The Elbow Joint

The elbow is the joint connecting the proper arm to the forearm. It is marked on the upper limb by the medial and lateral epicondyles, and the olecranon process. Structually, the joint is classed as a synovial joint, and functionally as a hinge joint.

In this article, we shall look at the anatomy of the elbow joint; its articulating surfaces, movements, stability, and the clinical relevance.


Articulating Surfaces

It consists of two separate articulations:

  • Trochlear notch of the ulna and the trochlea of the humerus
  • Head of the radius and the capitulum of the humerus

(nb: The proximal radioulnar joint is found within same joint capsule of the elbow, but most literature considers it as a separate articulation)

Fig 1.0 - Anterior and posterior views of the articulations of the elbow joint

Fig 1.0 – Anterior and posterior views of the articulations of the elbow joint


Movements of the Joint

The orientation of the bones forming the elbow joint produces a hinge type synovial joint, which allows for extension and flexion of the forearm:

Extension: Triceps brachii and anconeus

Flexion: Brachialis, biceps brachii, brachioradialis


Stability of the Joint

Like all synovial joints, the elbow joint has a capsule enclosing the joint. This in itself is strong and fibrous, strengthening the joint. The joint capsule is thickened medially and laterally to form collateral ligaments, which stablise the flexing and extending motion of the arm.

The radial collateral ligament is found on the lateral side of the joint, extending from the lateral epicondyle, and blending with the anular ligament of the radius (a ligament from the proximal radioulnar joint). 

The ulnar collateral ligament originates from the medial epicondyle, and attaches to the coronoid process and olecrannon of the ulna.

Fig 1.1 - The medial and lateral views of the elbow joint.

Fig 1.1 – The medial and lateral views of the elbow joint.


Bursae

There are many bursae in the elbow, but only a few have clinical important. A bursa (plural bursae) is simply a membranous sac, filled with synovial fluid. It acts to cushion the moving parts of a joint, preventing degenerative damage.

Important bursae:

Intratendinosus: Formed within the tendon of the triceps brachii.
Subtendinosus: Found between the olecrannon and the tendon of the triceps brachii, reducing friction between the two structures during extension and flexion of the arm.
Subcutaneous: Found between the olecrannon and the overlying connective tissue.

Bursae are clinically important, as they can become irritated and inflamed, producing pain.

Clinical Relevance: Injuries to the Elbow Joint

Bursitis

Subcutaneous bursitis:  Repeated friction and pressure on the bursa can cause it become inflamed. Because this bursa lies relatively superficially, it can also become infected (e.g cut from a fall on the elbow), and this would also cause inflammation

Subtendinosus bursitis: This is caused by repeated flexion and extension of the forearm, commonly seen in assembly line workers.  Usually flexion is more painful as more pressure is put on the bursa.

Fig 1.2 - X-ray of a posterior dislocation of the elbow.

Fig 1.2 – X-ray of a posterior dislocation of the elbow.

Dislocation

An elbow dislocation usually occurs when a young child falls on a hand with the elbow flexed. The distal end of the humerus is driven through the weakest part of the joint capsule, which is the anterior side. The ulnar collateral ligament is usually torn and there can also be ulnar nerve involvement

Most elbow dislocations are posterior, and it is important to note that elbow dislocations are named by the position of the ulna and radius, not the humerus.

Epicondylitis (Tennis elbow or Golfer’s Elbow)

Most of the flexor and extensor muscles in the forearm have a common tendonous origin. The flexor muscles originate from the medial epicondyle, and the extensor muscles from the lateral. Sportspersons can develop an overuse strain of the common tendon – which results in pain and inflammation around the area of the affected epicondyle.

Typically, tennis players experience pain in the lateral epicondyle from the common extensor origin. Golfers experience pain in the medial epicondyle from the common flexor origin.

Supraepicondylar Fracture

A supraepicondylar fracture occurs by falling on a flexed elbow. It is a transverse fracture, spanning between the two epicondyles.

Direct damage, or swelling can cause the interference to the blood supply of the forearm via the brachial artery. The resulting ischaemia can cause Volkmann’s ischaemic contracture  – uncontrolled flexion of the hand, as flexors muscles become fibrotic and short. There also can be damage to  the medial, ulnar or radial nerves.

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