RESUMEN
Objective : Causes of nontraumatic posterior interosseous nerve (PIN) palsy include space-occupying lesions, constrictions of the PIN, and supinator syndrome. The purpose of this study was to identify these causes using Ultrasonography (US). Methods : We performed US in seven cases (seven elbows) with palsy and examined the PIN and surrounding structures. Results : We identified the three causes by the following US findings : 1) A space-occupying lesion in two elbows. Both were low-echoic and diagnosed as ganglion. In these two cases, the PIN was elevated by the lesion and compressed against the arcade of Frohse. 2) A diffusely swollen PIN with constrictions was found in three cases. 3) A PIN showing a reduction in caliber beneath and a swelling (pseudoneuroma) proximal to the arcade of Frohse, compatible with supinator syndrome was also identified. Conclusion : US is useful for the diagnosis of nontraumatic PIN palsy.