Teres minor innervation in the context of isolated muscle atrophy

Teres minor atrophy occurs either in isolation, associated with other rotator cuff muscle pathologies or in quadrilateral space syndrome. In the latter condition, compression of the axillary nerve is the likely cause; however, the anatomy of the nerve to teres minor and how this may relate to isolated teres minor atrophy have not been extensively investigated. In light of the significance of teres minor atrophy in shoulder pathology, we performed a combined radiological and anatomical study of teres minor and its nerve supply. Cadaveric dissection of nine shoulder specimens from eight cadavers was performed to investigate the anatomical variability in course, length and branching pattern of both the teres minor nerve and the axillary nerve. Radiological imaging and reports were analysed on all shoulder magnetic resonance images performed over a 1-week period at four radiology clinic locations in an attempt to identify the incidence of isolated teres minor atrophy and review teres minor atrophy in association with other shoulder pathology. Finally, we studied a case of isolated teres minor atrophy identified during a routine undergraduate dissection class. Considerable anatomical variation was noticed in cadaver dissections in the nerve(s) supplying teres minor muscle revealing several various points where it may be vulnerable to impingement or injury at along its course. Analysis of 61 shoulder MR images revealed two patients with shoulder complaints that had isolated teres minor atrophy. Case-based study of these two male patients revealed other associated shoulder injury but the presentation was markedly different and clinically distinct from quadrilateral space syndrome. Isolated teres minor atrophy is a relatively common shoulder pathology which appears to be clinically distinct from other syndromes with rotator cuff muscle atrophy including quadrilateral space syndrome. The exact aetiology is unknown but cadaveric dissection in this study suggests the considerable anatomical variation in both the origin and length of teres minor nerve(s) increase the risk of impingement and subsequent isolated teres minor atrophy.