Posterior interosseous nerve discontinuity due to compression by lipoma: report of 2 cases.

Paralysis of the posterior interosseous nerve (PIN) secondary to compression is a rare clinical condition. Entrapment neuropathy may occur at fibrous bands at the proximal, middle, or distal edge of the supinator. Tumors are a relatively rare but well-known potential cause. The authors present 2 cases of PIN lesions in which compression by a benign lipoma at the level of the elbow resulted in near transection (discontinuity) of the nerve. They hypothesize a mechanism-a "sandwich effect"-by which compression was produced from below by the mass and from above by a fibrous band in the supinator muscle (i.e., the leading edge of the proximal supinator muscle [arcade of Fröhse] in one patient and the distal edge of the supinator muscle in the other). A Grade V Sunderland nerve lesion resulted from the advanced, chronic compression. The authors are unaware of a similar case with such an advanced pathoanatomical finding.