Scapula

 Osteology

Scapula is a thin, flat triangular-shaped bone placed on the postero-lateral aspect of thoracic cage . It has 2 surfaces, 3 borders, 3 angles and 3 processes.

Surfaces
1. Costal surface or subscapular fossa
    It is concave and is directed medially and forwards. It is marked by 3 longitudinal ridges. A thick ridge adjoins the lateral border. This part of bone is almost rod like : acts a lever for action of serratus anterior in overhead abduction of the arm.

2. Dorsal surface
    The prominent spine of scapula divides the surface into a smaller supraspinatous fossa and a larger infraspinatous fossa. The depth of the supraspinatous fossa is filled by the supraspinatus muscle.

Borders 1. Superior border

    It is thin and shorter. It presents the suprascapular notch near the root of the coracoid process. The superior border extends from the superior angle laterally towards coracoid process.

2. Lateral border
   This is thick and presents infraglenoid tubercle at the upper end. The lateral or axillary border runs from the inferior angle to the lateral angle of the scapula.

3. Medial border
This is thin and extends from superior to inferior angle. With the arm resting by the side, the medial or vertebral border runs almost parallel to the spinal column.

Angles
1. Superior angle is covered by trapezius
2. Inferior angle is covered by the latissimus dorsi. It moves forwards round the chest, when the arm is abducted. Palpation of the inferior angle provides a convenient method for following the movement of the scapula during arm motion.
3. Lateral or glenoid angle is broad and bears the glenoid cavity or fossa, which is directed forward, laterally and slightly upwards.

Processes
1. Spine or spinuous process is a triangular plate of bone with 3 borders and 2 surfaces. It divides the dorsal surface of the scapula into supraspinous and infraspinous fossae. The posterior border is called the crest of the spine which has upper and lower lips.
2. The acromion has 2 borders, medial and lateral; 2 surfaces and a facet for clavicle.
3. The cracoid process