Scapula: The scapula is also known as the shoulder blade. It articulates with the humerus at the glenohumeral joint, and the clavicle at the acromioclavicular joint. It is a triangular, flat bone, which attachment for 17 muscles.
Muscles of the Scapula
- Coracobrachialis arises from the medial part of the tip of coracoids process.
- Deltoid arises from the lower border of the crest of the spine and from lateral border acromion.
- Infraspinatus arises from medial 2/3rds of the infraspinous fossa, including lower surface of the spine.
- Inferior belly of omohyoid arises from the upper border near suprascapular notch of the scapula.
- Long head of biceps brachii arises from supraglenoid tubercle and the short head from the lateral part of the tip of coracoids process of the scapula.
- Long head of triceps arises from infraglenoid tubercle.
- Levator scapulae is inserted along the dorsal aspect of the medial border, from the superior angle up to the root of the spine.
- Latissimus Dorsi lower fibers originate from inferior angle of the scapula.
- Pectoralis minor is inserted into the medial border and superior surface of coracoids process of the scapula.
- Rhomboideus minor is inserted into medial border (dorsal aspect) opposite to root of the spine.
- Rhomboideus major is inserted into the medial border (dorsal aspect) between the root of the spine and inferior angle of the scapula.
- Serratus anterior is inserted along the medial border of the costal surface; 1 digitation from the superior angle to the root of the spine, 2 digitations to the medial border, 5 digitations to the inferior angle of the scapula.
- Subscapularis arises from the medial 2/3rds of the subscapular fossa.
Supraspinatus arises from medial 2/3rds of supraspinous fossa including the upper surface of the spine.
- The trapezius is inserted into upper border of the crest of the spine and into medial border of the acromion of the scapula.
- Teres major arises from lower 1/3rd of the rough strip on the dorsal aspect of the lateral border.
- Teres minor arises from upper 2/3rds of the rough strip on the dorsal surface along the lateral border.
Movements of the Scapula
Movements of the scapula are carried by the scapular muscles. The scapula can do six moves:
- Retraction (adduction): rhomboids and middle trapezius muscles
- Protraction (abduction): serratus anterior muscle
- Elevation: upper trapezius and levator scapulae muscles
- Depression: lower trapezius muscle
- Upward rotation: upper and middle trapezius muscle
- Downward rotation: rhomboids muscles
The anterior surface of the scapula is known as the ‘costal’ surface.
This side of the scapula is relatively unremarkable, with a concave depression over most of its surface, called the subscapular fossa. The subscapularis muscle originates from this side.
The lateral surface of the scapula meets the humerus. It is the position of the glenohumeral joint, and of numerous muscle attachments.
Glenoid fossa – A shallow cavity, which connects with the humerus to settle the glenohumeral joint. The superior part of the lateral border is very significant clinically, as it connects with the humerus to make up the shoulder joint.
Supraglenoid tubercle – A roughening immediately above to the glenoid fossa, this place is the attachment of the long head of the biceps brachii.
Infraglenoid tubercle – A roughening immediately under to the glenoid fossa, this place is the attachment of the long head of the triceps brachii.
The posterior surface of the scapula faces outwards. The posterior surface is a site of attachment for the majority of the rotator cuff muscles of the shoulder.
Spine – This most prominent feature of the posterior scapula. It goes transversely beyond the scapula, dividing the surface into two-
Supraspinous fossa – The area above the spine of the scapula, it is much smaller than the infra spinous fossa and is more convex in shape. The supraspinatus muscle originates from this area.
Infraspinous fossa – The area below the spine of the scapula, it displays a convex shape. The infraspinatus muscle originates from this area.
Acromion – ridge of the spine that extends over the glenohumeral joint and connects with the clavicle.
Ligaments & Bursae of the Scapula
Ligaments of the Scapula
- The acromioclavicular ligament attaches the distal end of the clavicle to the acromion of the scapula and provides horizontal stability.
- The coracoacromial ligament is connected to the lateral border of the coracoids process and to the medial side of the tip of the acromion process of the scapula.
- The coracohumeral ligament is connected to the root of the coracoids process of the scapula.
- The coracoclavicular ligament is connected to the coracoid process; the trapezoid part on the superior aspect, and the conoid part near the root of the scapula.
- The coracoclavicular ligament is built up of 2 bands: the conoid and the trapezoid, both of which provide vertical stability. The coracoacromial ligament connects the coracoid process to the acromion of the scapula.
- The margin of the glenoid cavity of the scapula gives adjunct to the capsule of the shoulder joint and to the glenoid labrum.
- The margin of the facet on the medial aspect of the acromion of the scapula gives attachment to the capsule of the acromioclavicular joint.
- The suprascapular ligament links across the suprascapular notch and converts it into a foramen which transmits the suprascapular nerve. The suprascapular ligament lies above the ligament.
- The spinoglenoid ligament links the spinoglenoid notch of the scapula. The suprascapular vessels and nerve passageway to it.
Bursae of the Scapula
There are two significant bursae within the scapula:
Scapulothoracic Bursa, within the serratus and the thorax, moreover
Subscapularis Bursa, within the subscapularis and the serratus.
Ossification of the Scapula
The scapula ossifies from one primary center including seven secondary centers. The primary center develops near the glenoid cavity throughout the 8th week of development. The 1st secondary center develops in the middle of the coracoid process of the scapula throughout the first year and fuses by the 15th year of age. The subcoracoid center develops in the root of the coracoid process throughout the 10th year and fuses by the 16th to 18th years of age. The other centers, including 2 for the acromion, one for the medial border, one for the lower 2/3rds of the margin of the glenoid cavity and one for the inferior angle of the scapula develop at puberty and fuse by the 25th year.
Clinical Significance of the Scapula
Because of its protected location, fractures of the scapula are uncommon. Scapular fractures is an indication of severe chest trauma. Scapular fractures involving the anatomical neck of the scapula and the surgical neck of the scapula.
An abnormally projecting inferior angle of the scapula is identified as a winged scapula and can be produced by paralysis of the serratus anterior muscle. In this situation, the sides of the scapula nearest the spine are located outward and backward. The image of the upper back is assumed to be wing-like.
The scapula performs a significant role in shoulder impingement syndrome.
The abnormal scapular function is called scapular dyskinesis. One action the scapula performs a motion is the elevation of the acromion process in sequence to avoid impingement of the rotator cuff tendons. If the scapula defaults to properly elevate the acromion, shoulder impingement may develop.