In 1991, O'Driscoll et al 1 published the results of an extensive (27 cases) cadaveric study in which he attempted to divide these variations into four types. It has long been recognised that the substance of the cubital tunnel retinaculum can vary dramatically between individuals. Of these, the cubital tunnel is by far the most common.

There are five principal locations where the ulnar nerve may be compressed around the elbow: Elbow flexion, wrist extension and shoulder abduction increases intraneural pressure by six times. This manoeuvre also narrows the canal by 55%. In addition, the shape of the tunnel changes from an oval to an ellipse with elbow flexion. The unusual anatomy of the cubital tunnel and the well‐recognised increase in intraneural pressure associated with elbow flexion are believed to be key issues in the pathogenesis of cubital tunnel syndrome. Sliding has the greatest role in this process, although the nerve itself can stretch by up to 5 mm. Movement of the elbow therefore requires the nerve to both stretch and slide through the cubital tunnel. Firstly, the ulnar follows a relatively constrained path, and secondly, it lies some distance from the axis of rotation of the elbow joint. This anatomical arrangement has two implications for the nerve. Progressing underneath the septum and adjacent to the triceps muscle, it traverses the cubital tunnel to enter the forearm where it passes between the two heads of the flexor carpi ulnaris muscle. It descends the arm just anterior to the medial intermuscular septum and later pierces this septum in the final third of its length. The ulnar nerve is the terminal branch of the medial cord of the brachial plexus, and contains fibres from the C8 and T1 spinal nerve roots. It contains several structures, the most important of which is the ulnar nerve. 1 In turn, the floor of the tunnel is formed by the capsule and the posterior band of the medial collateral ligament of the elbow joint. The cubital tunnel is formed by the cubital tunnel retinaculum which straddles a gap of about 4 mm between the medial epicondyle and the olecranon. THE ANATOMY OF THE ULNAR NERVE AND THE CUBITAL TUNNEL

Cubital tunnel