Limited ability of coronal alignment parameters to assess rotational alignment in patients with varus knee osteoarthritis: a cross-sectional study

PURPOSE: This study aimed to investigate whether rotational alignment parameters vary across different severities of varus deformity and to examine the correlation between coronal and rotational alignment parameters in end-stage varus knee osteoarthritis (KOA). METHODS: We performed a retrospective study on 315 lower extremities with end-stage KOA. The lower extremities were categorized into the mild varus group (n = 141) and the severe varus (n = 174) group according to mechanical hip-knee-ankle angle (mHKA). Coronal alignment parameters were measured on standing full-limb radiographs, including the mHKA, lateral distal femoral angle (LDFA), and medial proximal tibial angle (MPTA). Rotational alignment parameters were measured on computed tomography (CT), including the femoral anteversion angle (FAA), condylar twist angle (CTA), and tibial torsion angle (TTA). RESULTS: We found no significant differences in any lower-limb rotational parameters between the mild varus and severe varus groups. Correlation analysis revealed that only TTA was significantly correlated with coronal alignment parameters, which was associated with MPTA in the mild varus group (r = 0.200, p = 0.020), mHKA in the severe varus group (r = 0.239, p = 0.001), and MPTA in the entire varus cohort (r = 0.118, p = 0.036). CONCLUSION: The assessment of lower limb coronal alignment has limited ability to evaluate rotational alignment in patients with end-stage varus knee osteoarthritis. Therefore, surgeons cannot rely on coronal alignment to estimate rotational parameters in patients with varus deformity, and CT examination is recommended for accurate assessment of rotational parameters.