Overview
The humerus is the bone of the arm. Its shaft is slightly twisted in an S shape, with the head facing caudally at the proximal end and the trochlea facing cranially at the distal end. It is a strong bone that carries the insertions of most muscles moving the shoulder and elbow.
Proximal end
- Head (caput humeri): convex articular surface, larger than the glenoid cavity, facing caudally.
- Greater tubercle (tuberculum majus): lateral, insertion of the supraspinatus and infraspinatus muscles. It is palpable and forms the "point of the shoulder".
- Lesser tubercle (tuberculum minus): medial, insertion of the subscapularis.
- Intertubercular groove: between both tubercles, carrying the tendon of the biceps brachii.
Shaft and distal end
- Deltoid tuberosity: prominent lateral ridge where the deltoideus inserts.
- Humeral condyle: made of the trochlea (medial, articulating with ulna and radius) and the capitulum (lateral, articulating with the radius).
- Olecranon fossa (caudal) and radial fossa (cranial), connected in the dog by the supratrochlear foramen.
- Medial and lateral epicondyles: origin of the carpal and digital flexors and extensors, respectively.
Clinical relevance
The proximal humerus is, together with the distal radius, the most common site of osteosarcoma in large breeds ("away from the elbow, toward the knee"). Humeral condylar fractures are typical in chondrodystrophic puppies, and incomplete ossification of the humeral condyle (IOHC) predisposes Spaniels to fractures. The humeral head is the classic site of shoulder osteochondrosis.