The anconeus is a very tiny muscle found on the outside of the elbow, attaching the humerus to the ulna. Functionally, it is very similar to the tricep where it is involved in the extension of the elbow and stabilizes movements of the elbow joint. There is an anatomical variation of the anconeus that can be found in only one third of all humans, called the anconeus epitrochlearis. While similar in size and shape to the anconeus, the anconeus epitrochlearis attaches from the inside of the humerus to the ulna. When it is present, it replaces the Osborne’s ligament, a thin ligament that is found in the same position. Its function is the opposite of the anconeus, where it is tightened when the elbow is flexed but relaxes when the forearm is extended.
An issue found with the anconeus epitrochlearis may be because it originates from the medial side of the humerus, it crosses on top of the ulnar nerve. For those who train their biceps and forearm muscles like weightlifters, hypertrophy of the anconeus epitrochlearis may cause an impingement of the ulnar nerve. This may cause numbness and pain during elbow flexion, and chronic pain for those with increased muscle tone. It is also a cause of cubital tunnel syndrome, which leads to numbness and weakness in the 4th and 5th fingers. For those with pains and numbness from impingement, surgery can be done to remove the anconeus epitrochlearis and no functions will be limited due to its removal.