Common extensor origin of the elbow

The common extensor origin of the elbow classically refers to the common tendon of the following forearm extensor muscles, which form a common footprint at the lateral epicondyle ^1,2:

• extensor carpi radialis brevis (ECRB)

• extensor digitorum communis (EDC)

• extensor digiti minimi (EDM)

• extensor carpi ulnaris (ECU)

Gross anatomy

The common extensor origin is a flat tendinous structure originating from the anterolateral surface of the lateral epicondyle and is found just distal to the origin of extensor carpi radialis longus muscle (ECRL) ^1-3. 

The muscle bellies of the extensor digiti minimi and extensor digitorum muscles have been described to blend in the distal third of the forearm. The mere origin of the extensor carpi radialis brevis and extensor digitorum communis tendons are also coalescent but with distinctive tendons and the extensor carpi radialis being more anterior ^2-4. The extensor carpi ulnaris origin on the other hand can be separated with a thick fascia arising posteroinferiorly from the lateral epicondyle of the humerus superficial to the lateral ulnar collateral ligament ^2-4.

Function

The common extensor origin functions as a dynamic stabilizer of the elbow joint and as a secondary restraint to varus force ⁵.

Attachments

Tendinous portions originating from the common extensor footprint distal to the extensor carpi radialis longus origin from anterior to posterior ^2,3: 

• extensor carpi radialis brevis: superficial to the radial collateral ligament

• extensor digitorum communis/extensor digiti minimi

• extensor carpi ulnaris: superficial to the lateral ulnar collateral ligament

Relations

The origin of the extensor carpi ulnaris muscle is found just proximal to the common extensor origin at the lower third of the supracondylar ridge and the humeral attachment of the anconeus muscle is found posteriorly ^1,2.

The common tensor origin is superficial to the lateral collateral ligament complex of the elbow ¹.

Radiographic features

Ultrasound

The common extensor origin is best assessed in longitudinal planes and is characterized by a beak-shaped hyperechogenic appearance. It can be found between the subcutaneous tissue and the lateral epicondyle and/or radial collateral ligament ¹. The tendinous portions of the individual extensor muscles cannot be separated on ultrasound ¹.

MRI

The common extensor origin can be identified as a beak-like tendinous structure superficial to humeral attachment of the radial collateral and lateral ulnar collateral ligaments.

Related pathology

Pathologies associated with the common extensor origin include the following ¹: 

• common extensor tendon injury

• tennis elbow

• elbow instability