Humerus Bone – Upper Arm

Fun Facts about the Humerus

The humerus is the long bone of the upper arm/limb.

Here are three interesting facts about the humerus bone:

1. The humerus is the longest bone in the upper limb. 

2. Located between the shoulder and the elbow, the humerus is responsible for supporting the upper arm and performing daily movements such as eating and carrying objects. 

3. The humerus is often referred to as the “funny bone’. However, the tingling sensation that comes from hitting your humerus is due to compression of the ulnar nerve that curves around the elbow. 

In this article, we will learn in detail the structure and function of this bone, and discuss the consequences of a humerus fracture.

Structure

The humerus consists of three parts; a humeral shaft, upper end, and lower end. The upper end of the bone is round to make the head. On the other hand, the lower end of the humerus is expanded and flattened from side to side.

Anatomical parts of the humerus consist of the head, anatomical/surgical neck, shaft, epicondyles (upper and lower ends), tubercles (greater and lesser for attachment of muscles of the arm), and capitulum (for articulation at the elbow).

Head and upper end

The Head of the humerus is rounded. In the upper end of the bone, there are other structures as the greater tubercle, lesser tubercle, bicipital groove, or intertubercle groove for muscular attachments.

Shaft

The shaft of the humerus is rounded in its upper half and triangular in the lower half. The shaft of the humerus consists of surfaces and borders for muscle and tendon attachments.

Lower end

The lower end of the humerus forms structures known as condyles that expand from one side to the other. The lower end contains a few non-articulating and articulating structures (for forming a joint with the elbow)

Borders of the humerus

To understand the borders of the humerus, you need to understand the definition of a few basic anatomical terms.

• Anterior (or ventral): describes the front or direction towards the front of the body.
• Posterior (or dorsal): this describes the back or direction toward the back of the body.
• Superior (or cranial): a position above or higher than another part of the body.
• Inferior (or caudal): a position below or lower than another part of the body.
• Lateral: describes the side or direction toward the side of the body. Example: The thumb is farther away from the body than the other digits, so it is lateral to the body
• Medial: describes the middle or direction toward the middle of the body. Example: The big toe is closer to the body than the other digits, so it is medial to the body.
• Proximal describes a position in a limb that is nearer to a certain point of attachment on the limb e.g. the elbow.
• Distal describes a position in a limb that is farther from a certain point of attachment.
• Superficial describes a position closer to the surface of the body. E.g. The skin is superficial to the bones.
• Deep describes a position farther from the surface of the body. E.g The brain is deep to the skull.

Medial border

• Its upper part of the medial border forms a groove for muscular attachment.
• The middle portion of the medial border is rough stripped.
• The medial border continues with the medial supracondylar ridge on the lower end of the humerus.

Anterior border

• The upper part of the lateral border forms a groove.
• The middle portion forms a projection of bone known as deltoid tuberosity.
• The lower end of the anterior border is round-shaped and smooth.

Lateral border

• The upper end of the lateral border is not prominent or noticeable.
• The middle portion of the lateral border contains a spinal and radial groove for muscular attachment.
• The lower end of the lateral border forms a lateral supracondylar ridge.

Muscles attachment

Several muscles of the arm, elbow, shoulder, and forearm attach, start or end on the humerus bone, they include :

• Supraspinatus
• Infraspinatus
• Pectoralis major
• Teres major
• Latissimus dorsi
• Deltoid
• Tricep brachii etc

Nerve Supply

The axillary nerve from the brachial plexus wraps around the neck of the humerus. It provides innervation to teres minor, rotator cuff muscles, and deltoid. The radial nerve, which is also one of the five branches of the brachial plexus innervates multiple regions of the forearm, including the heads of the triceps brachii muscle of the upper arm.

Blood Supply

For the upper end of the humerus, the primary blood supply is from posterior and anterior circumflex humeral arteries which are branches of the axillary artery. Profunda brachii artery gives blood supply to the rest of the humerus.

Functions of the humerus

The two integral functions of the humerus in the body are support and movement.

The humerus forms a joint with the shoulder or scapula and an elbow joint with the ulna and radius bones. Several movements occur at the shoulder joint, however just two movements; extension and flexion are possible on the elbow joint.

Possible movements with the humerus and its joints are:

• Circumduction – rotation of the shoulder joint
• Adduction – the movement of the arm towards the body
• Abduction – the movement of the arm away from the body
• Extension of the arm – the movement of the arm behind the torso
• Flexion of the arm – the movement of the arm in front of the torso or overhead
• Extension of the elbow – full opening or stretching of the arm
• Flexion of the elbow – the movement of the forearm towards the body

Clinical Relevance and Associated Diseases

Humerus Fracture

The most common pathology or injury of humerus bone is a fracture. The most common fracture sites for humerus are the:

• Humeral neck
• Shaft of humerus
• Supracondylar region

Fractures at the humeral head are slow to heal due to the insufficient blood supply of the humeral head.

The most common fracture at a young age is a supracondylar fracture. The cause of this fracture is a fall or injury on the outstretched hand. In this fracture, the lower end of the bone tends to displace backward. Thus, it makes the elbow prominent. In this fracture, the most commonly injured nerve is the median nerve.

Dislocations

A dislocation is an injury in which the ends of your bones are forced out from their normal positions in your joints. The common causes include trauma resulting from a fall, an auto accident, or a collision during contact or high-speed sports.

Dislocations are common problems with the shoulder joint. They include:

• Anterior dislocation
• Posterior dislocation
• Inferior dislocation

The most common dislocation for the humerus head is inferior dislocation due to a lack of structural support in the articulating surfaces of the shoulder joint.

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