The scapula is also known as the shoulder blade. It articulates with the humerus at the glenohumeral joint, and with the clavicle at the acromioclavicular joint. In doing so, the scapula connects the upper limb to the trunk.
It is a triangular, flat bone, which serves as a site for attachment for many (17!) muscles.
In this article, we shall look at the bony landmarks on the costal, lateral and posterior surfaces of the scapula.
The anterior surface of the scapula is termed ‘costal’, this is because it is the side facing the ribcage.
This side of the scapula is relatively unremarkable, with a concave depression over most of its surface, called the subscapular fossa. The subscapularis muscle, one of the rotator cuff muscles, originates from this side.
Originating from the superolateral surface of the costal scapula is the coracoid process. It is a hook-like projection, which lies just underneath the clavicle. The pectoralis minor attaches here, while the coracobrachialis and biceps brachii muscles originates from this projection.
The lateral surface of the scapula faces the humerus. It is the site of the glenohumeral joint, and of various muscle attachments.
Glenoid fossa – A shallow cavity, which articulates with the humerus to form the glenohumeral joint. The superior part of the lateral border is very important clinically, as it articulates with the humerus to make up the shoulder joint, or glenohumeral joint.
Supraglenoid tubercle – A roughening immediately superior to the glenoid fossa, this is the place of attachment of the long head of the biceps brachii.
Infraglenoid tubercle – A roughening immediately inferior to the glenoid fossa, this is the place of attachment of the long head of the triceps brachii.
The posterior surface of the scapula faces outwards. It is a site of attachment for the majority of the rotator cuff muscles of the shoulder.
Spine – The most prominent feature of the posterior scapula. It runs transversely across the scapula, dividing the surface into two.
Infraspinous fossa – The area below the spine of the scapula, it displays a convex shape. The infraspinatus muscle originates from this area.
Supraspinous fossa – The area above the spine of the scapula, it is much smaller that the infraspinous fossa, and is more convex in shape. The supraspinatus muscle originates from this area.
Acromion – projection of the spine that arches over the glenohumeral joint and articulates with the clavicle.
The glenoid fossa of the scapula articulates with the humerus to form the glenohumeral joint, better known as the shoulder joint. The clavicle and the acromion join to form the acromioclavicular joint, just superior to the shoulder joint.
Fractures of the Scapula
Fractures of the scapula are relatively uncommon, and if they do occur, it is an indication of severe chest trauma. They are frequently seen in high speed road collisions, crushing injuries, or sports injuries.
The fractured scapula does not require much intervention, as the tone of the surrounding muscles holds the pieces in place for healing to occur.
Winging of the Scapula
The serratus anterior muscle originates from ribs 1-8, and attaches the costal face of the scapula, pulling it against the ribcage. The long thoracic nerve innervates the serratus anterior.
If this nerve becomes damaged, the scapula protrudes out of the back when pushing with the arm. The long thoracic nerve can become damaged by trauma to the shoulder, repetitive movements involving the shoulder or by structures becoming inflamed and pressing on the nerve.