Discuss the anatomy of the humerus

Definition: the humerus is the bone of the arm. It is the largest bone in the upper limb.
Parts: the humerus is made up of: proximal end, shaft and distal end
(I) proximal end: this consists of the head, anatomical neck, tuberosity and the surgical neck
– head: this forms 1/3 of a sphere and is about 4 times the area of the glenoid cavity of scapula. It faces superiorly; medially and posteriorly. It is covered by hyaline cartilage
– anatomical neck: it is the articular margin of the head. It separates the head from the tuberosities.
– greater tuberosity: it is a bare bone perforated by vessels. It has 3 smooth facets which receive the tendons of the suprapinatus, infrapinatus and teres  minor muscles. It continues downwards as the lateral lip of the bicipita groove (intertubercular groove)
– lesser tuberosity: projects forwards and form the anteromedial side of the head. It has a smooth facet where the tendon of subscapularis attaches. It continues downwards as the medial lip of the bicipital groove
– surgical neck: this joins the proximal end of the humerus to the shaft
(II) shaft: much of this is triangular in shape. The superior end is cylindrical. Anterolaterally there is deltoid tuberosity for the insertion of the deltoid muscle. Inferolaterally on the posterior aspect of the body is the oblique radial groove for the radial nerve.
(III) distal end: it is expanded from side to side and carries the articular surface for the elbow joint. The trochlea fits into the trochlea notch of the ulnar. Proximal to the trochlea are the coronoid and the olecranon fossae. Joining the lateral part of the trochlea is the capitulum. The medial epicondyle projects from the trochlea and the lateral epicondyle projects from the capitulum.
Ossification: primary ossification centre appears in the centre of the shaft at eight week in utero. Upper and lower ends are cartilaginous at birth. Secondary centres appear at both ends as follows:
– Proximal end:
Head…………………………..1st year
Greater tuberosity……… 3rd year
Lesser tuberosity……….. 5th year
These fuse in the 7th year.
– Distal end:
Capitulum…………….. 2nd year
Medial epicondyle….. 5th year
Trochlea…………………..12th year
Lateral epicondyle……. 13th year
These fuse at about 18years.
Clinical correlates:
1. Fracture of the surgical neck results in the lesion of the axillary nerve
2. Fracture of the shaft results in lesion of radial nerve
3. Fracture of the Medial epicondyle results in lesion of the ulnar nerve