Basic Medical Sciences

The humerus bone is the bone of the arm of human beings. It is the longest bone of the upper limb of human beings. The humerus is classified as a typical long bone with a diaphysis and two metaphyses. Anatomically the humerus consists of a shaft, an upper end and a lower end.

Upper end of the humerus: The upper end of the humerus consists of the following parts;

Head: It is the articular part of the upper end forming the glenohumeral joint (shoulder joint) with the glenoid cavity of the scapula. The head is rounded and forms a big sphere as compared to the glenoid cavity.

Anatomical neck: It is the line separating the head of the humerus from the rest of the upper end.

Lesser tubercle: It is a bony elevation in the form a tubercle present in the anterior aspect of the head of the humerus. It is called lesser tubercle because it is comparatively smaller than the other tubercle present lateral to it that is the greater tubercle.

Greater tubercle: It is also a bony elevation in the form of a tubercle but it is a larger than the lesser tubercle and is directed laterally and posteriorly. The posterior side of the tubercle is marked by three impressions namely upper impression, middle impression and lower impression.

Bicipital groove: It is also known as the inter-tubercular sulcus. It is a sulcus present in between the greater tubercle. The medial border of the bicipital groove is formed by the lateral side of the lesser tubercle and the lateral border by the medial side of the greater tubercle.

Surgical neck: It is the line where the upper end of the humerus joins with the shaft of the humerus. It is the most common site of fracture in humerus.

Shaft of the humerus: The shaft of the humerus is the long part of the bone. It is rounded superiorly and triangular inferiorly. It has three borders and three surfaces.

Borders: The borders are anterior border, lateral border and medial border. The anterior border forms the lateral part of the bicipital groove and continues downward. The medial border forms the medial part of the bicipital groove and continues downward to the medial supracondylar ridge. The lateral border forms the lateral supra condylar ridge in the lower aspect of the bone.

Surfaces: The surfaces are anteromedial surface (lying between the anterior and the medial border) the anterolateral surface (lying between the anterior and lateral border) and the posterior surface (lying between the medial and lateral border).

Lower end of the humerus: The lower end is the widest part of the humerus. It has both articular and non articular surfaces. The articular surfaces include a rounded capitulum which articulates with the radius bone and a pulley shaped trochlea which articulates with the ulna bone.

The non-articular surfaces include the medial epicondyle and the lateral epicondyle both of which are the bony projections on their respective sides. There are three fossae namely the coronoid fossa (where the coronoid process of the ulna is accommodated in flexed condition), radial fossa (where the head of the radius is accommodated in flexed condition) and olecranon fossa on the posterior side (where the olecranon process of the ulna is accommodated in extended condition).