Scapula Bone

The scapula is a flat bone that is in a triangular shape. It is found located at the back of the trunk. Bone is a hard tissue that protects various parts of a body and performs several functions such as, is involved in the production of red and white blood cells, it enables mobility, it helps to store minerals, provide structure and support to the body. 

The bone is a complex internal and external structure that can be found in various shapes and sizes. There are five types of bones they are, long bones, short bones, sesamoid bones, flat bones, and irregular bones. Let us see the scapula diagram along with its anatomy.


Scapula Anatomy

The scapula is also known as the wing bone, shoulder bone, blade bone, or shoulder blade bone. It is the bone that is connected to the clavicle and with the humerus. They are present on either side of the body as a mirror image. In humans, the scapula is a flat bone present on the back of the shoulder girdle of the thoracic cage, they are triangular in shape. It provides attachment to the three groups of muscles that include, extrinsic, intrinsic, and rotating and stabilizing muscles. 

  • The intrinsic muscles include the muscles that are attached to the rotator cuff such as, teres minor, subscapularis, supraspinatus, and infraspinatus. These muscles are found attaching to the surface of the scapula and are necessary for the external and internal rotation of the scapula. 

  • The biceps, triceps, and deltoid muscles are present in extrinsic muscles. These connect the infraglenoid tubercle of the scapula, supraglenoid tubercle of the scapula, and spine of the scapula. Glenohumeral joint functions with the help of these muscles.

  • The third group of muscles consists of the serratus anterior, trapezius, levator scapulae, and rhomboid muscles. These are responsible for the rotation and stabilization of the shoulder scapula. 


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Fig: Scapula labelled diagram


Surfaces of Scapula Parts Anatomy

1. Coastal Surface: It's also known as the ventral surface or subscapular fossa. It is on the front side of the scapula structure, to which the subscapularis muscles are attached. The medial sides, two-thirds of the fossa consist of three longitudinal ridges that are oblique and there is another thick ridge that is present adjoining the lateral border. These ridges attach the tendinous insertions and the fleshy fibres that are present in between the surfaces. The upper part of the fossa is a transverse depression, where the bone is found bent on itself at the right angle. It passes through the centre of the glenoid cavity that produces an angle called the subscapular angle. This structure provides greater strength to the body and it also serves as support to the spine and acromion.

2. Lateral Surface: The lateral surface found in the scapula anatomy, faces the humerus. It is the site of the various attachments and the glenohumeral joint. It includes some of the important bony structures that include:

  • Glenoid Fossa: It is a shallow cavity that is present superiorly on the lateral surface. To form a glenohumeral joint or shoulder joint, it joins with the head of the humerus.

  • Supraglenoid Tubercle: It is found present immediately superior to the glenoid fossa. It is known as the place of attachment to the long head of the brachial of the biceps. 

  • Infraglenoid Tubercle: It is found present immediately inferior to the glenoid fossa. It is known as the place of attachment to the long head of the brachial of the triceps.

3. Posterior Surface: As per the scapula anatomy, the back of the scapula is also known as the dorsal surface or posterior surface. It is unequally subdivided into two parts by the spine of the scapula. The portion that is present above the spine is known as the supraspinous fossa and the portion that is present below the spine is known as the infraspinous fossa. These two fossae are connected to each other with the help of a spinoglenoid notch that is present at the lateral side of the root of the spine. On the outer side of the back of the scapula, a ridge is present at the lower part of the glenoid cavity. The ridge is attached to the fibrous septum this helps to separate the infraspinatus muscle from the muscles of the Teres major and Teres minor. 


Scapula Anatomy Angles

There are three angles found in the scapula bone diagram, 

  • The superior or medial angle of the scapula: It is covered by a trapezius muscle, and it is found formed at the junction of the medial and superior borders of the scapula. At the approximate level of the second thoracic vertebrae, the superior angle is found. This angle is thin, smooth, and rounded, it also provides attachment to the fibres of the levator scapulae muscle. 

  • The inferior angle of the scapula: It is the lowest part of the scapula covered by a muscle called latissimus dorsi muscle. As a union of medial and lateral borders of the scapula, this inferior angle is found present. The surface present at the back provides attachment to the fibres of the latissimus dorsi muscle and to the teres major. The scapular line is the name given to the anatomical plane that is found passing through the inferior angle.

  • The lateral or glenoid angle of the scapula: It is also called the glenoid angle or head of the scapula. It is the thickest part of the scapula. 


Scapula Anatomy Borders

It consists of three borders, that include:

  • Superior Border: It is the thinnest and shortest one found extending from the superior angle to the base of the coracoid process. In animals, it also refers to the cranial border. A semicircular notch or scapular notch is formed by the coracoid process base. Here it is further converted to form a foramen with the help of a superior transverse scapular ligament. The suprascapular nerve is found passing through this. 

  • Axillary Border: It is also known as the lateral border. It is the thickest border of all of them. It begins above the lower margin of the glenoid cavity. There is a rough impression present below this cavity called infraglenoid tuberosity that provides origin to the triceps brachii. 

  • Medial Border: It is also known as the vertebral border or medial margin, it is the longest of all three borders. It is found extending from the superior angle to the inferior angle. It is also referred to as the dorsal border in the case of animals. 


Conclusion

The scapula bone is the most one as it connects most of the muscles at the shoulder region and it is found engaging six types of motion. These include retraction, depression, elevation, upward rotation, protraction, and downward rotation. It consists of three borders and three angles. It helps to protect the arm and neck. 

FAQs (Frequently Asked Questions)

1. What is a Scapula? Mention the Parts of Scapula.

Ans: The scapula is a flat bone that is in a triangular shape. It is commonly known as the shoulder blade and is found located at the back of the trunk.

The main parts include, 

  1. Borders: Superior border, medial border, and axillary border.

  2. Angles: Superior angle or medial angle, inferior angle, and glenoid angle or lateral angle.

  3. Surfaces: Coastal surface, lateral surface, and posterior surface.

  4. Muscles: The coracobrachialis, biceps brachii,  triceps brachii, pectoralis minor, serratus anterior, and the subscapularis.

2. How Many Bones are Present in the Shoulder?

Ans: The scapula is made up of three bones they are, 

  • Shoulder blade or scapula

  • Collarbone or Clavicle 

  • Humerus or arm bone.