Anatomy and supply
The anconeus muscle is a small, triangular muscle located at the elbow. It originates at the dorsal side of the lateral epicondyle of the humerus and inserts at the olecranon of the ulna. The fibers of the origin tendon are further attached to the dorsal joint capsule. The muscle lies superficially and can be easily palpated at the dorsal, lateral side of the forearm near the elbow.
The anconeus is supplied by a motor branch of the radial nerve (C6-C8), which arises at the radial sulcus of the humerus, continues through the medial head of the triceps and finally reaches the muscle distally. Both morphologically and functionally the anconeus constitutes a continuation of the triceps. Not only are they innervated by the same nerve, but also both muscles are very often either partly or completely blended together.
Functionally the anconeus fulfills the same tasks at the elbow as the triceps muscle. Its contraction leads to the extension of the forearm. Furthermore, it keeps the tension of the dorsal joint capsule, thus preventing damages during hyperextension. It is believed that the anconeus has the additional function of stabilizing the ulna, especially during pronation movements of the forearm.
An anatomical variation of the anconeus is found in up to one third of all humans. Even though most are harmless, there is one variation which can be considered clinically relevant, namely the anconeus epitrochlearis muscle. This muscle originates – contrary to the “normal” variation - at the medial epicondyle of the humerus, thus crossing the ulnar groove of the humerus bone where the ulnar nerve lies. In cases of hypertrophy (e.g. in weightlifters) the anconeus epitrochlearis can therefore compress the nerve leading to numbness at the ulnar border of the hand, the little and ring fingers, as well as elbow and forearm pain (cubital tunnel syndrome).