Radiographic evaluation of ulnar deformity in patients with hereditary multiple osteochondroma and its relationship with radial head dislocation.

Introduction: In patients who have hereditary multiple osteochondroma (HMO), progressive deformity of the forearm skeleton may lead to radial head dislocation. The latter is permanent, painful and causes weakness.

Hypothesis: There is a relationship between the amount of ulnar deformity and the presence of radial head dislocation in patients with HMO.

Materials And Methods: This was a cross-sectional radiographic study comprising an analysis of anterior-posterior (AP) and lateral x-rays of 110 forearms in children having a mean age of 8 years and 4 months who were followed for HMO between 1961 and 2014. Four factors reflecting on the ulnar deformity in the coronal plane were investigated on the AP view and three factors in the sagittal plane were investigated on the lateral view to identify any relationship between ulnar deformity and radial head dislocation. The forearms were separated into two groups: with radial head dislocation (26 cases) and without radial head dislocation (84 cases).

Results: Ulnar bowing, intramedullary angle of ulnar bowing, tangent ulnar angle and overall ulnar angle were significantly higher in the group of children who had a radial head dislocation (0.05 vs 0.03, p<.001; 161 vs 167, p<001; 156 vs 162, p<001; 50 vs 30, p<.001) in univariate and multivariate analyses.

Discussion: Ulnar deformity, evaluated using the method described here, is more often associated with radial head dislocation than other previously published radiological parameters. This provides new insight on this phenomenon and may help to determine which factors are associated with radial head dislocation and how to prevent it.

Conclusion: Ulnar bowing in the context of HMO, especially when evaluated on AP radiographs, is significantly associated with radial head dislocation.

Level Of Evidence: III; case-control study.