Quantitative evaluation of medial collateral ligament using sound touch elastography in patients with varus-type knee osteoarthritis

This study applied sound touch elastography (STE) to measure the shear wave velocity (SWV) of the medial collateral ligament (MCL) in patients with varus-type knee osteoarthritis (KOA), aiming to explore the clinical value of STE in the quantitative assessment of MCL stiffness. A total of 36 patients with varus-type KOA who underwent primary unilateral total knee arthroplasty (TKA) and required intraoperative MCL release were enrolled between May 2025 and May 2026. Meanwhile, 30 age- and sex-matched healthy volunteers were recruited as the control group. STE was performed to measure the mid-substance SWV of the MCL in all subjects. The intraclass correlation coefficient (ICC) was calculated to evaluate the intra- and inter-observer repeatability of STE-based MCL measurements. Independent samples t-test was used to compare MCL SWV values between the varus-type KOA group and the healthy volunteers. Receiver operating characteristic (ROC) curve analysis was conducted to assess the diagnostic efficacy of SWV for MCL contracture in varus-type KOA, and the optimal diagnostic cutoff value was determined according to the maximum Youden index. STE demonstrated moderate-to-good reliability for MCL stiffness measurement. The intra-observer ICC values for two sonographers were 0.80 and 0.85, respectively, and the inter-observer ICC was 0.79. Patients with varus-type KOA exhibited significantly higher MCL SWV than healthy volunteers (4.62 ± 0.86 m/s vs. 3.21 ± 0.49 m/s, P < 0.01). ROC curve analysis showed that the area under the curve (AUC) of SWV for diagnosing MCL contracture was 0.938 (95% CI: 0.886–0.991, P < 0.01). The optimal SWV cutoff value was 3.65 m/s, yielding a sensitivity of 94.4%, a specificity of 80.0%, and a Youden index of 0.74. Patients with varus-type KOA have significantly elevated MCL SWV compared with healthy individuals. STE allows stable, quantitative evaluation of MCL stiffness. Preoperative STE-derived SWV can provides a potential preoperative imaging reference for MCL stiffness evaluation.