Guyon Canal Syndrome
Guyon Canal syndrome also known as Ulnar Tunnel Syndrome is a relatively rare peripheral ulnar neuropathy.
It defined as compression of the distal ulnar nerve at the level of the wrist as it passes Guyon canal. The clinical presentation can be purely sensory, purely motor or both depending on the location of the nerve compression.
Clinically Relevant Anatomy
The ulnar nerve emerges from the medial cord (C8-T1) of the brachial plexus, it travels into the axilla and passes in the anterior compartment of the arm, then it pierces the intramuscular septum and travels in the posterior compartment. It then travels posterior to the medial epicondyle into the cubital fossa. The nerve then passes between the flexor carpi ulnaris and flexor digitorum profundus muscles. The ulnar nerve gives off dorsal cutaneous branch 8.3 cm proximal to the pisifrom bone, before it enters Guyon’s canal.
The Guyon Canal extends between the proximal boarder of the pisiform bone and distally at the hook of the hamate. The ulnar nerve and ulnar artery pass through the Guyon canal as they pass from distal forearm to the hand.
The boundaries of Guyon canal are:
- Roof: palmar carpal ligament, palmaris brevis and hypothenar connective tissue.
- Floor: transverse carpal ligament, pisohamete ligament, pismetacarpal ligament, flexor digitorum profundus tendons and opponens digiti minimi.
- Medial wall: pisiform, abductor digiti minimi and flexor carpi ulnaris tendon.
- Lateral wall: hook of hamete, transverse carpal ligament and the flexor tendons.
Injury to the distal ulnar nerve can be due to compression, trauma, inflammation or vascular insufficiency.
- Ganglion cysts, they’re one of the most common causes of Guyon canal syndrome
- Anatomical anomalies, can be hypertrophic muscle of normal anatomy or unusual location
- Ulnar artery thrombosis or aneurysm (e.g., Hypothenar Hammer Syndrome)
- Fractures or dislocations (e.g., The hook of hamate Fracture/Displacement)
- Repetitive trauma (e.g., repetitive trauma to the hypothenar by the handlebar in cyclists)
- Carpel tunnel syndrome, it can lead to anatomical changes in the ulnar tunnel leading to functional impairments
As the ulnar nerve passes through Guyon’s canal it splits into deep motor branch and superficial sensory branch.
Guyon’s canal is divided into 3 zones, compression on the ulnar nerve at each zone results in specific symptoms.
Zone 1 compression refers to compression at the proximal end of Guyon’s canal, proximal to the bifurcation of the ulnar nerve into sensory and motor branches.
Compression at zone 1 leads to mixed sensory and motor symptoms resulting in sensory dificits over the hypthenar, little finger and the medial half of the ring finger and motor weakness of all ulnar innervated intrinsic muscles.
Zone 2 compression refers to compression only at the deep motor branch of the nerve, distal to the bifurcation.
Only motor symptoms would develop resulting in motor weakness in the hand muscles innervated by the ulnar nerve.
Compression at zone 2 may occur at pisohamete hiatus after the nerve to abductor digit minimi takeoff, which would result in weakness in the intrinsic muscles of the hand with possible sparing of the hypothenar muscles.
Zone 3 compression refers to compression at the superficial sensory branch, it manifests as sensory deficits on the palmer side of the ring finger and the palmer-medial side of the ring finger without hypthenar and interosseous weakness.
History And Physical Examination
Guyon’s canal syndrome is diagnosed clinically.
There may be history of repetitive trauma or stress to the hypothenar area of the hand. Long distance cyclists can acquire Guyon’s canal syndrome as a result of the handle bar pressure on the wrist.
The symptoms can be purely motor or purely sensory or both according to the site of compression.
The first step in physical examination is observation of the hand for clawing, atrophy of the hypothenar or interossei, inability to cross fingers or any masses over the wrist.
Tenderness over the hook of hamete can indicate fracture.
Tinel’s sign involves tapping over the location of suspected nerve compression would reproduce symptoms. Froment's sign is observed, when the patient is asked to hold a piece of paper between his thumb and fingers as the examiner tries to pulls it, weakness in adductor polices muscle (supplied by the ulnar nerve) would result in compensatory movement of thumb flexion instead of thumb adduction. The little finger is placed in an over-abducted position at rest, know as Wartenber's sign.
Classical radiographs including posteroanterior and lateral views.
Computed tomography scan (CT) is useful in cases of suspected hook of hamate fracture.
MRI and ultrasound are useful in the diagnosis.
Nerve conduction studies are useful in confirming the diagnosis and localizing neuropathies.
Management of Guyon canal syndrome is similar to that of carpel tunnel syndrome, it includes conservative management or surgical decompression.
Conservative treatment is recommended for mild and moderate symptoms with duration of less than 3 months. Surgical treatment is recommended for moderate to very severe symptoms with duration of at least 2 months.
Physical Therapy Management
Ulnar nerve glide exercise based on the Butler concept for the ulnar nerve is as follows: Wrist extension, forearm pronation elbow flexion, glenohumeral lateral rotation, glenohumeral depression, shoulder abduction.
The patient is instructed to avoid activities that cause repetitive stress at Guyon’s canal such as weight bearing or cycling or modification of the bicycle handlebars. Also, to avoid static postures or repetitive movements that places mechanical overload such as prolonged wrist extension.
The patient is instructed to wear resting hand splint to place the wrist in neutral position. The splint should be worn for 1-12 weeks during nighttime and at daytime during aggravating activities.
This management is from the European handguide study treatment guidlines. 
The aim of the surgery is to decrease the pressure on the ulnar canal in Guyon's canal by removing the roof of the Guyon canal or removing the structures compressing the nerve.
During the early post-operative period (up to 10-15 days after surgery), the patient is advised to elevate his hand, provide appropriate rest of the hand, do gradual hand and wrist movements without resistance as tolerated and to avoid applying heavy loads on the hand or doing forceful activities.
The post-surgical instructions include scar care, edema control, hand and wrist mobilization and ergonomics advice to avoid putting mechanical load on the nerve.
Splinting after surgery is not routinely indicated, it is indicated only for patients with severe pain after surgery and patients who are likely to put mechanical load on the canal.
Post-surgical exercises is indicated for patients with reduced hand mobility in a case of hand edema or the patient fearing using the hand, to promote nerve glide and to strengthen the muscles of the hand.
Brachial plexus abnormalities
Cervical disc disease
Traumatic peripheral nerve lesions
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