ANATOMY

The principle anatomical components are the wrist and digit extensors.
Most posteriorly is extensor carpii ulnaris and most anteriorly is extensor carpii radialis (Longus and Brevis).
In between is extensor digiti minimi and extensor digitorum.
The most anterior muscle bulk is brachioradialis
Radial nerve lies deep to brachioradialis
The PIN passes between the two heads of supinator

The lateral ligament complex of the elbow comprises three ligaments:
the radial collateral ligament,
the annular ligament,
and the lateral ulnar collateral ligament (LUCL).

The radial collateral ligament lies deep to the common extensor origin.
On most MRI and ultrasound images it can be identified as a separate structure with more densely packed fibres.
If not, the ligament can be assumed to comprise the deepest fibres of the common extensor origin.
Another localising feature is that the meniscal homologue on meniscal flange is attached to it on its deep surface.

The distal end of the radial collateral ligament is attached to the annular ligament.
This ligament runs circumferentially around the radio head attached anteriorly and posteriorly to the ulna.
It is not often injured in adults however in children it can sublux over the radial head allowing subluxation of the head itself.
This is often called "pulled elbow".
Diagnosis is usually made clinically and on plane radiographs and ultrasound or MRI are rarely if ever needed.

The lateral under collateral ligament shares a proximal origin with the radial collateral ligament but then it passes more posteriorly and distally to insert on the ulna.
Part of its function is to prevent posterior subluxation of the radial head.
It is most often injured would contact sports in association with tears of the radial collateral ligament itself
The important anatomical structures in the medial aspect of the elbow include the four flexors, pronator teres and brachialis.
Beginning from posterior, flexor digitorum profundus and flexor digitorum superficialis are separated by flexor carpii ulnaris.
Flexor carpii ulnaris has two heads arising either side of the ulnar groove.
Flexor digitorum superficialis (FDS) separates flexor carpii ulnaris (FCU) from the flexor carpii radialis (FCR).
The principle muscle bulk anteromedially is from pronator teres and the adjacent brachialis.
The principle nerve on the medial side is the ulnar nerve.