Anatomy of The Scapula

Scapula is bone of shoulder girdle. It serves as connection between upper limb and clavicle. Its acromion process articulates with clavicle at lateral end of clavicle to form acromioclavicular joint. It also forms glenohumeral joint, popularly known as shoulder joint through its glenoid cavity with head of humerus. It has two surfaces, three borders, three angles and three processes.

The surfaces

1. The costal surface ( that abuts thorax) is concave and is directed medially and forwards. It is marked by three longitudinal ridges. Another thick ridge adjoins the lateral border. This part of the bone is almost rod like: it acts as a lever for the action of the serratus anterior in overhead abduction of the arm.
2. The dorsal ( that can be palpated from back) surface gives attachment to the spine of the scapula which divides the surface into a smaller supraspinous fossa and a larger infraspinous fossa. The two fossae are connected by the spinoglenoid notch, situated lateral to the root of the spine.

The borders

1. The superior border is thin and short. Near the root of the coracoids process it presents the suprascapular notch.
2. The lateral border is thick. At the upper end it presents the infraglenoid tubercle.
3. The medial border is thin. It extends from the superior angle to the inferior angle.

The angles

1. The superior angle is covered by the trapezius.
2. The inferior angle is covered by the latissimus dorsi. It moves forward round the chest when the arm is abducted.
3. The lateral (or glenoid) angle is broad and bears the glenoid cavity (or fossa) which is directed forwards, laterally and slightly upwards.

The processes

1. The spine (or spinous process) is triangular plate of bone with three borders and 2 surfaces. It divides the dorsal surface of the scapula into the supraspinous and infraspinous fossae. Its posterior border is called the crest of the spine. The crest has upper and lower lips.
2. The acromion has two borders, medial and lateral; two surfaces, superior and inferior, and a facet for the clavicle.
3. The coracoids process is directed forwards and slightly laterally.

Determination of the side

1. The lateral (glenoid) angle is large and bears the glenoid cavity.
2. The dorsal surface is convex and is divided by the triangular spine into the supraspinous and infraspinous fossae. The costal surface is concave to fit on the convex chest wall.
3. The lateral thickest border runs from teh glenoid cavity above to the inferior angle below.

Scapula is usually fractured in trauma around shoulder. Usually it responds very well to conservative mode of treatments.

Text adapted from: Human Anatomy by BD Chaurasia

Image Credit: Wikipedia