Can preoperative lower limb alignment angles predict necessary soft tissue release during total knee arthroplasty for varus knees? A retrospective cohort study.

Purpose: A proper balance of soft tissues is essential in total knee arthroplasty (TKA) for varus knees, but assessing soft tissue tension preoperatively is challenging. This study aimed to determine whether lower limb alignment angles can predict the necessary degree of soft tissue release.

Methods: A retrospective cohort study was conducted on 953 patients with varus knees (> 10°) who underwent primary TKA from 2018 to 2020. The patients' data, release stage data, and three-joint alignment radiograph parameters were extracted from the Joint Reconstruction Research Center Knee registry, focusing on variables such as age, sex, body mass index (BMI), femoral mechanical‒anatomical angle (FMAA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), joint line congruent angle (JLCA), and varus angle (VA). Data analysis was performed via SPSS 26.0.

Results: The mean age of the patients was 65.4 (43-86) years, with a predominance of females (57.9%). Findings revealed significant associations between soft tissue release and FMAA, LDFA, MPTA, JLCA, MPTA/VA, and JLCA/VA. ROC curve analysis indicated that the JLCA/VA ratio had the highest predictive accuracy (0.997). A cutoff value of 0.49 for JLCA/VA was used to predict the soft tissue release grade, with a sensitivity of 98.8% and specificity of 99.9%.

Conclusion: Angular parameters from three-joint alignment radiographs can effectively predict soft tissue release needed for TKA in varus knees, with the JLCA/VA being the most reliable parameter.