Three-dimensional lower limb alignment in healthy Chinese adults: Gender-specific phenotypes and ethnic variations for personalised correction

Purpose: To develop a personalised three-dimensional (3D) lower-limb alignment classification system from a healthy Chinese adult population. Based on full-length computed tomography (CT) scans, key alignment parameters in the coronal, sagittal and transverse planes were analysed to establish gender-specific anatomical phenotypes. This system is designed to provide a normative reference for individualised planning in lower-limb alignment correction procedures such as total knee arthroplasty (TKA) and high tibial osteotomy (HTO). Methods: Full-length lower-limb CT scans were obtained from 554 healthy participants (males: 252, females: 302; age: 22–77 years [mean: 47.7 ± 10.6]), and 3D models were reconstructed. Eleven alignment parameters were measured from the models across the sagittal, coronal and transverse planes. Plane-specific classifications were developed and integrated into a combined 3D phenotype (CSTA). Results: All parameters except for joint line obliquity angle showed statistically significant gender-based differences. The classification system comprises nine sagittal plane types (S1–S9), nine coronal plane types (C1–C9) and three transverse plane types (T1–T3). The most frequent 3D phenotype in males was C1S6T1 (Apex distal/Varus—Moderate/Flexion—External rotation, 10.0%), while in females it was C2S5T2 (Apex distal/Neutral—Moderate/neutral—Neutral, 8.6%). Compared with Western populations, distinct anatomical characteristics were observed in Chinese individuals, including greater femoral anteversion, higher tibial torsion, and a more pronounced tendency towards sagittal-plane flexion. Conclusion: This study systematically establishes a 3D lower-limb alignment classification system for healthy Chinese adults, highlighting gender and ethnicity‑specific alignment characteristics. The proposed classification provides an anatomical basis for personalised surgical planning in procedures such as TKA and HTO, and contributes to advancing lower limb alignment correction towards precision and individualised care. Level of Evidence: NA, basic science studies.