Overview
The scapula is a flat, triangular bone lying against the lateral wall of the cranial thorax. It has no bony joint with the trunk: the muscles of the shoulder girdle (serratus ventralis, rhomboideus, trapezius and others) hold it in place, which lets it glide widely during walking and jumping. Distally it articulates with the humerus at the shoulder joint.
Key features
- Spine of the scapula (spina scapulae): a ridge on the lateral surface that divides it into the supraspinous fossa (cranial) and the infraspinous fossa (caudal), filled by the muscles of the same names.
- Acromion: the distal end of the spine. In the cat it carries a hamate process (processus hamatus), directed ventrally, and a suprahamate process (processus suprahamatus), directed caudally; they give attachment to the acromial part of the deltoideus and to the omotransversarius.
- Medial (costal) surface: with the subscapular fossa for the subscapularis and the serrated face where the serratus ventralis inserts.
- Dorsal border: extended by the scapular cartilage.
- Glenoid cavity (cavitas glenoidalis): shallow articular surface for the head of the humerus.
- Supraglenoid tubercle: origin of the biceps brachii; medial to it the small coracoid process gives origin to the coracobrachialis.
Clinical relevance
- Fractures: uncommon, because the scapula is protected by a thick layer of muscle; they occur in high-energy trauma.
- Dorsal scapular luxation: rupture of the serratus ventralis and the other muscles that fix the scapula to the trunk, described in cats after falls or trauma, makes the dorsal border rise above the line of the back when the limb bears weight.
- Radiography: the scapula overlaps the spine and the first ribs on lateral thoracic views.