Anatomy of the elbow joint

The elbow joint is a hinge type of synovial joint, and it’s actually made up of two separate joints which work together as one.

The first joint, called the humero-ulnar joint, is between the trochlea of the humerus and the trochlear notch of the ulna; and second one, called the humero-radial joint situated between the capitulum of the humerus and the superior aspect of the head of the radius.

A good way to remember this is thinking of the ‘CRAzy TULips’. The CRA in CRAzy represents the Capitulum which articulates with the RAdius, and the TUL in TULips represents the Trochlea which articulates with the ULna.The elbow joint is covered by a synovial membrane, which is surrounded by a joint capsule.

The joint capsule extends from the margins of the articular surfaces of the capitulum and trochlea on the humerus, to the coronoid process anteriorly; and to the olecranon fossa posteriorly.

On both the medial and lateral sides, the elbow joint is strengthened by two strong ligaments called the collateral ligaments which are thickenings of the elbow joint capsule .On the medial side, also called the ulnar side, there’s the ulnar collateral ligament, which extends from the medial epicondyle of the humerus to the coronoid process and the olecranon of the ulna.

The ulnar collateral ligament actually consists of three separate bands: anterior, posterior and oblique. The anterior band is the strongest, and it runs from the medial epicondyle to the tubercle of the coronoid process.

This band helps limit elbow extension. Next, there’s the fan-shaped posterior band, the weakest of all, and it runs from the medial epicondyle to the olecranon of the ulna.

This helps limit elbow flexion. Finally, there is the thin oblique band, which makes the socket for the trochlea slightly deeper, reducing the chance of dislocation.

On the lateral side, there’s the radial collateral ligament, which extends from the lateral epicondyle of the humerus to the annular ligament which it blends with.

The annular ligament encircles the radial head and binds it into the radial notch of the ulna allowing for pronation and supination of the forearm.

Now, the elbow joint is also surrounded by synovial fluid-filled bursae, which are basically pockets of synovial fluid that provide lubrication and reduce the friction when structures such as tendons, skin, muscles and bones rub against each other with movement.

There are three main elbow bursae. First, there’s the subcutaneous olecranon bursa, which lies between the olecranon and the subcutaneous tissue; then, the subtendinous olecranon bursa, situated between the tip of the olecranon and the triceps brachii tendon; and third, there’s the intratendinous olecranon bursa, which lies within the triceps brachii tendon at the point of its insertion onto the olecranon.

Finally, another important bursa, called the bicipitoradial bursa is situated in the cubital fossa which is a small, fat-filled, triangular space on the anterior aspect of the elbow.

Specifically, the bicipitoradial bursa is situated between biceps brachii tendon and the tuberosity of the radius.As a hinge type synovial joint, the elbow can do only two types of movements.

That’s what any hinge does… right? It opens and closes.

The same goes for the elbow. This joint extends and flexes.

Extension is mainly done by the triceps brachii, while flexion is mainly done by the brachialis and the biceps brachii muscles.

The elbow joint receives its blood supply from the elbow’s periarticular anastomosis, formed by the branches of the collateral and recurrent branches of the brachial artery, as well as the profunda brachii, and the radial and ulnar arteries.

Finally, regarding innervation, remember Hilton’s law, which says the nerves that innervate the muscles crossing over a particular joint also innervate that joint.

So according to Hilton’s law, the elbow joint is innervated by three nerves: the musculocutaneous nerve, the radial nerve, and ulnar nerve.

Before we wrap up, feel free to hit the pause button and see if you can remember the bands of the ulnar collateral ligament.

Hint - there are three of them! Alright, as a quick recap.

The elbow joint is a hinge type synovial joint which allows flexion and extension of the elbow. On both the medial and lateral sides, the elbow joint is strengthened by the ulnar and radial collateral ligaments, respectively, which are thickenings of the elbow joint capsule that provide stability to the elbow joint.

There are three main elbow bursae: the subcutaneous olecranon bursa, the subtendinous olecranon bursa, the intratendinous olecranon bursa.

Blood supply for the elbow joint comes from the periarticular anastomosis, while innervation is handled by the musculocutaneous,