Overview
The humerus (humerus) is the bone of the arm. It articulates proximally with the scapula at the shoulder joint and distally with the radius and ulna at the elbow joint. In the horse it is short and thick, with a shaft that looks twisted because of the spiral groove of the brachialis, and it is almost entirely covered by muscle.
Proximal end
- Head (caput humeri): caudal, articulates with the glenoid cavity.
- Greater and lesser tubercles: lateral and medial, each divided into a cranial and a caudal part. The caudal part of the greater tubercle forms the palpable point of the shoulder.
- Intermediate tubercle (tuberculum intermedium): unique to the horse, between the other two; it divides the intertubercular groove into two channels through which the tendon of origin of the biceps passes, cushioned by the intertubercular bursa (bursa intertubercularis).
Shaft and distal end
- Deltoid tuberosity (tuberositas deltoidea): large and palpable on the lateral surface of the shaft; insertion of the deltoideus.
- Teres major tuberosity: on the medial surface, insertion of the teres major and latissimus dorsi.
- Brachial groove: spirals across the lateral surface and holds the brachialis and the radial nerve.
- Condyle (condylus humeri): trochlea-shaped distal articular surface for the radius and ulna.
- Olecranon fossa: caudal and deep, receives the anconeal process of the ulna when the elbow is extended.
- Lateral and medial epicondyles: origin of the extensors and flexors of the carpus and digits, respectively.
Clinical relevance
- Stress fractures: of the neck and shaft of the humerus in young racehorses in training; if missed they can become complete.
- Complete fractures: from falls or kicks; the limb takes on a dropped elbow posture, also seen in radial nerve paralysis and olecranon fractures.
- Intertubercular bursitis: inflammation or infection of the bursa of the biceps tendon, with weight-bearing lameness and pain on pressure over the point of the shoulder.