Knee medial tightness after total knee arthroplasty is associated with superior clinical outcomes in Chinese patients: a retrospective cohort study

In total knee arthroplasty (TKA), the relationship between joint gap and postoperative prognosis remains unclear. This study aimed to evaluate the impact of the postoperative medial-lateral joint gap difference on clinical outcomes following TKA in Chinese patients with preoperative varus deformity.

In this retrospective cohort study of 252 knees, patients undergoing primary posterior-stabilized (PS) TKA were grouped by postoperative medial-lateral gap difference. Clinical scores were assessed using KSS, WOMAC and FJS-12 at 1.70 ± 0.42 years of follow-up. Multiple comparisons among groups were performed using appropriate post hoc tests (Tukey or Dunn). Multivariable linear regression was performed to adjust covariates including age, preoperative hip-knee-ankle (HKA) angle gender and body mass index (BMI). Subgroup analyses were conducted to assess the consistency of the association across age, varus severity and BMI. Finite element analysis (FEA) was performed to compare biomechanical responses among healthy, postoperative balanced and postoperative medially tight model (simplified by reducing the medial insert thickness by 1.25 mm).

Both the medially tight and balanced groups achieved superior outcomes compared with the laterally tight group. Moreover, patients with a gap difference of 1.0–1.5 mm (medially tight) demonstrated greater improvements in total and functional scores than the balanced group. In subgroup analyses, medial tightness was associated with significantly greater improvements in patients aged > 70 years (p < 0.05) and this association were not altered after adjustment for other covariates. No significant differences were observed between the medially tight group and the balanced group in the other subgroups. The medially tight model exhibits a mechanical response that more closely resembles that of healthy individuals than does the balanced model.

For Chinese patients undergoing PS TKA, postoperative medial tightness is associated with better short-term functional recovery. Finite element analysis offers supporting evidence for the clinical findings.