Overview
The humerus is the bone of the arm. In the cat it is long, slender and relatively straight compared with the dog's. Proximally it forms the shoulder joint with the glenoid cavity of the scapula, and distally the elbow joint with the radius and ulna.
Proximal end
- Head (caput humeri): convex articular surface facing caudally, larger than the glenoid cavity.
- Greater tubercle (tuberculum majus): lateral, insertion of the supraspinatus and infraspinatus; it is palpable and forms the "point of the shoulder".
- Lesser tubercle (tuberculum minus): medial, insertion of the subscapularis.
- Intertubercular groove: between the two tubercles, carrying the tendon of origin of the biceps brachii.
Shaft
- Deltoid tuberosity and crest of the humerus: on the lateral and cranial surfaces, insertion of the deltoideus and the pectoral muscles.
- Groove for the brachialis: spirals along the lateral surface; it holds the brachialis muscle and the radial nerve, which crosses the bone in its distal third.
Distal end
- Humeral condyle: formed by the trochlea (medial, articulates with the ulna) and the capitulum (lateral, articulates with the radius).
- Olecranon fossa: caudal, receives the olecranon of the ulna when the elbow extends. Unlike the dog, the cat has no supratrochlear foramen.
- Supracondylar foramen (foramen supracondylare): an opening on the medial side of the distal end, proximal to the medial epicondyle, characteristic of the cat. The median nerve and the brachial artery pass through it.
- Medial and lateral epicondyles: origin of the flexor and extensor muscles of the carpus and digits, respectively.
Clinical relevance
- Fractures: diaphyseal and supracondylar fractures after trauma. In the medial approach to the distal humerus and when placing implants, the median nerve and brachial artery must be protected where they pass through the supracondylar foramen; the radial nerve is at risk in diaphyseal fractures.
- Osteosarcoma: the proximal humerus is one of the appendicular sites in the cat. Feline osteosarcoma metastasises far less often than canine osteosarcoma, so amputation can give long survival.
- Osteoarthritis: the elbow is, with the hip, the joint most affected by degenerative joint disease in older cats; signs are often subtle (not jumping, grooming less).