Radiological findings in posteromedial rotatory instability of the elbow and their application to treatment

Aims: Early identification and appropriate surgery are essential in the management of patients with posteromedial rotatory instability of the elbow to prevent the development of early post-traumatic osteoarthritis. The aim of this study was analyze the radiological findings in order to suggest appropriate treatment strategies. Methods: A total of 58 patients with posteromedial rotatory instability of the elbow, with available 3D CT and MRI scans, were included. We investigated the size of the anteromedial coronoid facet fracture and the patterns of injury to the lateral collateral ligament complex and ulnar collateral ligament, relating them to the O'Driscoll subtypes 2-1, 2-2, and 2-3 of injury. Results: Subtypes 2-1, 2-2, and 2-3 comprised eight, 41, and nine patients, respectively. The mean size of the coronoid fracture significantly increased from subtype 2-1 (3.2 mm (SD 1.5)) to 2-3 (10.0 mm (SD 2.2mm)) (p < 0.001). The rate of rupture of the lateral ligament and the requirement for repair decreased significantly from 100% in subtype 2-1 to 33% in subtype 2-3 (p = 0.038, p = 0.005). The rate of rupture of the posterior bundle of the ulnar ligament increased significantly from 25% in subtype 2-1 to 100% in subtype 2-3 (p = 0.006). Conclusion: There are distinct patterns of radiological injury in the subtypes of posteromedial instability. Subtype 2-1 is primarily associated with substantial lateral ligamentous injury, whereas subtype 2-3 features larger coronoid fractures and an increased rate of associated injury to the posterior bundle of the ulnar ligament; subtype 2-2 is intermediate. These findings inform a proposed algorithm for the surgical treatment: lateral ligamentous repair is key for 2-1, and fixation of the coronoid fracture fixation is key for 2-3, with intraoperative assessment guiding further steps. This observational study establishes a theoretical framework for the management of these patients, which will require validation in the future.