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Scapula | Shoulder Blade

Outline
Scapula | Shoulder Blade:
It is a flat triangular bone present on the posterior aspect of thoracic framework (ribcage) from 2nd to 7th vertebra.
Borders:
It has three borders; Vertebral (medial) border, Superior border, and Axillary (lateral) border
Angles:
It has three angles; Medial angle, Lateral angle and Inferior angle
Glenoid fossa:
It is a pear shaped fossa that articulates with humerus to form shoulder joint.
Body of scapula:
It has two surfaces; Costal surface and Dorsal surface.
Dorsal Surface: Contains the spine of scapula. Divided by the spine into suraspinous and infraspinous fossae.
Costal Surface: Forms the subscapular fossa.
Acromion:
A triangular of oblong shaped process that is the continuation of spine of scapula
Coracoid Process:
A hook shaped process that along with acromion protest the shoulder joint.
Nutrient Foramina:
Most commonly found in the infraspinous fossa about an inch below the greater scapula notch.
Ossification:
Begins in a cartilaginous model at the end of 2nd month of fetal life. There are 7 or more centers of ossification.

Introduction:
The scapula, or shoulder blade, is a flat triangular bone. It has two surfaces; costal, and dorsal. The bone overlies the postero-lateral aspect of the thoracic framework, reaching from the second to the seventh Borders and angles
The body of the bone is thin except along its margins and where the spine springs from it. The body has three borders and three angles.

Anatomic position of scapula

Anatomic position of scapula

Borders of scapula:

Vertebral border: Vertebral (medial) border is the longest of the three borders of scapula. It stretches from the medial angle above to the inferior angle below. The vertebral border affords a narrow surface for the insertion of the levator scapulae, rhomboid minor and rhomboid major muscles.

Superior border: The superior border, which is thin and sharp, is the shortest of the three. It runs from the medial angle towards the root of the coracoid process. Before reaching the coracoids process, it is interrupted by scapular notch, which lies very close to the medial side of the base of that process. This notch, which is converted into a foramen by a ligament, or occasionally by a spicule of bone, transmits the suprascapular nerve, whilst the suprascapular artery runs above it. Attached to the superior margin, close to the notch, is the posterior belly of the omohyoid muscle.
Axillary border: The axillary (lateral) border, so called from its relation to the hollow of the axilla (armpit), is much stouter than either of the others. It extends from the lateral angle above to the inferior angle below. The upper inch or so of this border, which lies immediately below the glenoid articular cavity, is rough and tubercular, and affords attachment to the long head of the triceps.

costal surface of scapula

costal surface of scapula

dorsal surface of scapula

dorsal surface of scapula

Angles of scapula:

The medial angle is sharp and more or less rectangular. The inferior angle is blunter and more acute and the lateral angle corresponds to that part of the bone which supports the glenoid cavity and the coracoid process.

Glenoid cavity (fossa):

The glenoid cavity is slightly concave from above downwards and from side to side. The cavity is not very deep and affords attachment to the glenoid labrum, which helps to deepen the socket in which the head of the humerus rests.

Body of the Scapula:

The body of the bone has two surfaces, a dorsal and a costal. The former is divided into two fossae by an outstanding process of triangular form, called the spine of scapula. The attached border of this crosses the dorsal surface of the body obliquely in a direction laterally and slightly upwards. The spine extends from the vertebral border towards the centre of the posterior glenoid edge. Separating the spine of the scapula and the glenoid edge is a notch called the great scapular notch. Within this notch the transverse scapular vessels and the supra-scapular nerve. The spine of scapula divides the dorsal surface into two parts; the upper part is called the supraspinous fossa and the lower part is called the infraspinous fossa. The two fossae are communicated with each other through the greater scapular notch. The dorsal free border of the spine is subcutaneous throughout its entire length. Its upper and lower edges are strongly lipped, and serve for the insertion of the trapezius and for the origin of the deltoid respectively.
The costal aspect of the body is hollow from above downwards and from side to side. It is known as the subscapular fossa. Its medial boundary, which is formed by the anterior lipped edge of the vertebral margin, affords attachment to the fibers of insertion of the serratus anterior muscle along the greater part of its extent. The area of insertion of this muscle is, however, considerably increased over the ventral aspects of the medial and inferior angles respectively. To the floor of the subscapular fossa, the subscapularis muscle is attached. The tendinous intersections of this muscle leave their imprint on this surface of the bone in a series of three or four rough lines which converge towards the neck.

scapula lateral view

scapula lateral view

Acromion:

Acromion is a large, somewhat triangular or oblong process that is a continuation of the spine of scapula. It hooks over anteriorly and articulates with the clavicle to form the acromioclavicular joint.

Coracoid process:

The coracoid process is a small hook-like structure on the lateral edge of the superior anterior portion of the scapula. Pointing laterally forward, it, together with the acromion, serves to stabilize the shoulder joint.

Nutrient Foramina:

Foramina for the passage of nutrient vessels are seen in different parts of the bone; the most constant in position is one which opens into the infraspinous fossa, about an inch or so from the scapular notch. Others are met with on the upper and under surfaces of the spine, on the costal aspect near its deepest part, and also around the glenoid margin.

Ossification of Scapula:

Ossification begins in the body of the cartilaginous scapula about the end of the second month of fetal life. At birth the head, neck, body, spine, and base of the coracoid process are well defined; the vertebral margin, inferior angle, glenoid cavity, acromion, and coracoid process, are still cartilaginous. The centre for the upper and anterior part of the coracoid appears in the first year, and fusion, along an oblique line leading from the upper edge of the glenoid cavity to the conoid tubercle, is complete about the fifteenth year. Up till the age of puberty the acromion remains cartilaginous.