It is 4 cm long, beginning proximally at the transverse carpal ligament and ending at the aponeurotic arch of the hypothenary muscles.
Guyon’s canal is a fibro-osseous tunnel that extends from the transverse carpal ligament in the proximal aspect of the pisiform to the origin of the hypothenary muscles in the hook of the hamate.
Guyon’s canal anatomy
- Roof: palmar ligament, palmaris brevis muscle, and hypothenar connective tissue.
- Floor: transverse carpal ligament, pisohamate ligament, pisometacarpal ligament, tendons of the deep flexor of the fingers and abductor muscle of the middle finger.
- Lateral wall: hamate hook, transverse carpal ligament and flexor tendons.
- Medial wall: pisiform bone, flexor carpi ulnaris tendon, adductor muscle of the little finger.
- Ulnar nerve: it bifurcates within the canal towards the deep (more radial) and superficial (more ulnar) branches.
- Ulnar artery and ulnar vein.
- Veins associated with the ulnar nerve.
At the level of the hamate hook, the canal forks into two canals: the first canal contains the superficial ulnar nerve and the ulnar artery, and the second canal contains the deep ulnar nerve.
These are separated by the fibrous arch of the flexor digiti minimi brevis, or the muscle itself attaches to the hook of the hamate.
The digiti minimi muscle may occasionally have an abnormal presence in Guyon’s canal. It was present in 25% of the population and can cause compression leading to Guyon’s canal syndrome.
It was described and named by Dr. Jean Casimir Felix Guyon, a French urologist in 1861.
Guyon’s canal syndrome
Guyon’s canal syndrome or ulnar nerve syndrome or manubrial palsy are the result of compression of the ulnar nerve as it passes through Guyon’s canal.
The epidemiology of Guyon’s canal syndrome is not well documented due to a paucity in the literature.
Some conditions that make patients more prone to developing Guyon’s canal syndrome are ganglion cysts, hamate fracture hook, and repetitive trauma (common in cyclists due to handlebar compression).
Guyon’s canal contains the deep branch of the ulnar nerve, which branches into a motor and a sensory branch. Symptoms depend on the involvement of the various branches of the ulnar nerve and include the following:
- Pain and impaired sensation in the ulnar middle of the sensory supply of the deep branch of the ulnar nerve.
- Weakness in flexion, abduction and opposition of the little finger (interaction of the hypothenary muscles).
- Weakness in digit adduction and abduction (interosseous innervation).
- Extension of the MCP and flexion of the PIP (innervation to the third and fourth lumbrical) resulting in the characteristic ulnar claw.
Radiography of the wrist may be helpful in identifying hamate hook fractures.
Ultrasound is helpful in identifying ulnar artery thrombosis, which can result in compression of the ulnar nerve. Ganglion cysts and soft tissue tumors such as lipomas that cause compression of the ulnar nerve can also be identified.
Abnormally thick ligaments, muscle variant, and nerve pathways can also be identified.
Magnetic Resonance (MRI)
Magnetic resonance imaging is only indicated in patients who have symptoms inconsistent with ultrasound findings, symptoms that persist after surgery, and a suspicion of massive injury.
T1-weighted MRI is the preferred method for identifying structures in Guyon’s canal.
MRI findings are similar to ultrasound, however, MRI is more sensitive and accurate. Additionally, the size and intensity of the ulnar nerve signal can be assessed on an MRI.
Treatment and prognosis
Treatment of Guyon’s canal syndrome is dictated by its etiology.
Conservative treatment includes physical therapy exercises, non-steroidal anti-inflammatory drugs (NSAIDs), and wrist bands.
Surgery may be indicated in some patients who have not responded to conservative treatment or if an acute cause such as ulnar artery thrombosis has been identified.