[Biology Class Notes] on Scapula Pdf for Exam

What is a Scapula?

The flat bone that is in a trilateral shape is known as the Scapula. It is observed positioned at the back of the trunk. The scapula performs a significant role in supporting the other bones connected to the shoulder motion rhythm. The blood supply to the scapula is usually impaired in neurological conditions such as strokes, cerebrovascular accidents, and other brain hemorrhages.   

In the pectoral girdle, a pair of scapula bones are present. It forms the posterior part of the shoulder girdle and is situated over the ribs posteriorly, covering the second to seventh ribs. 

The scapula location is on the outer edge of your ribcage, between ribs 2 and 7. It’s one of the bones that make up the pectoral girdle, including the clavicle or collarbone. The Scapula structure consists of a spine, a coracoid, an acromion process, and a glenoid cavity. 

Scapula Function 

The Scapula is liable for various motions essential to everyday movement and sleek upper extremity motion. The scapula moves forward and back with the pectoral girdle as a result of protraction and retraction. 

Protraction occurs when the whole pectoral girdle moves backwards as the arm is raised from below shoulder level, while retraction occurs as the arm descends from above shoulder level. It supports the shoulder capsule throughout extreme arm movement by revolving upwards and downwards. 

The scapula region is on the higher posterior surface of the trunk and is circumscribed by the muscles that connect to the Scapula (shoulder blade). These scapula muscles can be divided into : 

• Extrinsic scapula muscles – It joins the appendicular skeleton to the axial ( levator scapulae, latissimus dorsi, trapezius, rhomboid minor, and rhomboid major)

• Intrinsic scapula muscles – These muscles join the Scapula to the humerus (deltoid, supraspinatus, infraspinatus, teres minor, teres major, and subscapularis). 

• Stabilization and Rotation of the Scapula – This consists of the serratus anterior, trapezius, levator scapulae, and rhomboid muscles and is attached to the superior, medial and inferior borders of the Scapula.

Scapula Bone Anatomy – Parts of Scapula

Borders

• Superior border: It is the thinnest and the shortest border.

• Medial border: It is a tiny border moving parallel to the vertebral column and is usually ascribed to as the vertebral border.

• Lateral border: It is alternatively identified as the axillary border, operating towards the axilla apex. Among the 3 borders, it is the strongest and the thickest. It also sustains the glenoid cavity, which connects with the rounded head of the humerus, creating the shoulder joint or glenohumeral joint.

Angles

• The superior border meets with the lateral border, creating the lateral angle. 

• The superior border also coincides with the medial border to create the superior angle. 

• The third angle, named the inferior angle, is developed where the lateral and medial borders meet.

Scapula Surfaces

1. Costal Surface – It is the anterior surface of the Scapula covering the thoracic cage or ribcage. It has a large depression oriented toward the back, called the subscapular fossa, from which the subscapularis muscle emerges. A projection hook-like, termed the coracoid method, starts from the superior border of the head of the Scapula, projecting forward and curving laterally, lying under the clavicle.

2. Lateral Surface – This covering of the Scapula faces the humerus. Its major bony landmarks are:

• Glenoid fossa – It is a shoal pyriform cavity found at the lateral angle of the Scapula. It connects with the rounded head of the humerus, creating the glenohumeral (shoulder) joint.

• Supraglenoid tubercle – A tiny projection on the scapula’s glenoid fossa, at the base of the coracoid process.

• Infraglenoid tubercle – It is a rugged impression located on the side part of the Scapula, directly under the glenoid fossa.

3. Posterior Surface – This Scapula faces outwards. Most of the rotator cuff tissues of the shoulder start from here. Its critical anatomical landmarks are:

• Spine: It is a long, thin piece of bone located on the back of the Scapula. It divides the back of the Scapula into two parts: the supraspinous and infraspinous fossa. The spinoglenoid notch connects the two fossae. This notch, situated next to the spine, is bridged by the spinoglenoid ligament. 

• Supraspinous fossa: It is the area over the spine of the Scapula. It is smooth, concave, and wider at its vertebral than at its humeral point. The supraspinatus muscle begins from the heart of this area. It is smaller than the infraspinous fossa, owning the spinoglenoid fossa on its side. 

• Infraspinous fossa: It is the area under the scapula spine. It is convex and significantly bigger than the preceding one. At its higher part, towards the vertebral margin, it displays a shallow concavity. In the core, it is convex, while near the lateral border, it possesses a deep groove flowing from the upper to the lower part.

• Acromion: It is a big bony projection on the uppermost end of the Scapula. It extends over the shoulder joint, articulating with the clavicle at the acromioclavicular (AC) joint.

Articulations of Scapula 

The joint between two bones or cartilages is called articulation. Articulation in the scapula refers to the sliding joint that hosts the head of the humerus and connects the glenoid cavity. The scapula forms important articulations with other bones in the body. It connects to two bones at the top of the arm: the humerus, which leads to the
elbow and the forearm, and the clavicle, or collarbone, which leads to the shoulder.