Native femoral geometry reveals consistent distal and posterior offsets with variable anterior compartment: a morphometric analysis

Abstract The three-dimensional geometric relationship between femoral condylar offsets has not been fully characterized. Current off-the-shelf (OTS) designs rely on linear scaling, assuming a fixed proportional relationship between compartments. The purpose of this study was to quantify condylar offset dimensions in a young non-osteoarthritic population and to determine whether a consistent geometric relationship exists between the anterior, distal, and posterior femoral compartments. Computed tomography (CT) scans of 265 prospectively collected knees (151 patients) were retrospectively analyzed. Anterior central offset (ACO), anterior lateral offset (ALO), anterior medial offset (AMO), distal medial offset (DMO), distal lateral offset (DLO), posterior medial offset (PMO), and posterior lateral offset (PLO) were measured relative to the surgical transepicondylar axis (sTEA) and normalized to epicondylar width. Pairwise differences, inter-compartmental ratios, and Pearson correlation coefficients were computed to determine a possible morphologic link between offsets. Following normalization, no significant sex difference was detected across any offset parameter (all p ≥ 0.198). Distal and posterior offset ratios approached unity in both compartments (PMO/DMO: 0.99 ± 0.06; PLO/DLO: 1.04 ± 0.11). The medial compartment demonstrated greater consistency than the lateral (DMO–PMO: r = 0.83 vs. DLO–PLO: r = 0.65). Anterior-to-flexion-arc ratios ranged from 1.43 to 1.68, with within-patient differences substantially larger than those observed within the flexion arc (ALO vs. DLO: Cohen’s d = 5.35; ALO vs. PLO: Cohen’s d = 5.08). Anterior offsets strongly correlated with each other ( r = 0.78–0.81), while inter-compartmental correlations were consistently weaker ( r = 0.62–0.75).The distal and posterior femoral condyles form a geometrically coherent unit that can be approximated using a single radius, whereas the anterior compartment is substantially decoupled from the flexion arc, supporting the use of patient-specific, asymmetric implant systems to better restore native femoral geometry.