Effect of osteochondroma location on forearm deformity in patients with multiple hereditary osteochondromatosis.

Purpose: Multiple hereditary osteochondromatosis (MHO) is an autosomal-dominant skeletal dysplasia that may result in forearm deformity. The purpose of this study was 2-fold: to describe the natural history of forearm deformity in patients with MHO, with particular attention to those who develop radial head dislocation, and to determine predictors of deformity.

Methods: We retrospectively reviewed charts of all patients with MHO evaluated at our institution. Patients with the presence of a radiographically visible osteochondroma in the forearm were divided into 5 groups or types based on location of the osteochondroma(s). Radiographic measurements included radial articular angle, percent ulnar variance, radial bow, radial length, ulnar length, and ulnar bow. The predictive values of each measure were statistically evaluated for each type with relation to radial head dislocation.

Results: Of 146 patients with MHO, 102 patients (70%) had forearm involvement. Appropriate anteroposterior and lateral radiographs were available on 48 patients (76 forearms). Average age at initial radiographic evaluation was 12 years (range, 2-18 y). Average follow-up period was 7 years (range 1-19 y). Thirteen forearms demonstrated radial head dislocation, with all but 1 reported in the type 1 limbs (solitary distal ulna osteochondroma). Radial head dislocation was noted in 34% (12/35 forearms) of type 1 limbs.

Conclusions: Forearms with isolated osteochondromas of the distal ulna are the ones most likely to develop radial head dislocation. Because the ulna growth is disproportionately less than radial growth, the soft tissues may act as a tether, linking the distal radius and ulna, and lead to radial head dislocation. Changes in radiographic measurements may predict limbs at risk for radial head dislocation.