Apex Posterior Overcorrection of the Ulna Increases Radial Head Stability in Anterior Monteggia Fractures: An In Vitro Biomechanical Study.

Abstract

Anterior radial head instability may persist with anatomic restoration of the ulna in anterior Monteggia fractures, leading to poor outcomes. The purpose of this study was to evaluate the effect of apex posterior ulnar overcorrection on radial head (RH) stability in the setting of anterior Monteggia fractures. It was hypothesized that increasing apex posterior angulation of the ulna, as well as a supinated forearm position, would decrease anterior RH translation. Sequential static biceps loading was applied to nine cadaveric arms using an elbow simulator with the elbow positioned in 90° of flexion in neutral, pronation, and supination. Testing was first performed on the arm with all soft tissues intact, followed by sectioning of soft tissue stabilizers of the proximal radius, including the central and proximal interosseous membrane, and the annular and quadrate ligaments. A custom fixation device was then employed to simulate progressive apex posterior angulation (0°, 10°, 20°, and 30°) of the ulna. Anterior translation of the RH was quantified using a modified radiocapitellar ratio (RCR), with 0% corresponding to no anterior translation and 100% corresponding to dislocation. The intact soft tissue state exhibited the lowest RCR in neutral, pronation, and supination. After sectioning the soft tissue stabilizers, increased RH stability was observed with increasing posterior ulnar angulation for all forearm orientations. Pronation of the forearm resulted in a considerable reduction in the RCR compared to both neutral and supination for all simulated fracture states, but not with the intact soft tissue state. The results from this study suggest that posterior overcorrection of the ulna and a pronated forearm position enhance RH stability. Apex posterior overcorrection of the ulna can be used to treat radial head instability in anterior Monteggia fractures. These findings also suggest pronation may be the optimal position of immobilization in anterior Monteggia fractures.