In addition, the external surface of the joint capsule is reinforced laterally where it cuffs the head of the radius with a strong anular ligament of the radius. Although this ligament blends with the fibrous membrane of the joint capsule in most regions, they are separate posteriorly. The anular ligament of the radius also blends with the radial collateral ligament.
The anular ligament of the radius and related joint capsule allow the radial head to slide against the radial notch of the ulna and pivot on the capitulum during pronation and supination of the forearm.
The deep surface of the fibrous membrane of the joint capsule and the related anular ligament of the radius that articulate with the sides of the radial head are lined by cartilage. A pocket of synovial membrane (sacciform recess) protrudes from the inferior free margin of the joint capsule and facilitates rotation of the radial head during pronation and supination.
Vascular supply to the elbow joint is through an anastomotic network of vessels derived from collateral and recurrent branches of the brachial, profunda brachii, radial, and ulnar arteries.
The elbow joint is innervated predominantly by branches of the radial and musculocutaneous nerves, but there may be some innervation by branches of the ulnar and median nerves.
The cubital fossa is an important area of transition between the arm and the forearm. It is located anterior to the elbow joint and is a triangular depression formed between two forearm muscles: the brachioradialis muscle originating from the lateral supra-epicondylar ridge of the humerus, and the pronator teres muscle originating from the medial epicondyle of the humerus (Fig. 7.77A).
The base of the triangle is an imaginary horizontal line between the medial and lateral epicondyles. The bed or floor of the fossa is formed mainly by the brachialis muscle.
The major contents of the cubital fossa, from lateral to medial, are: the tendon of the biceps brachii muscle, the brachial artery, and the median nerve (Fig. 7.77B).
The brachial artery normally bifurcates into the radial and ulnar arteries in the apex of the fossa (Fig. 7.77B), although this bifurcation may occur much higher in the arm, even in the axilla. When taking a blood pressure reading from a patient, the clinician places the stethoscope over the brachial artery in the cubital fossa.
The median nerve lies immediately medial to the brachial artery and leaves the fossa by passing between the ulnar and humeral heads of the pronator teres muscle (Fig. 7.77C).
The brachial artery and the median nerve are covered and protected anteriorly in the distal part of the cubital fossa by the bicipital aponeurosis (Fig. 7.77B). This flat connective tissue membrane passes between the medial side of the tendon of the biceps brachii muscle and deep fascia of the forearm. The sharp medial margin of the bicipital aponeurosis can often be felt.
The radial nerve lies just under the lip of the brachioradialis muscle, which forms the lateral margin of the fossa (Fig. 7.77C). In this position, the radial nerve divides into superficial and deep branches:
The superficial branch continues into the forearm just deep to the brachioradialis muscle.
The deep branch passes between the two heads of the supinator muscle (see pp. 778–780 and Fig. 7.92) to access the posterior compartment of the forearm.
The ulnar nerve does not pass through the cubital fossa. Instead, it passes posterior to the medial epicondyle.