Overview
The scapula (scapula) is a flat, triangular and elongated bone lying against the lateral wall of the thorax. It has no bony joint with the trunk: the thoracic limb is attached to it by muscles only (synsarcosis), especially the serratus ventralis, which suspends the thorax between the two limbs. In the horse it slopes obliquely from the withers to the point of the shoulder, and its dorsal border is extended by a broad scapular cartilage (cartilago scapulae).
Key features
- Scapular spine (spina scapulae): divides the lateral surface into the supraspinous and infraspinous fossae, filled by the muscles of the same names. In the horse it is low and flattens distally without forming an acromion.
- Tuberosity of the spine (tuber spinae scapulae): a thickening in the middle third of the spine, easily palpated under the skin.
- Costal surface: with the subscapular fossa and the serrated face, where the serratus ventralis attaches.
- Glenoid cavity (cavitas glenoidalis): shallow, articulates with the head of the humerus at the shoulder joint, which has no collateral ligaments: the surrounding muscles take over that role.
- Supraglenoid tubercle (tuberculum supraglenoidale): large and prominent, cranial to the glenoid cavity; origin of the biceps brachii. On its medial side the coracoid process gives origin to the coracobrachialis.
Clinical relevance
- Fractures of the supraglenoid tubercle: from falls or collisions of the shoulder with fixed objects; being intra-articular, they affect the athletic prognosis.
- Atrophy of the supraspinatus and infraspinatus ("sweeney"): from injury to the suprascapular nerve, which wraps around the neck of the scapula and is vulnerable to blows on the point of the shoulder. The spine stands out under the skin and the shoulder may swing outwards when the limb bears weight.
- Osteochondrosis of the shoulder: in young horses it affects the glenoid cavity and the head of the humerus, with lameness and a poor athletic prognosis.