THE HUMERUS

 The Humerus

The humerus is a long bone of the upper limb, which extends from the shoulder to the elbow.

The proximal aspect of the humerus articulates with the glenoid fossa of the scapula, forming the glenohumeral joint. Distally, at the elbow joint, the humerus articulates with the head of the radius and trochlear notch of the ulna.



Proximal Landmarks

The proximal humerus is marked by a head, anatomical neck, surgical neck, greater and lesser tuberosity and intertubercular sulcus.

The upper end of the humerus consists of the head. This faces medially, upwards and backwards and is separated from the greater and lesser tuberosities by the anatomical neck.

The greater tuberosity is located laterally on the humerus and has anterior and posterior surfaces. It serves as an attachment site for three of the rotator cuff muscles – supraspinatus, infraspinatus and teres minor – they attach to superior, middle and inferior facets (respectively) on the greater tuberosity.

The lesser tuberosity is much smaller, and more medially located on the bone. It only has an anterior surface. It provides attachment for the last rotator cuff muscle – the subscapularis.

Separating the two tuberosities is a deep groove, known as the intertubercular sulcus. The tendon of the long head of the biceps brachii emerges from the shoulder joint and runs through this groove.

The edges of the intertubercular sulcus are known as lips. Pectoralis major, teres major and latissimus dorsi insert on the lips of the intertubercular sulcus. This can be remembered with the mnemonic “a lady between two majors”, with latissimus dorsi attaching between teres major on the medial lip and pectoralis major laterally.

The surgical neck extends from just distal to the tuberosities to the shaft of the humerus. The axillary nerve and circumflex humeral vessels lie against the bone here

Shaft

The shaft of the humerus is the site of attachment for various muscles. Cross section views reveal it to be circular proximally and flattened distally.

On the lateral side of the humeral shaft is a roughened surface where the deltoid muscle attaches. This is known is as the deltoid tuberosity.

The radial (or spiral) groove is a shallow depression that runs diagonally down the posterior surface of the humerus, parallel to the deltoid tuberosity. The radial nerve and profunda brachii artery lie in this groove. The following muscles attach to the humerus along its shaft:

1. Anteriorly – coracobrachialis, deltoid, brachialis, brachioradialis.

2. Posteriorly – medial and lateral heads of the triceps (the spiral groove demarcates their respective origins).

Distal Region

The lateral and medial borders of the distal humerus form medial and lateral supraepicondylar ridges. The lateral supraepicondylar ridge is more roughened, providing the site of common origin of the forearm extensor muscles.

Immediately distal to the supraepicondylar ridges are extracapsular projections of bone, the lateral and medial epicondyles. Both can be palpated at the elbow. The medial is the larger of the two and extends more distally. The ulnar nerve passes in a groove on the posterior aspect of the medial epicondyle where it is palpable.

Distally, the trochlea is located medially, and extends onto the posterior aspect of the bone. Lateral to the trochlea is the capitulum, which articulates with the radius.

Also located on the distal portion of the humerus are three depressions, known as the coronoid, radial and olecranon fossae. They accommodate the forearm bones during flexion or extension at the elbow.

Articulations

The proximal region of the humerus articulates with the glenoid fossa of the scapula to form the glenohumeral joint (shoulder joint).

Distally, at the elbow joint, the capitulum of the humerus articulates with the head of the radius and the trochlea of the humerus articulates with the trochlear notch of the ulna.


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