Radius Pull Test: Predictor of Longitudinal Forearm Instability

Background: Longitudinal instability of the forearm (the Essex-Lopresti lesion) following radial head excision may be difficult to detect. This cadaveric study examines a stress test that can be performed in the operating room to identify injury to the ligamentous structures of the forearm.Methods: Twelve cadaveric upper extremities were randomized into two groups and underwent radial head resection. Group 1 underwent sequential transection of the triangular fibrocartilage complex and the interosseous membrane. Group 2 underwent sequential transection of the interosseous membrane and the triangular fibrocartilage complex. Ulnar variance and radial migration were examined with use of fluoroscopy of the wrist before, during, and after the application of a 9.1-kg load via longitudinal traction on the proximal part of the radius.Results: Group 1 demonstrated no significant changes in proximal radial migration with load (compared with the findings after radial head resection alone) after transection of the triangular fibrocartilage complex. However, Group 2 demonstrated significant changes in proximal radial migration with load after transection of the interosseous membrane (p = 0.03; median, 3.5 mm). In both groups, transection of both the triangular fibrocartilage complex and the interosseous membrane resulted in significant changes in proximal radial migration with load (p = 0.001; median, 9.5 mm). When the load was removed, specimens were ulnar positive (median, 3.0 mm), with no specimen returning to the preload position of ulnar variance (p = 0.001).Conclusion: After radial head resection, 3 mm of proximal radial migration with longitudinal traction indicated disruption of the interosseous membrane. In all specimens, proximal radial migration of ≥6 mm with load indicated gross longitudinal instability with disruption of all ligamentous structures of the forearm.Clinical Relevance: Early detection of longitudinal instability of the forearm is essential for successful management. If radial head resection is necessary, longitudinal traction on the proximal part of the radius may provide useful information regarding the ligamentous support of the forearm and assist in deciding whether to simply excise or to repair or replace the radial head.