Guyon's canal

Where is it located and how is it formed?

Guyon's canal (canalis ulnaris) is located in the hand at the wrist level. It is formed by the splitting of the fascia propria (fascia propria), which represents the thickened distal part of the antebrachial fascia. This split is formed near the lateral margin of the pisiform bone.

On the ulnar side runs the tendon of the flexor carpi ulnaris (m. flexor carpi ulnaris). It attaches to the pisiform bone, which is a sesamoid bone, and from there tendinous fibers extend further to the 5th metacarpal bone. In the deep layer lies the flexor retinaculum (retinaculum musculorum flexorum) — the thickest and strongest ligament of the hand.

What passes through Guyon's canal?

Inside the canal lies the ulnar neurovascular bundle. Its elements have the following topography:

• Ulnar artery (a. ulnaris) — lies more superficially and laterally.
• Ulnar nerve (n. ulnaris) — is located deeper and medially.

At the wrist level, the ulnar nerve divides into a superficial sensory branch and a deep motor branch.

Clinical significance: entrapment neuropathy

Compression of the ulnar nerve in Guyon's canal leads to tunnel syndrome. This pathology is significantly less common than nerve lesions at the elbow level, and reliable statistics on its prevalence are lacking.

Causes of compression:

• External factors: repeated trauma to the hand when working with tools or cycling due to compression of the canal area by the handlebar.
• Internal factors: space-occupying lesions in the canal area and ganglia.

Symptoms of the lesion:

• Development of a "claw hand" deformity.
• Sensory impairment in the 5th finger and the medial surface of the 4th finger.
• As the disease progresses, weakness appears in the muscles innervated by the ulnar nerve: the 1st dorsal interosseous muscle, the remaining interosseous muscles, and the abductor digiti minimi muscle (m. abductor digiti minimi). Meanwhile, strength in other muscle groups is preserved. In mild severity, muscle weakness is not typical.

Differential diagnosis and ENMG

Clinical tests and instrumental methods are used to diagnose the level of the lesion.

• Sensory assessment: with sensory impairment in the 4th–5th fingers and preserved sensation in the hypothenar area, a possible site of compression is Guyon's canal.
• Hypothenar skin wrinkling test: evaluates the function of the palmaris brevis muscle (m. palmaris brevis).
• Exclusion of MND: if the patient exhibits weakness and atrophy of the ulnar muscle group but no sensory disturbances, this is atypical for neuropathy. In such cases, motor neuron disease (MND) or Hirayama disease must be excluded.
• Electroneuromyography (ENMG): used to identify the type of disorders (axonal or demyelinating), assess the severity of the lesion, and determine the level of the lesion (Guyon's canal, forearm, elbow, or arm). When studying the conduction function of the motor fibers of the ulnar nerve, recording is performed from the abductor digiti minimi muscle (m. abductor digiti minimi).

Class and exam questions

What else to study on this topic

• Ulnar nerve (n. ulnaris)
• Fascia propria of the hand (fascia propria)
• Carpal tunnel (canalis carpi)
• Cubital tunnel syndrome

Other topics in the "Anatomical Structures" section

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