Clavicle, scapula and humerus

The **scapula** (plural: **scapulae**) is a roughly triangular shaped bone with several projections connecting the humerus to the clavicle.

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

* coracoid process: 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
* acromion: acromial part of deltoid muscle, trapezius
* scapular spine: spinous part of deltoid muscle, trapezius
* 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, latissimus dorsi (small slip)
* 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 a site of arterial anastomosis between many arteries. This aims to ensure an adequate supply of blood to the upper limb, but has added benefit of adequate supply to the bone itself.

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

Variant anatomy

* The scapular foramen: notch is frequently bridged by bone rather than a ligament (5% of cases studied), converting it into a foramen

* Accessory notches/facets may be present; one frequently is found on the inferior angle.
* The acromion may fail to unite. In about 5% of individuals (more

commonly males), the separate part (os acromion) is on the right side.

* Fascicles of the subclavius muscle may be inserted onto the coracoid process by passing through the clavipectoral fascia.
* The tendon of m. pectoralis minor, in part (15%) or entirely (1%), may pass over the coracoid process to insert elsewhere.
* The coracoid process may exist as a separate bone.
* Os acromionale

The**clavicle** (or informally **collar bone**) is the only long bone that lies horizontally in human skeleton.

Osteology

The clavicle is roughly "S-shaped" with a flattened, concave, lateral one-third and a thickened, convex, medial two-thirds. One the inferior surface of lateral third is the conoid tubercle for the attachment of the conoid ligament and lateral to this is the trapzeoid line for attachment of the trapezoid ligament. On the inferior surface of the medial clavicle is the costal tuberosity and groove for subclavius for the attachment of sternocostal ligament and subclavius muscle respectively.

The female clavicle is shorter, thinner and less curved than the male clavicle.

Articulations

The clavicle articulates with acromion at the acromioclavicular joint laterally and thesternum at the sternoclavicular joint medially.

Attachments

* muscles: pectoralis major, sternocleidomastoid (clavicular head), deltoid,trapezius, subclavius
* ligamentous: acromioclavicular ligament, coracoclavicular ligament, sternoclavicular ligaments

Ossification

It is the first bone to start ossification at around 5th-6th weeks of gestation but finishes around 21-25 years of age. The lateral end has intramembranous ossification. See main article: ossification centres of the pectoral girdle.

Variant anatomy

* supraclavicular foramen: the clavicle may be pierced by a branch of supraclavicular nerve

* coracoclavicular joint- diarthrosis or a cartilaginous symphysis.

* deltoid tubercle - rough area superior of deltoid.
* Bifurcate clavicle and duplication of the clavicle have been described.
* The partial or complete absence of a clavicle