[Application of individualized setting of femoral opening point and valgus angle in artificial total knee arthroplasty for patients with external femoral arch].

OBJECTIVE

To investigate whether shifting the femoral opening point and setting a personalized femoral valgus angle can improve the lower limb force line of total knee arthroplasty (TKA) patients with external femoral arch.

METHODS

From March 2016 to October 2018, 50 patients (55 knees) with osteoarthritis with genu varus deformity combined with external femoral arch for TKA were selected. There were 10 males and 40 females. The age ranged from 63.1 to 80.5 years old, with an average of (67.8±5.8) years old. Forty-five cases were unilateral and 5 cases were bilateral. The osteoarthritis stages of 55 knees were Kellgren-Lawrence grade Ⅲ to Ⅳ; and the course of disease ranged from 2 to 10 years. PreoperativeSpecial Surgery (Hospital for Special Surgery) scores:pain was 15.20±3.52; function was 8.30±2.96;mobility was 10.15±2.85;muscle strength was 4.20±1.95;flexion deformity was 5.50±3.05;stability was 6.15±2.20; total score was 47.93±3.39. The external femoral arch angle ranged from 6.4° to 16.7°, with a mean of (10.63±2.29) °. The tibiofemoral angle ranged from 7.4° to 12.6°, with a mean of (12.04±3.59)°. The anatomical distal femoral angle ranged from 83.10° to 91.20°, with a mean of (84.55± 1.66)°. And the distance from the center of the knee joint to the lower limb line of force ranged from 2.01 to 6.00 cm, with a mean of (3.57±1.12) cm. During the replacement surgery, the femoral opening point and the valgus angle were individually set to obtain a good line of force of the lower limbs.

RESULTS

Before the operation, the distance of femoral opening point ranged from 0.24 to 0.74 cm, with a mean of (0.54±0.10) cm. The distance between the internal and external condyles of the femur ranged from 6.86 to 8.12 cm, with a mean of (7.27±0.27) cm. The preoperative valgus correction angle (VCA) ranged from 7.20° to 13.80°, with a mean of (9.38±1.38) °. The post-correction valgus correction angle' (VCA') ranged from 6.10° to 9.50°, with a mean of (7.36±0.82) °. All patients were followed up, and the duration ranged from 3 to 36 months, with an average of (13.5±5.8) months. All patients obtained good knee function after operation. Three months after operation, HSS scores included pain of 25.30±3.05, function of 18.25±2.05, mobility of 16.05±0.75, muscle strength of 6.20±2.10, flexion deformity of 8.80±1.85, stability of 8.20±1.75; and the total score ranged from 90.00 to 93.00, with an average of 91.82±0.98. The total score was higher than that before operation (=1.728, =0.038). Postoperative X-ray examination showed that there were no signs of loosening, sinking, or osteolysis of the prosthesis. The tibiofemoral angle on the weight-bearing X-ray on the second day after surgery ranged from 1.30° to 4.90°, with a mean of (2.53±0.83) °;the angle ranged from 87.50° to 91.30°, with a mean of (88.73±0.86) °;and the distance from the center of the knee joint to the lower limb line of force ranged from 0.02 cm to 1.20 cm, with a mean of (0.23±0.05) cm; which were improved compared with those before operation (=2.415, =0.019;=1.496, =0.041;=1.912, =0.033).

CONCLUSION

In TKA combined with external femoral arch, good lower limb force line and knee joint function can be obtained by externally shifting the femoral opening point and setting a personalized femoral valgus angle.