GUYON’S CANAL SYNDROME

Definition:
Guyon’s canal syndrome, also known as Ulnar Tunnel Syndrome, is a relatively rare condition. It is caused by compression of the of the ulnar nerve at the level of Guyon’s canal and results in neurological (motor and/or sensory) symptoms in the 4^th/5^th digits and ulnar side of the palm (depending on the level of compression).¹ It typically presents in cyclists due to prolonged compression of the ulnar nerve against the handlebars and has been colloquially known as “handlebar palsy”.² Although anatomical variations are well documented, the accepted anatomical boundaries of Guyon’s canal include:^1, 3, 4

• Floor: transverse carpal ligament, pisohamate ligament, pisometacarpal ligament, flexor digitorum profundus tendon, opponens digiti minimi tendon
• Roof: palmar carpal ligament, palmaris brevis tendon, hypothenar connective tissue
• Medial wall: Pisiform, abductor digiti minimi and the tendon of the flexor carpi ulnaris
• Lateral wall: Hook of the hamate, transverse carpal ligament, flexor tendons

Figure 1 – Volar Wrist – Anatomy of floor and roof of Guyon Canal.
Floor is formed by the flexor retinaculum extending transversely across carpal bones, and roof is formed by the pisohamate ligament (ligament attaching pisiform to hook of hamate).

CA – Capitate, Ha – Hamate, Hk – Hook of hamate, Lu – Lunate, Sc – Scaphoid, Td – Trapezoid, Tm – Trapezium

Figure 2 – Route of Ulnar Nerve through Guyon canal

CA – Capitate, Ha – Hamate, Hk – Hook of hamate, Lu – Lunate, Ra – Radius, Sc – Scaphoid, Td – Trapezoid, Tm – Trapezium, Ul – Ulna
There are three major types of Guyon Canal Syndrome described:¹Type 1: compression of the complete trunk or both branches of the ulnar n in the proximal portion of the canal. Results in sensory & motor defecits Type 2 (most prevalent): Isolated compression of the deep terminal motor branch ulnar n. Superficial branch is unaffected. Results in isolated motor weakness. Type 3 (least common): Isolated compression of the superficial branch of the ulnar n. Results in isolated sensory symptoms.
Mechanism of Injury: Prolonged compression of the ulnar nerve in Guyon’s canal.¹ It typically presents in cyclists secondary to pressure applied against the handlebars and has been colloquially known as “handlebar palsy”. This injury can also be develop by repetitive compressive trauma in karate and in baseball, particularly in catchers. ⁵
Differential Diagnosis TFCC tear, Hamate contusion, ECU tenosynovitis/tendinosis, Pisiform fracture/contusion, Systemic etiologies of peripheral neuropathies (DM, vit B12 def, folate def, etc), elbow ulnar neuropathy
Exam: Inspection: May observe wasting of hypothenar muscles. Neurological exam: Sensory deficit on the volar 5^th and ulnar side of 4^th digit. Motor weakness in ulnar nerve distribution (all intrinsic hand muscles). Special tests: Tinnel’s of the ulnar nerve may be positive. Investigations: NCS and EMG can confirm diagnosis and characterize degree of injury.
Management: ¹ Avoid aggravating activities that compress the canal. Padding to build up around canal as opposed to over it will help relieve pressure. For cyclists a change in hand position may also improve symptoms and there are also gloves with built in padding to help relieve pressure over the canal. Neutral wrist splint with fingers free for 1-12 weeks (at least worn at night) Surgical decompression if nonsurgical management as failed.

References:

1. Hoogvliet P, Coert JH, Friden J, Huisstede BM, European Hg. How to treat Guyon’s canal syndrome? Results from the European HANDGUIDE study: a multidisciplinary treatment guideline. British Journal of Sports Medicine 2013;47:1063-70.
2. Capitani D, Beer S. Handlebar palsy–a compression syndrome of the deep terminal (motor) branch of the ulnar nerve in biking. Journal of Neurology 2002;249:1441-5.
3. Pierre-Jerome C, Moncayo V, Terk MR. The Guyon’s canal in perspective: 3-T MRI assessment of the normal anatomy, the anatomical variations and the Guyon’s canal syndrome. Surgical and Radiologic Anatomy 2011;33:897-903.
4. Bozkurt MC, Tagil SM, Ozcakar L, Ersoy M, Tekdemir I. Anatomical variations as potential risk factors for ulnar tunnel syndrome: a cadaveric study. Clinical Anatomy 2005;18:274-80.

Dr. David Lawrence  (June 30, 2014, PR   ND)