The anconeus epitrochlearis (epitrochleoanconeus muscle) is an accessory muscle present in 2-28% of individuals, forming an anomalous muscular band across the cubital tunnel from the medial epicondyle to the olecranon. When present it replaces or supplements the Osborne ligament (cubital tunnel retinaculum) as the roof of the cubital tunnel, creating a rigid muscular compression on the ulnar nerve during elbow flexion.
| Origin | Medial epicondyle of the humerus (epitrochlea) |
|---|---|
| Insertion | Medial border of the olecranon, blending with the deep fascia of the cubital tunnel |
| Nerve Supply | Ulnar nerve (C8-T1), from the branch that passes through the muscle |
| Blood Supply | Posterior recurrent ulnar artery |
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When present it reinforces the roof of the cubital tunnel and may assist the triceps slightly in elbow extension.
The anconeus epitrochlearis is the most clinically significant accessory muscle in the upper limb because it directly causes ulnar nerve compression (cubital tunnel syndrome) when present. The muscle is identified on MRI as an accessory muscle mass in the cubital tunnel. Surgical release requires division of the entire muscle to decompress the ulnar nerve; simple retinaculum release is insufficient. The prevalence is higher in symptomatic cubital tunnel patients than in the general population, suggesting it is a significant cause of ulnar neuropathy.
When present it can sometimes be felt as a small band or fullness bridging the groove between the medial epicondyle and the olecranon, over the ulnar nerve, becoming firmer as the elbow is extended against resistance.
An anconeus epitrochlearis spanning the cubital tunnel compresses the ulnar nerve during elbow flexion producing cubital tunnel syndrome; MRI demonstrates the accessory muscle as a soft tissue mass deep to the medial epicondyle, and surgical release requires complete division of the accessory muscle belly rather than simple retinaculum release.
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