Introduction

Ulnar Tunnel Syndrome, also known as Guyon Canal Syndrome, is a neuropathic condition resulting from the compression of the ulnar nerve at the wrist as it passes through Guyon's canal. This condition leads to sensory and motor deficits in the hand, affecting daily activities and overall quality of life. The following review is based on the detailed study by Brandon E. Earp et al., titled "Ulnar nerve entrapment at the wrist," published in the Journal of the American Academy of Orthopaedic Surgeons.

Anatomy and Pathology of the Ulnar Tunnel

Zone 1: Proximal Canal

Anatomy: Zone 1 includes the section of the ulnar nerve before it bifurcates into its sensory and motor branches. The ulnar nerve enters Guyon’s canal at its proximal end along with the ulnar artery. The boundaries of the canal in this zone are formed by the pisiform bone medially, the hook of the hamate laterally, the transverse carpal ligament dorsally, and the volar carpal ligament ventrally. This region is critical because it encompasses the main trunk of the ulnar nerve before it divides, making it susceptible to compressive forces from various sources.

Pathology: Compression in Zone 1 can be caused by several factors, including:

• Ganglia: These are cystic swellings that can press on the nerve.
• Lipomas: Benign fatty tumors that can cause compression.
• Fibrous Bands: These can form due to repetitive stress or congenital anomalies.
• Fractures of the Hook of the Hamate: Traumatic injuries can lead to bony prominences that compress the nerve.

These pathological entities can exert pressure on the nerve trunk, leading to both sensory and motor deficits since the entire nerve is involved before it bifurcates into its respective branches.

Zone 2: Distal Motor Branch

Anatomy: Zone 2 encompasses the deep motor branch of the ulnar nerve. This branch innervates several intrinsic muscles of the hand, including:

• Hypothenar Muscles: Responsible for movements of the little finger.
• Interossei Muscles: Important for finger abduction and adduction.
• Adductor Pollicis: Essential for thumb adduction.
• Third and Fourth Lumbricals: These muscles assist in finger flexion at the metacarpophalangeal joints.

The deep motor branch travels beneath the fibrous arch of the hypothenar muscles after diverging from the main ulnar nerve trunk.

Pathology: Compression in Zone 2 often results from:

• Repetitive Trauma: Activities that involve extensive use of the hand can lead to hypertrophy and compression.
• Ganglia Arising from the Triquetrohamate Joint: These cysts can impinge on the motor branch.
• Hypertrophic or Anomalous Muscles: Overdeveloped muscles can compress the nerve, especially in individuals with repetitive strain from occupational or recreational activities.

Because this zone involves the deep motor branch, compression here primarily affects motor functions without sensory involvement, leading to weakness in the intrinsic muscles of the hand.

Zone 3: Superficial Sensory Branch

Anatomy: Zone 3 involves the superficial sensory branch of the ulnar nerve, which provides sensory innervation to the palmar aspect of the little finger and the ulnar half of the ring finger. This branch diverges from the ulnar nerve trunk within Guyon’s canal and travels superficially.

Pathology: Common causes of compression in Zone 3 include:

• Ulnar Artery Thrombosis: Blood clots in the ulnar artery can compress the nearby nerve.
• Aberrant Musculature: Abnormal muscle structures can encroach on the sensory branch.
• Soft Tissue Masses: Lipomas, ganglia, or other benign growths can compress the nerve.

Compression in this zone typically leads to isolated sensory deficits without affecting motor functions, causing numbness and tingling in the ulnar distribution of the hand.

Symptoms

Patients with ulnar tunnel syndrome can present with a variety of symptoms depending on the specific zone of compression:

• Numbness and Tingling: Sensory disturbances in the hypothenar eminence, little finger, and ulnar half of the ring finger.
• Pain: Discomfort or aching in the wrist and hand.
• Weakness: Difficulty with fine motor tasks, such as gripping objects or typing, due to weakness in the intrinsic hand muscles.
• Muscle Atrophy: In severe or chronic cases, wasting of the hypothenar muscles and other ulnar-innervated intrinsic muscles.

