Predicting Radial Head Instability in Multiple Hereditary Exostoses (MHE): A Multicenter Analysis of Risk Factors.

Background: Forearm deformity occurs in one third of patients with multiple hereditary exostoses (MHE). Conservative and surgical treatment are aimed at preventing radial head subluxation and/or dislocation. Dislocation has been associated with isolated distal ulnar lesions, radial bowing, and ulnar shortening. Risk factors for radial head subluxation have not been clearly elucidated. This study aimed to identify risk factors for all radial head instability in MHE, to optimize early detection and prevent frank dislocation. Methods: This multicenter retrospective case-control investigation included MHE patients with forearm lesions seen between 2000 and 2017 at 2 tertiary care children's hospitals. Demographic, clinical factors, radiographic measures, and surgical history were quantified. Comparisons were made between forearms that developed radial head instability versus those that remained stable and between those that progressed to radial head subluxation versus those that progressed to dislocation. Results: This study included 171 forearms in 113 patients with MHE, who presented at a mean age of 8.0 years with a median follow-up time of 6.0 years. Nine forearms progressed to radial head subluxation (mean age: 10.2 y), and 24 forearms had radial head dislocation (mean age: 9.9 y). Five subluxations and 3 dislocations occurred despite preventative surgery. Initial radial bowing (7.2% vs. 8.5%,P=0.04), ulnar variance (-5.8% vs. 11.0%,P<0.001), and ulnar shortening (-2.5 vs. 9.1 mm,P=0.04) were predictive of radial head instability. Distal ulnar lesions and more severe ulnar variance (-5.8 vs. -10.6,P<0.001) and shortening (-2.5 vs. 13.2 mm,P=0.02) were associated with an increased risk of radial head subluxation. No significant differences were identified between forearms that progressed to subluxation versus those that progressed to dislocation. Conclusions: Distal ulnar lesions and radiographic measures can be used to determine the risk of radial head instability in MHE. Ulnar variance and shortening are early identifiable risk factors for radial head subluxation that can help guide monitoring and treatment. Radial bowing may be a late predictor of instability.