Scapula

The scapula (plural: scapulae) is a roughly triangular shaped bone of the pectoral girdle with several articulations connecting to the humerus and clavicle. 

Gross anatomy

Osteology

The main part of the scapula, the body, consists of a somewhat triangular-shaped flat blade, with an inferiorly pointing apex, referred to as the inferior angle as well as lateral and superior angles. The scapula is described as having superior, medial, and lateral borders. 

Posteriorly, the scapula is divided into a supraspinous fossa and infraspinous fossa by the scapular spine. Anteriorly, on the costal surface, is the shallow subscapular fossa. 

Laterally is the glenoid fossa, anteriorly is the coracoid process and superiorly is the acromion that is continuous with the scapular spine and arcs anteriorly over the humeral head. The suprascapular notch lies immediately medial to the base of the coracoid process. The spinoglenoid notch lies posteriorly behind the neck.

Articulations

• acromion: clavicle (forming the acromioclavicular joint)
• glenoid cavity: humeral head (forming the glenohumeral joint)

Attachments

Musculotendinous

• supraspinous fossa: supraspinatus muscle
• infraspinous fossa: infraspinatus muscle, teres minor muscle
• subscapular fossa: subscapularis muscle, serratus anterior
• transverse scapular ligament and adjacent superior border of blade: inferior belly of omohyoid
• acromion: acromial part of deltoid muscle, trapezius
• scapular spine: spinous part of deltoid muscle, trapezius
• coracoid process: coracobrachialis, pectoralis minor, short head of biceps muscle
• lateral border (margo lateralis): teres minor muscle, teres major muscle
• vertebral border (posterior): levator scapulae, rhomboid minor muscle, rhomboid major muscle
• inferior angle: teres major muscle, a small slip of latissimus dorsi
• supraglenoid tubercle: long head of biceps muscle
• infraglenoid tubercle: long head of triceps muscle

Ligamentous

• transverse scapular ligament: crosses suprascapular notch, with the suprascapular nerve below (within the resulting foramen) and the suprascapular vessels above
• coracoacromial ligament
• coracoclavicular ligament
• coracohumeral ligament
• glenohumeral ligaments: upper, middle, and lower bands
• acromioclavicular ligament (weak)

Blood supply

The scapula is surrounded by an arterial anastomosis, the scapular anastomosis which aims to ensure an adequate supply of blood to the upper limb, but has added benefit of adequate supply to the bone itself. It consists of the:

• suprascapular artery
• dorsal scapular artery
• branches of subscapular artery (i.e. circumflex scapular artery)

Variant anatomy

• Sprengel deformity
• os acromiale
• tubercle of Luschka
• unfused coracoid process ⁵

Development

See "ossification centers of the pectoral girdle" for information on the scapular ossification centers.

Related pathology

• scapular fracture
• coracoid process fracture
• Bankart lesion
• acromioclavicular joint injury

Fun fact

17 muscles attach to the scapula (in alphabetic order):

1. biceps brachii (both heads)
2. coracobrachialis
3. deltoid
4. infraspinatus
5. latissimus dorsi
6. levator scapulae
7. omohyoid inferior belly
8. pectoralis minor
9. rhomboid major
10. rhomboid minor
11. serratus anterior
12. subscapularis
13. supraspinatus
14. teres major
15. teres minor
16. trapezius
17. triceps brachii (long head)