The scapula also known as the shoulder blade is a triangular, flat bone of shoulder girdle that articulates with the head of humerus humerus at the glenohumeral joint which is poulalry called as shoulder joint, and with the lateral end of clavicle at the acromioclavicular joint. In doing so, the scapula connects the upper limb to the trunk.
Scapula has got two surfaces, three borders, three angles and three processes. Scapula serves as a site for attachment for many important muscle around shoulder.
- The costal surface ( that abuts thorax) 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 as a lever for the action of the serratus anterior in overhead abduction of the arm.
- The dorsal ( that can be palpated from back) 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.
- The superior border is thin and short. Near the root of the coracoids process it presents the suprascapular notch.
- The lateral border is thick. At the upper end it presents the infraglenoid tubercle.
- The medial border is thin. It extends from the superior angle to the inferior angle.
- The superior angle is covered by the trapezius.
- The inferior angle is covered by the latissimus dorsi. It moves forward round the chest when the arm is abducted.
- The lateral (or glenoid) angle is broad and bears the glenoid cavity (or fossa) which is directed forwards, laterally and slightly upwards.
- The spine (or spinous process) is triangular plate of bone with three borders and 2 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.
- The acromion has two borders, medial and lateral; two surfaces, superior and inferior, and a facet for the clavicle.
- The coracoids process is directed forwards and slightly laterally.
Determination of the side
- The lateral (glenoid) angle is large and bears the glenoid cavity.
- The dorsal surface is convex and is divided by the triangular spine into the supraspinous and infraspinous fossae. The costal surface is concave to fit on the convex chest wall.
- The lateral thickest border runs from teh glenoid cavity above to the inferior angle below.
Scapula is usually fractured in trauma around shoulder. Usually it responds very well to conservative mode of treatments.
Various muscles and ligaments attach on scapula that are used to stabilize and move the bone. Movement of scapula helps in movements of shoulder joint.
- The subscapularis arises from the medial two thirds of the subscapular fossa.
- The serratus anterior is inserted along the medial border of the costal surface-one digitations to the superior angle, two digitations to the medial border, and five digitations to the inferior angle.
- The supraspinatus arises from the medial two thirds of the supraspinous fossa (including the upper surface of the spine).
- The infraspinatus arises from the medial two thirds of the infraspinous fossa (including the lower surface of the spine).
- The deltoid arises from the lower border of the crest of the spine and from the lateral border of the acromion.
- The trapezius is inserted into the upper border of the crest of the spine and into the medial border of the acromion.
- The long head of the biceps arises from the supraglenoid tubercle; and the short head from the lateral part of the tip of the coracoid process.
- The coracobrachialis arises from the medial part of the tip of the coracoid process.
- The pectoralis minor is inserted into the medial border and superior surface of the coracoid process.
- The long head of the triceps arises from the infraglenoid tubercle.
- The teres minor arises from the upper two thirds of the rough strip on the dorsal surface along the lateral border.
- The teres major arises from the lower one third of the rough strip on the lateral aspect of the lateral border.
- The levator scapulae is inserted along the dorsal aspect of the media border, from the superior angle up to the root of the spine.
- The rhomboideus minor is inserted into the medial border (dorsal aspect) opposite the root of the spine.
- The rhomboideus major is inserted into the medial border (dorsal aspect) between the root of the spine and the inferior angle.
- The inferior belly of the omohyoid arises from the upper border near the suprascapular notch.
- The margin of the glenoid cavity gives attachment to the capsule of the shoulder joint and to the glenoid labrum.
- The margin of the facet on the medial aspect of the acromion gives attachment to the capsule of the acromioclavicular joint.
- The coracoacromial ligament is attached
- To the lateral border of the coracoid process, and
- To the medial side of the tip of the acromion process.
- The coracohumeral ligament is attached to the root of the coracoid process.
- The coracoclavicular ligament is attached to the coracoid process: the trapezoid part on the superior aspect, and the conoid part near the root.
- The suprascapular ligament bridges across the suprascapular notch and converts it into a foramen which transmits the suprascapular nerve. The suprascapular vessels lie above the ligament.
- The spinoglenoid ligament bridges the spino-glenoid notch. The suprascapular vessels and nerve pass deep to it.
- Paralysis of the serratus anterior cause ‘winging’ of the scapula. The medial border of the bone becomes unduly prominent, and the arm cannot be abducted.
- In a developmental anomaly called scaphoid scapula, the medial border is concave.
Text adapted from: Human Anatomy by BD Chaurasia
Image Credit: Wikipedia
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