Influence of correction degree on the clinical effect of valgus knee after total knee replacement

Objective: To investigate the influence of correction degree on the clinical effect of valgus knee after total knee replacement(TKA). Methods: Clinical data of 91 patients with unilateral valgus knee who underwent TKA from January 2015 to December 2018 at Department of Orthopaedic Surgery,Zhongda Hospital,Southeast University were retrospectively analyzed. According to postoperative hip-knee-ankle angle(HKA),these patients were divided into neutral group (-3°≤HKA≤3°) and residual valgus group(HKA>3°). There were 70 patients in the neutral group,with a median age of 71.5 years(range:57 to 91 years),and 21 patients in the residual valgus group,with a median age of 71.5 years(range:60 to 85 years). The postoperative clinical indicators,including the range of motion (ROM),American Knee Society score(KSS),Western Ontario and McMaster University(WOMAC) osteoarthritis index,forgotten joint score (FJS-12) were collected. Meanwhile,the imaging indexes of femoral angle,tibial angle,femoral prosthesis flexion angle,tibial prosthesis posterior slope angle,patella tilt angle,congruence angle were also collected. Additionally,postoperative complications were recorded. The clinical data were analyzed by independent sample t test,Mann-Whitney U test or χ2 test. Results: There were no differences between the two groups in postoperative ROM (122.5°±8.5° vs. 119.4°±7.1°,t=1.534,P=0.128),KSS(159.8±8.9 vs. 150.0±8.9,t=-0.103,P=0.918),WOMAC osteoarthritis index(10.0(3.0) vs. 9.0(5.0),Z=-0.733,P=0.464),FJS-12(52.1(8.4) vs. 50.1(7.5),Z=-0.594,P=0.553)and femoral angle(94.0°(4.0°) vs. 94.0°(5.0°),Z=-0.209,P=0.835),tibial angle(90.0°(3.0°) vs. 91.0°(2.5°),Z=-1.226,P=0.220),femoral prosthesis flexion angle(3.0°(1.0°) vs. 3.0°(1.0°),Z=-0.652,P=0.514),tibial prosthesis posterior slope angle(4.0°(2.0°) vs. 4.0°(2.0°),Z=-0.763,P=0.445),patella tilt angle(9.0°(3.0°) vs. 9.0°(3.5°),Z=-1.429,P=0.153),congruence angle(14.0°(4.0°) vs. 15.0°(4.0°),Z=-1.690,P=0.091). However,abnormal proportions of patella tilt angle(33.3% vs.11.4%,χ²=5.630,P=0.018) and congruence angle(38.1% vs.17.1%,χ²=4.136,P=0.042) were apparent in the residual valgus group. The patients were follow-up for (32.1±5.2) months(range:24 to 40 months). Six weeks after operation,one case of joint stiffness occurred in the residual valgus group, which was improved after manual relaxation and rehabilitation exercises. At the last follow-up,two cases in the residual valgus group suffered patella instability which were fixed by patella braces and strengthening of the medial femoral muscles. There were no cases requiring reoperation for dislocation of patella,joint instability and aseptic loosening of the prosthesis in both groups. Conclusions: Residual valgus after TKA for valgus knee has no significant effect on the short-term clinical outcome,but it is more likely to cause abnormal proportions of patella tilt angle and congruence angle which may induce the risk of postoperative patella instability. The mid-and long-term outcomes need to be further investigated.