Elbow-joint

From ArticleWorld

The elbow joint is the joint that connects the upper arm and forearm. It is a hinge-type joint that allows for flexion of the forearm, extension of the forearm, and pronation and supination of the forearm. The term, pronation, refers to the ability to turn the palm downward, while the term, supination, refers to the ability to turn the palm upward.

Anatomy

The elbow joint itself is formed by the distal attachment of the humerus in the upper arm to both the radius and the ulna in the forearm. The tip of the elbow joint is formed by the bony process of the proximal ulna called the olecranon process.

The joint is stabilized by an anterior ligament that connects the humerus to proximal aspects of the radius and ulna. The posterior ligament is thin and attaches part of the distal humerus to areas of attachment on both the radius and ulna. On the ulnar side of the joint, the ulnar collateral ligaments support the joint while the radial side of the joint is supported by the radial collateral ligament.

The joint itself relies on a large synovial membrane that allows the bones to roll smoothly against one another. The membrane actually divides and extends between the radius and ulna which sit side by side in the forearm. A connective tissue capsule extends around all bony surfaces that might come into contact with one another and encloses the synovial fluid.

Function

The elbow joint carries insertions for muscles that perform several functions. The biceps muscle and triceps muscle insert just distal to the joint and provide for the elbow joint’s flexion and extension, respectively. A number of forearm muscles insert near the elbow, too. The brachioradialis muscle allows the forearm to supinate. The flexor carpi ulnaris muscle simply flexes the wrist.

On the ulna side are the flexor carpi radialis and the pronator teres major muscle. The later muscle allows the forearm to pronate, or to face palm down. When there is pronation or supination around the elbow joint, the radius and ulna are not in the same alignment with one another.

The antecubital fossa of the elbow joint is the point on the inside of the joint where many of the major arteries, veins and nerves pass to the more distal aspects of the upper extremity. This is why this spot is often chosen as a site for drawing blood. Most people have one or two large veins running just underneath the skin in the antecubital fossa.