Patients with knee osteoarthritis exhibit an abnormal three-dimensional lower limb phenotype: An EOS imaging study

To characterize the weight-bearing three-dimensional (3D) lower-limb phenotype associated with knee osteoarthritis (KOA) and assess whether noncoronal measurements provide information beyond conventional coronal alignment. This retrospective cohort study used weight-bearing EOS images from a single-center database. Participants were classified by clinical diagnosis and radiographic assessment. Exact sex matching plus 1:1 nearest-neighbor propensity score matching for age and BMI (logit-scale caliper=0.10) generated 279 KOA-control pairs (n=558). Seventeen pelvic and lower-limb 3D parameters were quantified. Between-group differences were estimated using linear regression with matched-pair clustered robust standard errors and false discovery rate adjustment. After FDR adjustment, 9 out of 17 parameters differed. Compared with controls, patients with KOA had greater varus alignment (HKA β=-3.72°; 95% CI, -4.50 to -2.94), increased LDFA and HKS, decreased MPTA, greater femoral offset and neck length, and a reduced neck-shaft angle. KOA also revealed greater sagittal flexion (β=6.74°; 95% CI, 5.58-7.90) and internal femorotibial rotation (β=-2.95°; 95% CI, -4.43 to -1.47). In exploratory models, adding sagittal parameters to a demographic/coronal model increased the optimism-corrected AUC from 0.691 to 0.776. Together, these findings reveal a focused multiplanar, weight-bearing lower-limb phenotype in KOA patients, indicating that clinical and research phenotyping should move beyond coronal alignment alone and provide a structural framework for future biomechanical and longitudinal studies.