The Neural Tunnels Around the Elbow

The ulnar nerve is derived from the medial cord of the brachial plexus (C7-C8, T1). It passes posteriorly through the medial intermuscular septum 8 cm above the epi-condyle and continues distally along the medial margin of the triceps with the superior ulnar collateral artery. It provides no branches in the arm. The ulnar nerve enters the cubital tunnel (Fig. 1.9) posterior to the medial epi-condyle and grooves the posterior portion of the medial collateral ligament. A few small twigs supply the elbow joint.17 The ulnar nerve supplies motor branches to the heads of the flexor carpi ulnaris muscle, passes between them to supply the ulnar half of the flexor digitorum profundus muscle, and then supplies the hand.

The ulnar nerve may be entrapped at a number of sites at the level of the elbow: the arcade of Struthers, the cubital tunnel, the arcade of Osborne, and the anconeus epitrochlearis. The arcade of Struthers is a band of fas-

Arcade Struthers
A

Brachialis muscle

Radial nerve

Radial recurrent artery

Brachialis muscle

Radial nerve

Radial recurrent artery

Superficial branch of radial nerve

Arcade Struthers

Biceps muscle

Brachial artery

Biceps tendon and aponeurosis

Posterior interosseous nerve

Pronator teres muscle Brachioradialis muscle

FIGURE 1.8. Cubital fossa. (A) The cubital fossa is the triangular space formed by a line joining the medial and lateral epicondyles and the borders of the brachioradialis and pronator teres muscles. (B) The contents include the nerves, arteries, and biceps tendon.

Biceps muscle

Superficial branch of radial nerve

Posterior interosseous nerve

Brachial artery

Biceps tendon and aponeurosis

Pronator teres muscle Brachioradialis muscle

FIGURE 1.8. Cubital fossa. (A) The cubital fossa is the triangular space formed by a line joining the medial and lateral epicondyles and the borders of the brachioradialis and pronator teres muscles. (B) The contents include the nerves, arteries, and biceps tendon.

Cubital Tunnel
FIGURE 1.9. The ulnar nerve passes through the arcade of Struthers, the cubital tunnel, and the arcade of Osborne.

cia extending from the medial intermuscular septum to the medial head of the triceps and is present in 70% of the population.18 The ulnar nerve passes under the arcade and is susceptible to compression. This is especially so after anterior transposition of the nerve when adequate release of the arcade is not performed.18 The cubital tunnel is a fibro-osseous tunnel beneath the cubital retinaculum that bridges the medial epicondyle and the olecranon.18 The boundaries of the cubital tunnel are the ulnar groove of the medial epicondyle anteriorly, the medial collateral ligament laterally, and the cubital retinaculum posteriorly (Fig. 1.10). The sensory and intrinsic motor fibers of the ulnar nerve are superficial and are therefore more predisposed to entrapment neuropathy than the mo-

Radial Nerve Transposition
FIGURE 1.10. The ulnar nerve and its components traverse the cubital tunnel (FCU, flexor carpi ulnaris; FDP, flexor dig-itorum profundus).

tor fibers to the flexor carpi ulnaris and the flexor digi-torum profundus muscles. The cubital retinaculum becomes taut with elbow flexion, thus decreasing the capacity of the cubital tunnel and compressing the ulnar nerve. Absence or redundancy of the cubital retinaculum accounts for developmental subluxation of the ulnar nerve.

The arcade of Osborne, which is present in 77% of individuals, is a thickened band of the aponeurosis between the two heads of the flexor carpi ulnaris.5 It tightens with elbow flexion and can cause nerve compression (see Fig. 1.9). The anconeus epitrochlearis is an anomalous muscle that originates at the medial border of the olecranon and inserts into the medial epicondyle. This muscle also can cause ulnar nerve compression.10

The radial nerve is derived from the posterior cord of the brachial plexus (C5-T1) and courses along the spiral groove to pass through the lateral intermuscular septum 10 cm proximal to the lateral epicondyle. In the anterior compartment, it lies between the brachialis and brachio-radialis muscles, supplying motor branches to each (only the lateral portion of the brachialis). The radial tunnel is approximately 5 cm long and extends from the level of the radiocapitellar joint to the proximal edge of the superficial head of the supinator muscle.19 The brachiora-dialis and extensor carpi radialis longus and brevis form the lateral wall of the radial tunnel. The brachioradialis spirals around and over the nerve from lateral to anterior to form the roof of the tunnel. The anterior capsule of the radiocapitellar joint proximally and the deep head of the supinator distally constitute the floor. The superficial cutaneous branch of the radial nerve exits the tunnel prox-imally, and the posterior interosseous nerve diverges posterolaterally to pass beneath the proximal edge of the superficial head of the supinator muscle.

The arcade of Frohse is the fibrous proximal aspect of the origin of the superficial head of the supinator. It attaches in a semicircular manner from the tip of the lateral epicondyle, and its fibers arch downward 1 cm and gain attachment to the medial aspect of the lateral epi-condyle just lateral to the articular surface of the capitel-lum.14 Spinner reported that the lateral half of the arch is fibrous in all individuals and that the medial half is membranous in 70% and fibrous in 30% of individuals.14 The posterior interosseous nerve passes under this arch and may be compressed when the elbow is in pronation.

The tendinous origin of the extensor carpi radialis brevis has a flat, rigid medial edge that may compress the radial nerve. Anterior to the radial head, transverse fibrous bands cross the radial nerve. At the neck of the radius, a fan of vessels including the recurrent branch of the radial artery and muscular branches to the mobile wad of three muscles cross the posterior interosse-ous nerve. These fibrous bands in front of the radial head and the recurrent branch of the radial artery also can cause radial nerve entrapment.

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