Elbow joint

The **elbow** is a complex synovial joint formed by the articulations of the humerus, the radius and the ulna.

The elbow joint is made up of three articulations

* **radiohumeral:**capitellum of the humerus with the radial head
* **ulnohumeral:** trochlea of the humerus with the trochlear notch (with separate olecranon and coronoid process articular facets) of the ulna
* **radioulnar:** radial head with the radial notch of the ulna (proximal radioulnar joint)

In full flexion, the coronoid process is received by the coronoid fossa and the radial head is recevied by the radial fossa on the anterior surface of the humerus and in full extension the olecranon process is received by the olecranon fossa on the posterior aspect of the humerus.

Motion of the elbow joint

* Flexion: ulnohumeral articulation
	+ Brachialis muscle:
	+ Biceps brachii muscle
	+ Brachioradialis muscle
	+ Pronator teres muscle
* Extension: ulnohumeral articulation
	+ Triceps muscle
	+ Anconeus muscle

* Motion of the proximal radio-ulnar joint and radiohumeral articulation
	+ Supination
		- Biceps brachii muscle
		- Supinator muscle
	+ Pronation
		- Pronator teres muscle
		- Pronator quadratus muscle

Ligaments

* medial (ulnar) collateral ligament complex: fan-shaped, extending from medial epicondyle to ulna. It has three components: Anterior band, posterior band, transverse band.
* lateral (radial) collateral ligament complex: originates on lateral epicondyle and distally blends with the anular ligament
* annular ligament: attached to anterior and posterior aspects of radial notch of ulna, forming a collar around the radial head
* quadrate ligament (of Denuce)
	+ thickening of the inferior aspect of the joint capsule
	+ runs from just inferior to the radial notch of the ulna to insert to the medial surface of the radial neck

Joint capsule

The joint capsule encloses all three articulations. It attaches the humerus proximal to the radial, coronoid and olecranon fossae. Distally, it attaches to the annular ligament of the radius and coronoid process of the ulna. The volume of the joint capsule is 24-30 mL.

* Anterior and posterior fat pads are intracapsular but extra-synovial

Fat pads

There are three fat pads of the elbow, which sit between the two layers of the joint capsule, making them extra-synovial.

* coronoid fossa fat pad (anterior)
* radial fossa fat pad (anterior)
* olecranon fossa fat pad (posterior)

Bursae

* Posterior
	+ Subcutaneous olecranon bursa: Located subcutaneously, superficial to olecranon process
	+ Subtendinous olecranon bursa: Located between the triceps tendon and the olecranon
* Anterior
	+ Bicipitoradial bursa: Located between the biceps tendon and the radial tuberosity
* Lateral
	+ Radioulnar bursa: Located between the extensor digitorum and radiohumeral joint

Relations

* anteriorly: biceps brachii tendon; brachialis muscle, median nerve, brachial artery
* posteriorly: olecranon bursae, triceps brachii tendon
* laterally: common extensor tendon; supinator muscle
* medially: ulna nerve

Blood supply

Arterial supply is via anastomotic (medial, lateral and posterior) arcades formed by branches of the radial, ulna and brachial arteries.

Nerve supply

* articular branches of the radial, ulna, median and musculocutaneous nerves

Variant anatomy

* synovial folds
	+ thin projections of synovial membrane (inner layer of joint capsule)
	+ may be confused for intra-articular loose bodies on

MRI

* capitellar and olecranon pseudodefects 6
	+ normal areas devoid of articular cartilage
	+ can be mistaken on MRI for impaction injuries or osteochondral defects
* accessory ossicles
	+ os supratrochlear dorsale
	+ patella cubiti (very rare)

Ossification

* ossifications centers of the elbow (CRITOE) - 1,3,5,7,9,11 year