Regional Differences in Knee Osteoporosis Based on Coronal Alignment Phenotype in Patients Undergoing Preoperative CT...

Background: Regional periarticular bone mineral density may influence fixation and survivorship in total knee arthroplasty, but its relationship to coronal alignment remains unclear. This study assessed the association between coronal knee alignment and osteoporosis using CT Hounsfield Unit (HU)-based thresholds. Methods: Patients aged ≥ 50 years with standing long-leg radiographs and phantomless knee-CT (2008-2025) were retrospectively identified. Exclusion criteria included >12 months between studies, incomplete CT, non-120 kV acquisition, prior fracture or surgery, or metabolic bone disease other than osteopenia or osteoporosis. Mean trabecular attenuation was measured over 15 mm of epiphyseal bone in the distal femur and proximal tibia. Osteoporosis was defined using CT-HU thresholds. Coronal alignment was measured using hip-knee-ankle angle (HKAA) and categorized as varus (<178°), neutral (178-182°), or valgus (>182°). Measurements were performed by a reviewer blinded to osteoporosis classification. Multivariable logistic regression adjusted for age, sex, body mass index, and Kellgren-Lawrence grade. Results: Among 306 patients (mean age 66.9 ± 9.0 years; 51.3% female), 99.3% underwent CT for arthroplasty planning. Osteoporosis prevalence was 34.3% of varus, 58.2% of neutral, and 68.6% of valgus knees. Increasing valgus alignment was associated with higher osteoporosis odds, whereas varus alignment showed lower odds. Female sex (OR 3.06; p < 0.001), age (OR 1.06/year; p < 0.001), and HKAA (OR 1.05/degree; p = 0.042) remained independently associated with osteoporosis, whereas Kellgren-Lawrence grade was nonsignificant. Conclusions: Coronal alignment was associated with CT-defined regional knee osteoporosis. Valgus alignment showed increased odds of osteoporosis, whereas varus alignment showed lower prevalence.