knee group and valgus knee group. The femoral shaft double condyle angle(F), tibial shaft plateau angle(T), joint gap angle(JS), femoral tibial angle(FT), hip knee ankle angle(HKA), knee physiological valgus angle(KPV), and femoral offset were measured. The SPSS 21.0 was used to analyze the statistical data.
Results: The mean F were (79.9±2.3)° and (81.4±3.5)°, T were (93.8±3.7)° and (94.6±2.7)°, JS were (1.7±1.0)° and (2.1±2.5)°, FT were (175.4±4.0)° and (178.1±6.3)°, HKA were (181.4±4.1)° and (184.3±6.9)°, KPV were (6.0±1.0)° and (6.2±1.5)°, offset were (38.5±6.5) mm and (38.1±9.2) mm in the normal and OA group respectively. There was a significant difference in the KPV between varus knee and valgus knee groups(t=2.956, P=0.005), and the greater mean KPV was found in varus knee. Positive correlations were found between KPV and age(r=0.241, P=0.016), as well as between KPV and offset (r=0.946, P=0.000).
Conclusions: The average KPV in patients with knee OA was 6.2° in the present study, and the KPVs were also positively correlated with the patients' ages and the femoral offsets. The average KPV in the varus knee was greater than that of the valgus knee, and the difference was about 1°. The changes of mechanical parameters of lower limb may be one of the risks for developing knee OA. Analyzing the full length weight bearing X ray radiographs of the lower extremities preoperatively will be helpful to determine a individualized osteotomy method for patients.
Keywords: Arthroplasty, replacement, knee; Genu valgum; Osteoarthritis, knee; Radiometry.