PNS: Median Nerve

Median Nerve Anatomy and Objectives

• Focus is on treatment and management of Peripheral Nervous System disorders, specifically median nerve lesions.
• Learning objectives include discussing median nerve anatomy, common injuries, clinical presentation, assessment options, and treatment of carpal tunnel syndrome.

Median Nerve Pathway

• Starts at the medial (C8, T1) and lateral (C5,6,7) cords of the brachial plexus.
• Travels down the medial side of the humerus from the axilla to the cubital fossa.
• Passes between the heads of pronator teres, just distal to the elbow joint on the medial side.
• Travels distally deep in the forearm, becoming more superficial at the wrist as it passes through the carpal tunnel.
• Terminates at digits one to three.
• Anterior forearm muscles receive innervation from this nerve.

Etiology of Median Nerve Lesions

• Damage can occur due to brachial plexus injuries.
• Fractures of the elbow, wrist, or carpal bones can cause damage although humeral fractures rarely do.
• Dislocations of the elbow, wrist, or carpals, particularly lunate and scaphoid (FOOSH injuries), can result in median nerve lesions.
• Compression of the median nerve occurs from the pronator teres or carpal tunnel due to fibrosis, inflammation, or hypertonicity.
• Trauma, including traction, contusion, and laceration, can cause damage.

Symptoms of Median Nerve Lesions

• Presents as neuropraxia or axonotmesis, and muscle flaccidity in the forearm and hand with complete nerve lesions.
• Thumb opposition is lost and the second and third fingers cannot flex.
• "Ape Hand" is the resting appearance from loss of flexion in the second and third digits and inability to oppose the thumb.
• Attempting to make a fist will result in an "oath hand/Pope's blessing/hand of benediction" appearance.
• Autonomic function can be altered, resulting in vasomotor and trophic changes like edema, nail ridges, and thin, glossy skin.
• There is a risk of causalgia- persistent, severe burning pain.
• Atrophy of forearm flexors and pronators, wrist flexion weakness, abduction, and pronation may occur when damage is near the elbow.

Pronator Teres Syndrome

• On the medial side of the elbow, the nerve passes through the two heads of pronator teres, which can be a site of compression.
• A ligament (Struther's) runs from the medial epicondyle to the supracondylar ridge in 1-13% of individuals, potentially compressing the nerve.
• Repetitive movements of the forearm and elbow, using a screwdriver, racquet, baseball, and massage therapy may be causes.
• Symptoms onset gradually with an achy, tired feeling in the forearm numbness in the thumb and index finger
• Weakness/wasting can occur in thenar muscles, pain in the forearm is felt with elbow movement rather than wrist, and there are no nocturnal symptoms.

Carpal Tunnel Syndrome

• The carpal tunnel is formed by carpal bones at the bottom and the flexor retinaculum (transverse carpal ligament) at the top.
• The ligament is attached to the pisiform, hook of hamate, scaphoid tubercle, and trapezium.
• Structures passing through the carpal tunnel include: the median nerve, four tendons of FDS, four tendons of FDP, and the tendon of FPL.
• Numbness and/or tingling in the median nerve distribution are common symptoms.
• Nocturnal dysesthesia (discomfort) results from venous stasis or compression with wrist flexion.
• Additional symptoms: pain with wrist movement, limiting ROM-forearm pain, peripheral edema, hypertonicity of forearm flexors, flexor retinaculum adhesions (RSI), and thenar & index muscle atrophy.
• The median nerve branches off via the palmar cutaneous nerve before passing through the tunnel.
• Normal sensation will be present over the thenar area when the median nerve is compressed within the tunnel.
• Abnormal sensation over the median nerve distribution occurs when compressed proximal to the tunnel.
• Repetitive wrist flexion and extension, inflammation, edema, and fibrosis are etiologies.
• Increase in diabetes, pregnancy, and hypothyroidism are systematic conditions that increase fluid retention.
• Ganglia and cysts, lunate dislocations, RA, and wrist fracture that causes a bony callus are etiologies.
• Meat packers, chefs, grocery clerks, assembly line workers, construction workers, massage therapists, chiropractors, and computer workers are at risk.

Assessment - Upper Limb Tension Tests

• Used to determine if shoulder or arm pain is due to a nerve root or peripheral nerve pathology.
• These tests are useful when ROM is restricted.
• The patient being tested needs to be supine, near the edge of the table.
• Maintain the shoulder in depression while moving the arm and hand.

Upper Limb Tension Test #1 - Median Nerve

• The patient needs to be positioned with their head in neutral.
• Abduct the humerus to 110 degrees and extend by 10 degrees.
• The humerus should be rotated externally to 60 degrees.
• Tingling in 1, 2, 3 is normal when wrist and fingers are extended.
• Extend elbow with supination.
• Repeat the test with the head side bent away from the test side if no symptoms are recreated.

Upper Limb Tension Test #2 - Median, Musculocutaneous & Axillary Nerves

• The head is in neutral.
• The shoulder girdle needs to be depressed.
• Abduct the humerus to 10 degrees.
• Extend the wrist and fingers.
• Forearm should be supinated and the elbow extended.
• The test can be further sensitized by bending the head away from the side being tested.

Pronator Teres Syndrome Tests

• Active pronation should be resisted and then stretched.

Carpal Tunnel Syndrome Tests - Phalen's Test

• The patient is seated.
• Wrists should be flexed, and the elbows should be horizontal with the shoulders relaxed; the backs of the hands need to be placed and compressed together for 1 minute.
• This maneuver places maximum compression on structures in the tunnel.
• Positive test consists of tingling or pain in digits 1, 2, 3, and 1/2 of 4.

Carpal Tunnel Syndrome Tests – Reverse Phalen's Test

• This test is a variation of Phalen’s.
• The patient should place their hands with the palms together while strongly pressing for 1 minute.
• The test is positive if tingling and/or pain are reproduced in digits 1, 2, 3, and ½ of 4.

Treatment Goals for Carpal Tunnel Syndrome

• Support the arm with a pillow.
• Cool compress.
• Axillary pump.
• Light stroking of the skin, effleurage.
• Reduce the compression of the nerve (if possible) using fascia to target restrictions on the forearm to promote skin rolling and spreading.
• Muscle stripping should be used to reduce hypertonicity.
• Trigger points (TPs)s should be released.
• The flexor retinaculum should be mobilized.
• ROM & joint play needs to be assessed.