Biomechanical analysis of the annular ligament in Monteggia fractures using finite element models

BACKGROUND: The pathogenesis of Monteggia injuries remains controversial. The current study biomechanically explored the pathological changes during Monteggia fractures using finite element analysis. METHODS: Two cadaveric forearm specimens underwent computed tomography in both the prone and supine positions. The images were imported to Mimics to construct three-dimensional images. The obtained models of the annular ligaments were assembled onto the bones. Two thin gaps were produced at the proximal third of the ulna to simulate a Monteggia fracture. The models were analyzed mechanically. The initial fracture process was simulated by constraining the distal portions of the radius and ulna and the dorsal fracture sites of the ulna. The mechanical changes of the annular ligament in the two positions were observed and compared. RESULTS: In the prone position, the maximum Z-axial displacement of the annular ligament was close to that along the Y-axis, although with a significant difference (P < 0.01). In the supine position, the X-axial displacement dramatically increased (P < 0.01), while it was noticeably decreased along the Z-axis (P < 0.01). CONCLUSIONS: Biomechanical changes may partially explain the pathological changes in the annular ligament during Monteggia fractures; longitudinal displacement of the radial head causes it to slip out of the annular ligament while the ligament remains intact.