Supracondylar Process of the Humerus

The supracondylar process of the humerus is a bony projection from the anteromedial aspect of the distal humeral diaphysis that can be shaped as a spine or a tubercle. It is typically 5 cm - 7 cm proximal to the medial epicondyle and is often connected to the medial epicondyle by a fibrous band (ligament of Struthers). Seen in about 1% of the population, the supracondylar process is more commonly seen in Caucasians, in males, and on the left.

Synonyms include: supracondylar spur, supracondyloid process, supratrochlear process, epicondylar process, epicondylic process, and avian spur.

In some cases, a fibrous band called the ligament of Struthers arises from the supracondylar process and attaches to the medial epicondyle, forming a foramen through which the median nerve and brachial artery may pass. A case of the neurovascular bundle passing superficial to the ligament of Struthers has also been reported.

The tubercle shape of the supracondylar process is more likely to be associated with the ligament of Struthers than the spine shape. The supracondylar process is also associated with a high origin of the pronator teres muscle, which may have an attachment to the ligament of Struthers or the process itself. Some of the lower fibers of the coracobrachialis muscle may also arise from the supracondylar process or ligament of Struthers.

While usually asymptomatic, patients may present with symptoms related to a fracture of the process or compression of the median nerve and brachial artery by the foramen formed by the ligament of Struthers. Less commonly, there may be compression of a variant ulnar artery and rarely compression of the ulnar nerve. Symptoms tend to increase with pronation of the forearm.

Radiographs reveal a bony projection arising from the anteromedial margin of the distal humerus that is best demonstrated on an oblique, internally rotated projection of the humerus. Unlike aosteochondromas, which are oriented away from the joint, the supracondylar process is directed toward the joint.

The process seems to be a homologue of a bony arch found in the same location on the humeri of cats, certain monkeys, and some other animals. The ligament of Struthers may be a remnant of the tendon of the latissimo-condyloideus, a muscle that extends from the humeral attachment of the latissimus dorsi to the medial epicondyle in certain climbing animals. I couldn't find a reference describing why the process is referred to as an avian spur.

References

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• Gunther SF, DiPasquale D, Martin R. Struthers' ligament and associated median nerve variations in a cadaveric specimen. Yale J Biol Med. 1993 May-Jun;66(3):203-8.
• Jelev L, Georgiev GP. Unusual high-origin of the pronator teres muscle from a Struthers' ligament coexisting with a variation of the musculocutaneous nerve. Rom J Morphol Embryol. 2009;50(3):497-9.
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• Yazar F, Acar HI. Supracondylar process with a high origin of the radial artery. Clin Anat. 2006 Nov;19(8):730-1.