Dr. Ebraheim’s educational animated video describes the compression of the ulnar nerve in the Guyon's canal.

The ulnar nerve rises from the medial cord of the brachial plexus. After the ulnar nerve passes through the arm, it runs from the medial epicondyle to the pisiform bone in the wrist in a direct trajectory. Two carpal bones are important in relation to the ulnar nerve in the wrist:
1Pisiform
2Hamate
Both the ulnar nerve and artery enter the Guyon’s canal. The Guyon’s canal is approximately 4 cm long. The ulnar nerve enters the wrist medial to the ulnar artery. The Guyon’s canal has one proximal entrance and 2 distal exits: one superficial, one deep. The Guyon’s canal contains the ulnar nerve with its superficial sensory and deep motor branches.
Ulnar nerve compression neuropathy can occur in the Guyon’s canal.

Zones of Guyon’s canal compression
•Zone I:
Location: proximal bifurcation of the nerve
Symptoms: mixed motor and sensory
Common causes: ganglia and hook of hamate fractures.
•Zone II:
Location: deep motor branch
Symptoms: motor only.
Common causes: ganglia and hook of hamate fractures.
•Zone III:
Location: superficial sensory branch
Symptoms: sensory only
Common causes: ulnar artery thrombosis or aneurysm.
The deep branch of the ulnar nerve innervated all of the interosseous muscles and the 3rd and 4th lumbricals . it also innervates the hypothenar muscles, the adductor pollicis muscles, and the deep head of the flexor pollicis brevis muscle. The superficial branch of the ulnar nerve is mainly sensory. It gives supply to the digitial nerves if the 4th and 5th fingers and a motor branch to the palmaris brevis muscle.
Presentation/symptoms
•Based on the location of compression in the Guyon canal, the affected area of the nerve may be purely motor, purely sensory or a mixture or motor and sensory.
•Pain and paresthesia in the ulnar 11/2 digits
•Clawing of the 4th and 5th fingers
•Loss of the intrinsic (it normally flexes the MCP and extends the IP joints)
•In low ulnar nerve injury, the flexor digitorum profundus is working, flexing the 4th and 5th fingers and casuing the clawing.
•Ulnar nerve palsy resulting in paralysis of the intrinsic muscles, test the first dorsal interosseous muscle and check for atrophy.
•Weak pinch: 70% of pinch is lost due to loss of adductor muscles.
•Froment;s test is positive: when pinching a piece of paper between the thumb and index, the thumb IP joint will flex if the adductor pollicis muscle is weak due to ulnar nerve palsy.
•Weak grasp due to intrinsic weakness
•Wartenberg’s sign: abduction of 5th finger due to ulnar nerve palsy.
•Allen’s test: should be done to check for ulnar artery thrombosis.
•Carpal tunnel view xrays and CT scans are useful to evaluate hook of hamate fractures and nonunions.
•Ultrasound is useful to check vascular status and diagnose ulnar artery thrombosis.
•EMG and nerve studies are helpful.
Differential diagnosishigh or low ulnar nerve injury
•In low ulnar nerve injury or compression, the flexor digitorum profundus muscle is working, flexing the 4th and 5th fingers and causing clawing.
•High ulnar nerve palsy
Less clawing of the hand
Sensory deficit to the dorsum of the hand
In cubital tunnel syndrome you can also find:
Tinel’s sign at the elbow
Positive elbow flexion test.
The dorsal cutaneous branch arises before the Guyon’s canal. If you have high ulnar nerve palsy, there will be sensory deficit on the dorsum of the hand.
Treatment
•Nonoperative: activity modification, NSAIDS, splinting.
•Surgery: release of the carpal tunnel: in patients diagnosed with both carpal tunnel and ulnar tunnel, the Guyon’s canal is adequately decompressed by the release of the carpal tunnel. Local decompression especially if nonoperative treatment fails. Decompression of the ulnar nerve by addressing the cause. The success of surgery depends on finding a cause.

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Background music provided as a free download from YouTube Audio Library.
Song Title: Every Step