The Humerus
The humerus is a long bone consisting of three parts; the head which is directed upwards and medially, the shaft, and the lower end. The head, which is shaped like half of a sphere articulates with the glenoid cavity to form the shoulder joint. The anatomical neck surrounds the margins of the head and separates it from the two tuberosities. The lesser tuberosity is a small anterior projection which lies just medial to the bicipital groove. In contrast, the greater tuberosity is a lateral projection from the head, just lateral to the bicipital groove, and carries three impressions; the upper, middle and lower. The intertubercular sulcus (bicipital groove) lies between the greater and lesser tuberosities and has a lateral lip, floor and a medial lip. The area between the upper end and the shaft is called the surgical neck.
Figure1: The humerus
The lower part of the medial border forms the medial supracondylar ridge, while the lateral border extends from the back of the greater tuberosity to form the lateral epicondyle. A rough impression on the middle of the anterolateral surface of the humerus is called the deltoid tuberosity. The spiral groove lies in the middle third of the posterior surface of the humerus.
Figure1: The humerus ( Upper part )
The anterior surface of the lower end contains the trochlea, which is pulley-shaped for articulation with the trochlear notch of the ulna, lateral to the trochlea, a rounded projection called the capitulum for articulation with the head of the radius. The medial epicondyle is a prominent ridge projecting on the medial side of the lower end, which shows a rough impression on its anterior surface and a shallow groove on its posterior surface. The lateral epicondyle is smaller than the medial epicondyle and it shows a rough impression on its anterior surface. The coronoid fossa lies above the trochlea anteriorly and the radial fossa lies above the capitulum anteriorly. On the posterior surface, just above the trochlea lies a larger fossa, called the olecranon fossa.
Figure3: Humerus ( Lower part )
The attachment of muscles
1) To the greater tuberosity three muscles are inserted supraspinatus to the upper part, infraspinatus to the middle part, teres minor to the lower impression, while subscapularis is the only muscle inserted into the lesser tuberosity.
2) Three muscles are inserted into the bicipital groove: pectoralis major into the lateral lip, latissimus dorsi into the floor, and teres major into the medial lip.
3) Two muscles originate from the lateral supracondylar ridge: brachioradialis and extensor carpi radialis longus, and one from the medial supracondylar ridge - pronator teres.
4) A common flexor tendon arises from the medial epicondyle and a common extensor tendon from the lateral epicondyle.
5) Anconeus also arises from the posterior surface of the lateral epicondyle.
6) The medial and lateral heads of triceps originate from the posterior surface of the shaft, the lateral head from the oblique ridge lateral to the spiral groove and the medial head from the posterior surface medial to the spiral groove.
7) Deltoid is inserted in the deltoid tuberosity at the middle of the anterolateral surface of the humerus.
8) Brachialis arises from the lower 1/2 of anterior surface of the humerus.
9) Coracobrachialis is inserted in the impression at the middle of the medial border of the humerus.
2) Three muscles are inserted into the bicipital groove: pectoralis major into the lateral lip, latissimus dorsi into the floor, and teres major into the medial lip.
3) Two muscles originate from the lateral supracondylar ridge: brachioradialis and extensor carpi radialis longus, and one from the medial supracondylar ridge - pronator teres.
4) A common flexor tendon arises from the medial epicondyle and a common extensor tendon from the lateral epicondyle.
5) Anconeus also arises from the posterior surface of the lateral epicondyle.
6) The medial and lateral heads of triceps originate from the posterior surface of the shaft, the lateral head from the oblique ridge lateral to the spiral groove and the medial head from the posterior surface medial to the spiral groove.
7) Deltoid is inserted in the deltoid tuberosity at the middle of the anterolateral surface of the humerus.
8) Brachialis arises from the lower 1/2 of anterior surface of the humerus.
9) Coracobrachialis is inserted in the impression at the middle of the medial border of the humerus.
Figure4: Attachment of the humerus ( upper part)
Figure5: Attachment of the humerus ( lower part )
Structures related to the humerus
Nerves related to the humerus
The axillary nerve is related to the surgical neck of the humerus. The radial nerve runs in the spiral groove, while the ulnar nerve passes behind the medial epicondyle.
The axillary nerve is related to the surgical neck of the humerus. The radial nerve runs in the spiral groove, while the ulnar nerve passes behind the medial epicondyle.
Arteries related to the humerus
The anterior and posterior circumflex humeral artery encircle the surgical neck. An ascending branch arises from the anterior circumflex humeral artery and ascends in the bicipital groove. The profunda brachii artery accompanies the radial nerve in the spiral groove.
The structures pass in the bicipital groove
The tendon of the long head of biceps, and the ascending branch from the anterior circumflex humeral artery pass into the bicipital groove.
