The anconeus muscle revisited: double innervation pattern and its clinical implications

The aim of the present study is to describe in detail the morphology and innervation pattern of the anconeus muscle, bearing in mind clinical implications such as iatrogenic injuries during surgical elbow approaches. A cadaveric study was performed; 56 elbows from 28 formalin-fixed cadavers belonging to the Anatomy Department of Universidad Complutense of Madrid were dissected. The triceps–anconeus nerve was located and dissected. A second innervation to the anconeus muscle from a branch of the posterior interosseous nerve (PIN) was occasionally detected. Taking the lateral epicondyle as a landmark, the entry points of both nerves in the muscle were referenced, the triceps–anconeus nerve was referenced at 0°, 30°, 45°, 70° and 90° of elbow flexion, and the PIN branch at 0°. Anconeus muscle was present in all specimens. The triceps–anconeus nerve was present in all of the dissected elbows. A branch from PIN to the anconeus muscle was present in 38 of the 54 elbows (70.4%). There were statistically significant differences in all measurements regarding the specimens’ gender, being higher for men. There is evidence of a high frequency of a double innervation pattern for the anconeus muscle: the main branch of triceps–anconeus muscle depending on the radial nerve, which is liable to being damaged during posterior elbow approaches, and a secondary branch depending on the PIN. There are very few references to this finding in Anatomical literature and none with such a large sample size.