Parts Of Scapula

The scapula, commonly known as the shoulder blade, is a triangular, flat bone located on the upper back, playing a crucial role in the shoulder's movement and stability. It serves as a connection between the humerus (upper arm bone) and the clavicle (collarbone) and provides attachment points for numerous muscles that facilitate shoulder motion. Key features of the scapula include the prominent spine, which divides its back surface into the supraspinous and infraspinous fossae, and the acromion, which forms the highest point of the shoulder. Other essential structures include the glenoid cavity, where the scapula articulates with the humerus to form the shoulder joint, and the coracoid process, a hook-like projection on the front of the scapula. The scapula’s borders and angles offer further attachment sites for muscles, allowing a wide range of movement and flexibility, essential for upper body mobility and strength.

1.0Introduction

• The scapula is a flat, triangular-shaped bone. It is located in the upper thoracic region on the dorsal surface of the rib cage.
• The word scapula comes from the Latin word scapulae, which means "shoulder blades". The origin of the word is thought to be related to its spade-like appearance.
• It resides over the posterior surface of ribs two to seven. The scapula, along with the clavicle and the manubrium of the sternum, make up the pectoral (shoulder) girdle which connects the upper limb of the appendicular skeleton to the axial skeleton.
• The scapula is an important bone as each scapula provides a point of attachment for a number of muscles that make up the arm and shoulder. 
• It also articulates with the humerus and clavicle, forming the glenohumeral (shoulder) joint and acromioclavicular joint respectively.
• However, because the medial aspect of the scapula is not directly attached to the axial skeleton, but is rather held in place and connected to the thorax and vertebral column by muscles, the scapula can move freely across the posterior thoracic wall (scapulothoracic joint). This allows the arm to move with the scapula, providing a wide range of movement and mobility for the upper limb compared to the lower limb.

2.0Costal Surface

• The costal (anterior) surface of the scapula faces the ribcage.
• It contains a large concave depression over most of its surface, known as the subscapular fossa. Originating from the superolateral surface of the costal scapula is the coracoid process. It is a hook-like projection, which lies just underneath the clavicle.
• Glenoid fossa – a shallow cavity, located superiorly on the lateral border. It articulates with the head of the humerus to form the glenohumeral (shoulder) joint.
• Acromion is a triangular process that extends laterally from the spine of the scapula.

3.0 Lateral Surface

• The lateral surface of the scapula faces the humerus. 
• Supraglenoid tubercle – a roughening immediately superior to the glenoid fossa. 
• Infraglenoid tubercle – a roughening immediately inferior to the glenoid fossa.

4.0Posterior Surface

• The posterior surface of the scapula faces outwards. It is marked by:
• Spine – the most prominent feature of the posterior scapula. It runs transversely across the scapula, dividing the surface into two.
• Infraspinous fossa – the area below the spine of the scapula, displays a convex shape. 
• Supraspinous fossa – the area above the spine of the scapula, it is much smaller than the infraspinous fossa
• Acromion – projection of the spine that arches over the glenohumeral joint and articulates with the clavicle at the acromioclavicular joint.

5.0Articulations

The scapula has two main articulations:

• Glenohumeral joint – between the glenoid fossa of the scapula and the head of the humerus.
• Acromioclavicular joint – between the acromion of the scapula and the clavicle.

6.0The Shoulder Joint

• The shoulder joint (glenohumeral joint) is an articulation between the scapula and the humerus.
• It is a ball and socket-type synovial joint, and one of the most mobile joints in the human body.
• The shoulder joint is formed by an articulation between the head of the humerus and the glenoid cavity (or fossa) of the scapula. This gives rise to the alternate name for the shoulder joint – the glenohumeral joint.
• Like most synovial joints, the articulating surfaces are covered with hyaline cartilage.
• The head of the humerus is much larger than the glenoid fossa, giving the joint a wide range of movement at the cost of instability.

7.0Ligaments

• Ligaments play an important role in stabilising the shoulder joint:
• Glenohumeral ligaments (superior, middle and inferior) – extend from the humerus to the glenoid fossa, reinforcing the joint capsule.
• Coracohumeral ligament – extends from the base of the coracoid process to the greater tubercle of the humerus.
• Coracoacromial ligament – extends between the acromion and coracoid process of the scapula, forming an arch-like structure over the shoulder joint (coracoacromial arch). 

8.0Sample Question on Parts of Scapula

Q.1 Label  main parts of scapula diagrametically.