JOINTS FORMED BY HUMERUS

At its upper end, it forms joint with the scapula to from the shoulder joint (glenohumeral joint). At its lower end, it forms joint with the two bones of the forearm (radius and ulna) separately to form the elbow joint (radiohumeral joint and humeroulnar joint).

GENERAL BONY FEATURES OF HUMERUS BONE

This bone starting from upwards has an upper end, a shaft and then a lower end.

Upper end has following important features:

• The head. It articulates with the glenoid cavity of the scapula to from the shoulder joint.

• The anatomical neck, which is the line separating the head from the rest of the upper end.

• The lesser tubercle which is an elevation on the anterior aspect of the upper end.

• The greater tubercle which is an elevation on the lateral aspect of the upper end.

• The intertubercular sulcus (bicipital groove), which separates the lesser tubercle from the greater tubercle.

• The surgical neck, which is the narrow line separating the upper end of the humerus from the shaft.

Shaft is the part of the bone present between the upper end and the lower end. In the upper half, it is rounder and in the lower half it is triangular in shape.

It has three borders i.e. anterior border, lateral border (at lower end forms lateral supracondylar ridge) and the medial border (at lower end forms the medial supracondylar ridge).

It has three surfaces i.e. the anterolateral surface (a little above the middle, it is marked by v shaped deltoid tuberosity), the anteromedial surface (its upper part forms the floor of the intertubercular sulcus) and the posterior surface (its upper part has an oblique ridge and middle part has a radial groove)

Lower end is expanded and forms the condyle, which has articular and nonarticular parts. The articular part includes:

• The capitulum. It is present anteriorly and forms joint with the head of the radius bone.

• The trochlea, which is pulley shaped surface. It is present on the anterior side of the bone and extends onto the posterior of the bone. It forms joint with the trochlear notch of the ulna.

The nonarticular part has the following features:

• The medial epicondyle, which is a prominent bony projection. It is subcutaneous and can be easily felt on the medial side of the elbow.

• The lateral epicondyle, which is smaller than the medial epicondyle.

• The lateral and medial supracondylar ridges, which are sharp margins present just above the lower end on lateral and medial sides respectively.

• The coronoid fossa, which is a depression present above the anterior aspect of trochlea.

• The radial fossa, which is a depression on the anterior aspect, just above the capitulum.

• The olecranon fossa, which lies above the posterior aspect of the trochlear fossa.

ATTACHMENTS OF THE HUMERUS BONE

Muscles inserted on humerus are:

• Subscapularis (into the lesser tubercle)

• Supraspinatus , infraspinatus and Teres minor (on the greater tubercle)

• Pectoralis major (into lateral lip of intertubercular sulcus)

• Latissimus dorsi (into the floor of the intertubercular sulcus)

• Teres major  (into the medial lip of the intertubercular sulcus)

• Deltoid (into the deltoid tuberosity)

• Coracobrachialis (on the medial border)

Muscles originating from humerus are:

• Brachialis (from anteromedial and anterolateral surfaces of the shaft)

• Brachioradialis and extensor carpi radialis longus (from the lateral supracondylar ridge)

• Pronator teres (humeral head) (from medial supracondylar ridge

• The superficial flexor muscles of the forearm (make common origin from medial epicondyle)

• The superficial extensor muscles (make common origin from lateral epicondyle)

• Anconeus (from the lateral condyle ‘s posterior surface)

• Lateral head of triceps brachii (from oblique ridge on the upper part of the posterior surface above the radial groove) and medial head (from posterior surface below the radial groove

Other particular features:

The three nerves of the forearm are directly related to the humerus and are located at the following position:

• The axillary nerve, at the surgical neck

• The radial nerve, at the radial groove

• The ulnar nerve, behind the medial epicondyle

The contents of the intertubercular sulcus are:

• The branch of the anterior circumflex humeral artery

• Tendon of the long head of the biceps brachii with its synovial sheath

SOME CLINICAL ASPECTS RELATED TO HUMERUS BONE

Following are the common sites where the fracture of humerus bone occurs:

• The surgical neck (mostly by direct blow or fall on an outstretched hand)

• The shaft

• The supracondylar region (common in young age, mostly by fall on the flexed elbow)

If the fracture occurs at the upper and medial thirds junction then it shows delayed union or non union of the bone because of its poor blood supply at this point.

Due to the fracture of the surgical neck, the axillary nerve present there will also be injured and thus paralysis of the muscles i.e. deltoid and teres minor (supplied by the axillary nerve) takes place. Due to this paralysis, the arm of the injured person will not be abducted and the round contour of the shoulder (formed by deltoid) will also be lost.

Due to the fracture of the shaft, the radial nerve and profunda brachii artery can also be damaged which are present there. In this case, paralysis of the extensor muscles of the wrist takes place (as they are supplied by the radial nerve). This results in a wrist drop (unopposed action of the flexors of wrist muscles takes place)

Due to damage to the medial epicondyle, ulnar nerve may be damaged resulting in a deformity, called the ulnar claw.

http://www.anatomic.us/atlas/latissimus-dorsi-muscle/