Elliptical defects create a more adverse biomechanical environment than circular defects in osteochondral lesion of...

Osteochondral lesion of the talus (OLT) is a common ankle injury that may disturb the biomechanical environment and contribute to progressive articular degeneration. However, in clinical practice, OLT is typically elliptical, whereas most biomechanical studies modeled OLTs as circular defects. This study aimed to compare circular and elliptical OLT defects of different sizes and locations using finite element analysis.

A subject-specific ankle finite element model was reconstructed from CT data. Full-thickness circular and elliptical defects ranging from 25 to 200 mm² were created in zones 4 and 6 and analyzed under three gait phases. Elliptical defects were defined with an anteroposterior-to-mediolateral axis ratio of 1.5:1. Peak von Mises stress, peak stress location, and regional stress distribution were analyzed.

Compared with circular defects, elliptical defects generally produced higher peak stress and a more adverse redistribution pattern. In zone 4, differences between shapes became more evident in larger defects, and at 200 mm², peak stress in circular defects was 3.77, 4.16, and 5.02 MPa, compared with 4.37, 4.85, and 5.85 MPa in elliptical defects across all gait phases. A similar pattern was observed in zone 6, with elliptical defects also producing higher peak stress than circular defects. These differences were more evident in zone 4 during midstance and push off and were consistently observed in zone 6 across all gait phases. In zone 4, elliptical defects caused the global peak stress to shift from zone 3 to zone 1 at a smaller defect size (150 vs. 175 mm²). Elliptical defects also showed a smaller distance between the local peak stress and defect edge than circular defects (2.10 vs. 2.24 mm). Stress redistribution favored the anterior-posterior direction in zone 4 for both shapes, whereas in zone 6 this directional pattern was less consistent, particularly in elliptical defects.

Defect shape substantially alters the biomechanical environment of OLT. Compared with circular defects, elliptical defects produce greater stress concentration, earlier stress redistribution, and a more unfavorable stress pattern, especially in larger lesions. These findings suggest that defect shape should be considered in biomechanical assessment and clinical evaluation.