Abduction in internal rotation: a test for the diagnosis of axillary nerve palsy

To describe and validate the use of a test of abduction in internal rotation for the assessment of axillary nerve injury.

A total of 14 male patients with a mean age of 29 years (SD ± 6 y), with axillary nerve lesions lasting an average of 6 months, participated. We measured their shoulder range of motion. In the upright position, with the trunk bending forward, we asked our patients to actively extend the shoulder (swallowtail test), and then we extended the shoulders and asked each patient to hold them in that position (deltoid extension lag test). For the abduction in internal rotation test, we asked patients to abduct the shoulder in internal rotation. If full abduction compared with the normal contralateral side was not possible, the examiner passively held the affected limb in maximal abduction and internal rotation. The patient was instructed to maintain the position when the examiner released the limb. In each test, any lag compared with the normal side accounted for deltoid palsy.

All patients exhibited abduction beyond horizontal and full external rotation. The swallowtail test and the deltoid extension lag test identified the axillary nerve lesion in 10 of 14 patients. The abduction in internal rotation test recognized the axillary nerve injury in all 14. The average difference in the range of abduction in internal rotation between the normal and affected side was 37° (abduction lag).

Compensatory abduction in axillary nerve palsy has been attributed to the action of the supraspinatus, biceps, coracobrachialis, and pectoralis major. During abduction in internal rotation, compensatory abduction is impaired, clearly indicating deltoid muscle dysfunction.