Diaphyseal humerus fractures: natural history and occurrence of nonunion.

We reviewed 38 fractures of the humeral shaft which had been treated non-operatively to identify factors prognostic of nonunion. Of these, 23 healed uneventfully and 15 progressed to nonunion. Factors prognostic of nonunion included long oblique fracture pattern, alcohol abuse, and obesity. In patients with these risk factors, lack of clinical and radiographic evidence of healing 8 to 10 weeks post-injury suggests an impending nonunion, and operative intervention should be considered.