Forearm and elbow injury: The influence of rotational position

Background: The purpose of this study was to develop an axial loading forearm fracture model and to determine the influence of forearm rotation on the fracture pattern. Methods: Twenty-six cadaveric arms were thawed in saline solution. Pressure-sensitive film was sealed and was placed through a lateral arthrotomy into the radiocapitellar joint. The arm was potted at the proximal part of the humerus with the elbow in extension. Rotational range of motion was measured with use of a goniometer starting from a supinated position (0degrees). Specimens were placed in a vertical position at various angles of forearm rotation, and a 27-kg mass was raised to 90 cm and was dropped onto the distal part of the radius. The pressure film was removed and was analyzed to determine the radiocapitellar joint contact area following impact. Each arm was dissected, and the injury pattern was assessed. Results: Both-bone forearm fractures (proximal radial fractures with concomitant distal ulnar fractures) occurred at 5degrees +/- 2.6degrees of rotation, isolated radial head fractures occurred at 44.4degrees +/- 5.2degrees of rotation, and Essex-Lopresti fractures (radial head fractures with tearing of the interosseous membrane) occurred at 70degrees +/- 25.2degrees of rotation. The distribution of Essex-Lopresti and radial head fractures was significantly different at a cutpoint of 540 of forearm rotation (p = 0.009), and the distribution of radial head fractures and both-bone forearm fractures was significantly different at a cutpoint of 100 of forearm rotation (p = 0.001). The percent contact area of the radial head varied with the injury pattern (p = 0.029). Marginal radial head fractures occurred at 46.7degrees +/- 6.6degrees of rotation with a contact area of 30.9% +/- 8.6%, while comminuted radial head fractures occurred at 74.4degrees +/- 27.2degrees of rotation with a contact area of 53.9% +/- 8.3%. Conclusion: The amount of forearm rotation at the time of axial load impact directly influenced the injury pattern. Furthermore, the radial head contact area and the fracture severity increased in pronation compared with supination. Clinical Relevance: This model provides the basis for investigating the mechanisms involved in forearm and elbow trauma under the application of an axial impact load. Using this model, we established the relationship between rotation and the fracture pattern incurred by the forearm and radial head.