Diagnosis

History and Physical Examination:

A thorough history and physical examination are critical in diagnosing ulnar tunnel syndrome. Key elements include:

1. Detailed Patient History:

   • Onset, duration, and severity of symptoms.
   • Occupational and recreational activities that might contribute to repetitive wrist stress.
   • Any history of trauma to the wrist or hand.
   • Previous medical conditions, such as diabetes or arthritis, that might predispose to neuropathy.

2. Physical Examination:

• Motor Examination:
  • Grip and Pinch Strength: Assess the strength of grip and pinch, comparing with the unaffected hand.
  • Froment’s Sign: Weakness in the adductor pollicis muscle indicated by thumb flexion when pinching paper.
  • Wartenberg’s Sign: Inability to adduct the little finger due to interosseous muscle weakness.
  • Intrinsics Testing: Weakness in the hypothenar muscles, interossei, and adductor pollicis muscles.
• Sensory Examination:
  • Two-Point Discrimination: Testing the ability to distinguish two points on the skin, which helps localize sensory deficits.
  • Light Touch and Monofilament Testing: Assessing the sensation in the ulnar nerve distribution.
  • Tinel’s Sign: Tapping over Guyon's canal to elicit tingling in the ulnar nerve distribution.
• Vascular Examination:
• Pulse Assessment: Checking for ulnar artery pulse while palpating for any thrill or pulsatile mass.
• Allen Test: Assessing the patency of the arterial arch system in the hand to rule out ulnar artery thrombosis.
• Doppler Examination or Arteriography: May be necessary for further evaluation of vascular involvement.

Imaging and Electrodiagnostic Studies:

1. X-rays: Useful for identifying bony abnormalities such as fractures of the hook of the hamate.
2. Ultrasound: Can visualize soft-tissue masses and assess for dynamic changes with wrist movement.
3. MRI: Provides detailed images of the nerve, surrounding soft tissues, and any pathological changes within the canal.
4. Nerve Conduction Studies (NCS): Measure the speed and amplitude of electrical signals along the ulnar nerve to identify areas of slowed conduction.
5. Electromyography (EMG): Evaluates the electrical activity of muscles innervated by the ulnar nerve to detect denervation or reinnervation changes.

Management

Non-Surgical Treatments

1. Activity Modification: Avoiding activities that exacerbate symptoms, such as repetitive wrist flexion and prolonged pressure on the ulnar side of the hand.
2. Splinting: Using a wrist splint to immobilize the wrist and reduce pressure on the ulnar nerve.
3. Medications: Nonsteroidal anti-inflammatory drugs (NSAIDs) to reduce pain and inflammation.
4. Physical Therapy: Exercises to improve nerve gliding and strengthen the muscles around the wrist.
5. Injections: Corticosteroid injections for short-term relief.

Surgical Treatments

Surgery is considered for patients who do not respond to conservative treatment or present with significant motor weakness and atrophy.

1. Decompression Surgery:
   • An incision is made over the Guyon canal to release the structures compressing the ulnar nerve.
   • Postoperative care includes immobilization followed by rehabilitation to restore strength and function.
2. Ulnar Nerve Transposition:
• The ulnar nerve is relocated from its position within the canal to reduce compression.
• This procedure is considered if there is recurrent compression.

Conclusion

Ulnar Tunnel Syndrome, or Guyon Canal Syndrome, is a complex condition that requires a thorough understanding of the anatomical zones and their associated pathologies. Proper diagnosis and treatment are crucial to preventing permanent nerve damage and restoring hand function. By recognizing the specific symptoms and applying appropriate diagnostic tools, healthcare providers can tailor their treatment strategies to achieve optimal outcomes for patients suffering from this condition.

References

1. Earp, Brandon E., et al. "Ulnar nerve entrapment at the wrist." JAAOS-Journal of the American Academy of Orthopaedic Surgeons 22.11 (2014): 699-706.