The humerus is a bone that connects shoulder and elbow. The humerus is the largest bone in the upper limb and the only bone in the upper arm. Humerus movements participate in many day to day essential activities like throwing, lifting, writing and others which require movements of the shoulder joint.
Proximally, humerus forms part of the shoulder joint whereas distally, the humerus articulates with the radius and ulna to form the elbow joint.
The humerus bone acts as an attachment site for many important muscles and ligaments.
Humerus Bone anatomy
For describing the anatomy of the humerus bone, it is divided in three parts
Proximal End of Humerus
Head is the most proximal region of the bone. Head is almost spherical in shape and flattens a bit where it attaches to the scapula and clavicle.
The head is directed medially, backwards and upwards. It articulates with the glenoid cavity of the scapula to form the shoulder joint. The head forms about one-third of a sphere and is much larger than the glenoid cavity.
The line separating the head from the rest of the upper end is called the anatomical neck.
There are two tubercles present.
The lesser tubercle is an elevation on the anterior aspect of the upper end.
The greater tubercle is an elevation that forms the lateral part of the upper end. Its posterior aspect is marked by three impressions-upper, middle and lower.
Bicipital groove separates the lesser tubercle (medially) from the anterior part of the greater tubercle. The sulcus has medial and lateral lips that represent downward prolongations of the lesser and greater tubercles and serves for the attachment of ligaments and muscles
The line separating the upper end of the humerus from the shaft is called the surgical neck.
Shaft of Humerus
The shaft is rounded in the upper half and triangular in the lower half. It has three borders and three surfaces.
The anterior border is a continuation of the lateral lip of the intertubercular sulcus or bicipital groove. In its middle part, it forms the anterior margin of the deltoid tuberosity. The lower half of the anterior border is smooth and rounded.
Anterolateral surface lies between the anterior and lateral borders. The upper half of this surface is covered by the deltoid. It is marked by a V shaped deltoid tuberosity a little above the middle.
The anteromedial surface lies between the anterior and medial borders. Its upper one third is narrow and forms the floor of the bicipital groove. Near the medial border, at almost middle, a nutrient foramen is seen.
Lower End of Humerus
Below the deltoid tuberosity, the humerus gradually widens, doubling its width as it approaches the elbow.
- The capitellum is rounded projection which articulates with the head of the radius. to form radio-capitellar joint.
- The trochlea is a pulley shaped surface. It articulates with the trochlear notch of the ulna to form elbow joint. The medial edge of the trochlea projects down 6 mm more than the lateral edge. This leads to a carrying angle or the angle by which forearm projects from humeral axis.
The coronoid fossa is a depression just above the anterior aspect of the trochlea. It accommodates the coronoid process of the ulna when the elbow is flexed.
The radial fossa is a depression present just above the anterior aspect of the capitulum. It accommodates the head of the radius when the elbow is flexed.
The olecranon fossa lies just above the posterior aspect of the trochlea. It accommodates the olecranon process of the ulna when the elbow is extended.
Attachments of Humerus
The subscapularis is inserted into the lesser tuberosity.
The greater tuberosity gives attachement to insertion of supraspinatus, infraspinatus andteres minor.
- Supraspinatus -uppermost part
- Infraspinatus – Middle
- Teres minor- lower impression
Intertubercular sulcus also gives attachement to insertion of three muscles. The pectoralis major inserts into lateral lip of the intertubercular sulcus in two layers. The teres major is inserts into the medial lip of the intertubercular sulcus. The latissimus dorsi is inserted into the floor of the intertubercular sulcus.
[The contents of the intertubercular sulcus are the tendon of the long head of the biceps, and its synovial sheath along with the ascending branch of the anterior circumflex humeral artery.]
Anatomical neck provides attachment to the capsular ligament of the shoulder joint except on the medial side. On the medial side, the line of attachment dips down by about a centimeter to include a small area of the shaft within the joint cavity.
An aperture is provided for the tendon of the long head of the biceps leaves the joint cavity
Shaft of Humerus
The deltoid tuberosity provides an insertion to deltoid muscle.
A rough area on the middle of medial border is for insertion of coracobrachialis.
The brachialis arises from the lower halves of the anteromedial and anterolateral surfaces of the shaft extending in part on to the posterior aspect.
Upper upper two thirds of the lateral supracondylar ridge give origin to brachioradialis where as lower one third gives rise to extensor carpi radialis longus.
The common extensor origin on lateral epicondyle provides origin to extensor muscles of forearm.
Posterior surface of lateral epicondyle gives rise to anconeus muscle.
The capsular of the elbow joint is attached to along a line that reaches proximal to the radial and coronoid fossae, anteriorly, and on the posterior side, proximal to the olecranon fossa posteriorly.
Side Determination of Humerus Bone
- The upper end is rounded to form the head. The lower end is expanded from side to side and flattened from before backwards.
- The head is directed medially and backwards.
- The lesser tubercle projects from the front of the upper end and is limited laterally by the intertuberacular sulcus (bicipital groove)
Ossification of Humerus
The humerus is ossified from eight centers, one for each of the following parts of humerus – the body, the head, the greater tubercle, the lesser tubercle, the capitellum, the trochlea, and one for each epicondyle.
There are one primary and seven secondary centres .
The center for the body appears near the middle of the diaphysis in the eighth week of fetal life, and soon extends toward the extremities. This is the primary center.
At birth the humerus is ossified in nearly its whole length, only the extremities remaining cartilaginous.
Upper End of Humerus
The ossification centers appear as follow
- Head of the bone – First year
- Greater tubercle – second year
- Lesser tubercle – Fifth year
Centers for the head and tubercles join by 6 years to form a single large epiphysis. This fuses with the body about the twentieth year.
Lower End of Humerus
The ossification centers for lower end are rembered by CRITOE. That is the order of appearance.
The timeline is as follows
- Capitellum – 1-2 year
- Radius – 3-4year
- Internal or medial epicondyle – 5-6 years
- Trochlea – 8 years
- Olecranon – 9-10 years
- External or lateral epicondyle – 11-12 years
About the sixteenth or seventeenth year, the lateral epicondyle and both portions of the articulating surface, having already joined, unite with the body, and at the eighteenth year the medial epicondyle becomes joined to it.
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