An Evaluation of Forearm Deformities in Hereditary Multiple Exostoses: Factors Associated With Radial Head Dislocation and Comprehensive Classification.

ABSTRACT

PURPOSE: This study attempted to evaluate a series of patients with hereditary multiple exostoses (HME) who could not be categorized according to the widely accepted Masada classification and to identify radiographic variables such as radial bowing, ulnar shortening, ulnar variance, radial articular angle, and carpal slip predictive of deformity. METHODS: We retrospectively reviewed data on 102 upper limbs of 53 pediatric patients with HME. Demographics, site of forearm involvement, and radiographic parameters were documented. Patients with exostoses of the forearms were categorized into 6 groups based on location of the exostoses and presence or absence of a dislocated radial head. Proportional ulnar shortening was calculated as the ratio of ulnar length to radial length. RESULTS: According to the Masada classification, 4 limbs were normal, 10 were type I, 2 were type II, and 24 were type III. Sixty-six limbs were unclassifiable. We classified those 66 limbs using a modification of the Masada classification. Of the 106 limbs, 11 (10.3%) had a dislocated radial head. Based on the radiographic analysis, patients with proportional ulnar shortening of less than 0.9 had a higher risk of radial head dislocation than did those with proportional ulnar shortening of 0.9 or greater. Patients with radial bowing greater than 8.1% showed a higher frequency of radial head dislocation than did those with radial bowing of 8.1% or less. Exostoses of both the distal radius and ulna tended to increase the rate of radial head dislocation. A greater amount of negative ulnar variance caused more radial bowing and a greater radioarticular angle. CONCLUSIONS: We propose a new comprehensive forearm classification for patients with HME. Proportional ulnar shortening less than 0.9 and radial bowing 8.1% or greater can be used to predict the risk of radial head dislocation. TYPE OF STUDY/LEVEL OF EVIDENCE Prognostic IV.