SCAPULA: ANATOMY|| FUNCTIONS , ATTACHMENTS ,FEATURES AND CLINICAL ANATOMY

 SCAPULA

     

1. The scapula is also known as the shoulder blade. It articulates with the humerus at the glenohumeral joint, and with the clavicle at the acromioclavicular joint. 

2. The scapula (Latin shoulder blade) is a thin bone placed on the posterolateral aspect of the thoracic cage. The Scapula has two surfaces, three borders, three angles, and three processes 

Side Determination:

1. The lateral or glenoid (Greek socket) 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 Occupied by the concave subscapular fossa to fit on the convex chest wall .

3. The thickest lateral border runs from the glenoiad cavity above to the inferior angle below.

FEATURES:

             

Surface :

1. The costal surface or subscapular fossa 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 asba lever for the action of the serratus anterior in overhead abduction of the arm. 

2. The dorsal 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.

Borders :

1. The Superior border is thin and shorter. Near the root of the coracoid process, it presents the suprascapular notch.

2. The lateral border is thick. At the upper end, it presents the infraglenoid tubercle.

3. The medical border is thin. It extends from the superior angle to the inferior angle. 

 Angles: 

1. The superior angle is covered by the trapezius. 

2. The inferior angle is covered by the latissimus dorsi. It moves forwards 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. 

Processes:

1. The spine or spinous process is a triangular plate of bone with three borders and two 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 coracoid (Greek like a crow's beak) process is directed forwards and slightly laterally. It is bent and finger-like. It is atavistic type of epiphysis.

Attachments :

                  

1. The multipennate Subscapularis arises from the medial two-thirds of the subscapular fossa . 

2. The supraspinatus arises from the medial two-thirds of the supraspinous fossa including the upper surface of the spine. 

3. The infraspinatus arises from the medial two-thirds of the infraspinous fossa, including the lower surface of the spine. 

4. The deltoid arises from the lower border of the crest of the spine and from the lateral border of the acromion.The acromial fibres are multipennate. 

5. The trapezius is inserted into the upper border of the crest of the spine and into the medial border of the acromion. 

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OSSFICATION : 

         

The scapula ossifies from one primary centre and seven secondary sentres. The primary centre appears near the glenoid cavity during the eighth week of development. The first secondary centre appears in the middle of the coracoid process during the first year and fuses by the 15th year. The subcoracoid centre appears in the root of the coracoid process during the 10th year and fuses by the 16th to 18th years. The other centres, including two for the acromion, one for the lower two-thirds of the margin of the glenoid cavity, one for the medial border and one for the inferior angle, appear at puberty and fuse by the 25th year. 

The fact of practical importance is concerned with the acromion. If the two centres appearing for acromion fail to unite, it may be interpreted as a fracture on radiological examination. In such cases, a radiograph of the opposite acromion will mostly reveal similar failure of union.

CLINICAL ANATOMY :

           

⚫ Paralvsis of the serratus anterior causes 'winging' of the scapula, The medial border of the bone becomes unduly prominent, and the arm cannot be abducted beyond 90 degrees 

⚫ The scaphoid scapula is a developmental anomaly in which the medial  border is concave.