How close is the axillary nerve to the inferior glenoid? A magnetic resonance study of normal and arthritic shoulders.

Abstract

Axillary nerve injury is a major complication of shoulder surgery during glenoid exposure. The aim of this study was to measure the mean distance between the inferior glenoid and the axillary nerve in healthy shoulders and then to compare this distance between osteoarthritic and rotator cuff deficient glenohumeral joints. The magnetic resonance images of 50 patients with normal glenohumeral joints were reviewed. The infra-glenoid tubercle was determined as a fixed point and the distance to the axillary nerve was measured. Two separate assessors measured on the same sagittal sections. With a study power of 80%, the sample needed in each comparison group was 28 patients. Measurements were then performed on scans in patients with osteoarthritis and cuff tear arthropathy. The mean distance was compared between groups. The mean distance between the infra-glenoid tubercle and axillary nerve was 12mm (standard deviation, SD, 5.6mm) in normal shoulders, 10.6mm (SD 5.4mm) in shoulders with osteoarthritis and 9.7mm (SD 3.7mm) in those with cuff tear arthropathy. For this sample size of 50 patients with a confidence interval of 95%, the mean range is 12mm (95% CI 10.4-13.6). A comparison between normal shoulder and osteoarthritis showed a p-value of 0.3, and between normal and cuff tear arthropathy a p-value of 0.06. This was not statistically significant. The axillary nerve lies on average 12mm from the infra-glenoid tubercle. The presence of inferior osteophytes in glenohumeral osteoarthritis and the proximal migration of humeral head in cuff tear arthropathy does not seem to alter the course of the nerve significantly in relation to the inferior glenoid tubercle.