Residual varus alignment after posterior-stabilized total knee arthroplasty limits medial soft tissue remodeling

Background: Proper lower limb alignment and soft tissue balance are significant indicators to measure the success of total knee arthroplasty (TKA). Previous studies have confirmed that soft tissue relaxation around the knee after TKA will change over time; however, the relationship between lower limb alignment and soft tissue balance after TKA is still unclear. We studied (1) whether the change of soft tissue balance around the knee with time after PS TKA would affect the alignment of the lower limbs; (2) Whether the accuracy of lower limb alignment during PS TKA affects postoperative soft tissue remodeling. Methods: In this study, 100 patients were recruited after PS TKA. Among them, 50 patients with a hip knee ankle (HKA) angle of ≤ ± 3 ° were set as the neutral group, and 50 patients with HKA angle of ＞± 3 ° were set as the deviation group. The imaging results measured the hip knee ankle (HKA) angle before the operation as well as the HKA, varus, and valgus angles at 1, 3, 6, 12, and 24 months after TKA. Clinical assessment included range of motion (ROM), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Knee Society Score (KSS). Results: Eight people were excluded in the experiment. The study enrolled 47 patients in the neutral group and 45 patients in the deviant group follow up for 2 years . During the follow-up, the HKA angles were 1.64 °, 1.66 °, 1.69 °, 1.67 °, and 1.64 ° in the neutral group and 4.35 °, 4.38 °, 4.40 °, 4.42 °, and 4.42 ° in the deviation group. There was no statistical significance in the changes of HKA angle in the follow-up of the two groups (P > 0.05). The mean varus angles of the patients in the neutral group were 5.77 °, 4.17 °, 4.06 °, 4.06 °, and 4.09 °, while the mean varus angles of the patients in the deviation group were 5.68 °, 4.20 °, 4.18 °, 4.09 ° and 4.05 °, with no significant difference between the groups (P > 0.05). The mean valgus angles of the patients in the neutral group and deviation group were 2.47 ° and 2.45 ° (P = 0.841), 3.45 ° and 2.88 ° (P < 0.001), 3.63 ° and 3.07 ° (P < 0.001), 3.60 ° and 3.06 ° (P < 0.001), 3.63 ° and 3.10 ° (P < 0.001). ROM, WOMAC and KSS of the two groups were significantly improved after operation, and there was no difference between the two groups. Conclusion: This study shows that whether the alignment is accurate or not in the early stage after TKA, the relaxation of the medial and lateral soft tissues of the knee joint change; however, this change will not significantly affect the alignment of the lower limbs. Postoperative residual varus deformity will limit medial soft tissue remodeling. Level of evidence III.