Median Nerve Lesions: Causes, Symptoms, and Treatment

• These notes cover median nerve lesions, including their pathophysiology, etiology, symptoms, and treatment, as well as specific conditions such as Pronator Teres Syndrome and Carpal Tunnel Syndrome.

Median Nerve Lesions:

• The median nerve originates from the medial (C8, T1) and lateral (C5, C6, C7) cords of the brachial plexus (C5-C8 & T1).
• It travels down the medial side of the humerus from the axilla to the cubital fossa.
• The median nerve passes between the heads of the pronator teres, going distally deep in the forearm and becoming superficial at the wrist via the carpal tunnel, ending at digits 1-3.
• It innervates anterior forearm muscles like pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus.
• The median nerve provides sensory innervation to the skin over the thenar eminence/palm in line with digits 1-3, and the palmar surface/fingertips of digits 1-3 and the lateral half of 4.
• Injuries can include neuropraxia, axonotmesis, and neurotmesis.
• Damage can occur due to brachial plexus injuries, fractures/dislocations of the elbow, wrist, or carpal bones, compression from pronator teres or carpal tunnel, or trauma.
• Median nerve injuries have a higher risk of causalgia due to the autonomic fibers it contains.
• A complete median nerve lesion can cause muscle flaccidity in the forearm & hand, loss of thumb opposition, and inability to flex the 2nd and 3rd fingers.
• This can result in an "ape hand" appearance at rest and an "oath hand"/pope's blessing when attempting to make a fist.
• Autonomic dysfunction may lead to vasomotor & trophic changes such as edema, nail ridges, and thin glossy skin.

Pronator Teres Syndrome:

• It can occur as a neuropraxia or axonotmesis.
• Injury around the elbow can cause atrophy of forearm flexors & pronators, resulting in weakness in wrist flexion, abduction, and pronation.
• Compression can occur as the median nerve passes through the two heads of the pronator teres and also with Struther's Ligament.
• Symptoms include an achy, tired, heavy feeling in the forearm, numbness in the thumb & index finger, weakness/wasting in thenar muscles, and pain in the forearm with elbow movement.
• There are no nocturnal symptoms.
• Etiology involves repetitive movements of forearm/elbow or throwing sports.
• DDx includes C6 nerve root, CFT injury, carpal tunnel syndrome, or TrP's
• This requires alleviation of compression through attachment release of pronator teres, nerve glides, skin roll, solid forearm massage, forearm strengthening & stretching, and contrast hydrotherapy.

Carpal Tunnel Syndrome:

• It's a neuropraxia condition where the carpal tunnel is formed by the carpal bones on the bottom and the flexor retinaculum (transverse carpal ligament) on top.
• Ten structures pass through the carpal tunnel: the median nerve, 4 tendons each of flexor digitorum superficialis and profundus, and the flexor pollicis longus tendon.
• Compression reasons include decreased space in the tunnel (lesion, edema) or increased contents (inflammation, tendonitis).
• Symptoms include numbness/tingling in median nerve distribution, nocturnal discomfort due to venous stasis or compression, pain with wrist movement, potential forearm pain, and swelling.
• May additionally find hypertonicity of forearm flexors, adhesions around the flexor retinaculum, atrophy of thenar/index muscles, & clumsiness.
• If the compression is in the carpal tunnel, normal sensation may be found over the thenar area due to the palmar cutaneous nerve branching before the carpal tunnel.
• Etiology includes systemic conditions that increase fluid retention (diabetes, pregnancy, hypothyroidism), wrist fracture causing bony callus, ganglia, cysts, lunate dislocation, or arthritis.
• Common amongst meat packers, chefs, grocery clerks, assembly line workers, construction workers, massage therapists, chiropractors, and computer workers.

Assessments:

• Upper Limb Tension Tests (ULTT) can determine if shoulder/arm pain is due to nerve root or peripheral nerve pathology, performed with patient supine near the edge of the table.
• ULTT 1 tests the median nerve with the head neutral, humerus abducted to 110 degrees, extended 10 degrees, externally rotated 60 degrees, and with wrist & fingers extended.
• ULTT 2 tests the median, musculocutaneous, & axillary nerves with the head neutral, shoulder girdle depressed, humerus abducted to 10 degrees, wrist & fingers extended, and forearm supinated & elbow extended.
• The Pronator Teres Syndrome Test involves resisting active pronation or stretching the muscle.
• Phalen's Test involves placing the backs of hands together in wrist flexion for 1 minute.
• The Reverse Phalen's Test involves placing the palms of hands together & strongly presses together for 1 minute.

Treatment Goals:

• Treatment aims to decrease edema with support, cool compresses, axillary pump, and light effleurage.
• Other goals are to reduce compression on the nerve by releasing fascial restrictions, muscle stripping to decrease hypertonicity, release TrP's, & mobilize flexor retinaculum.
• Homecare includes ADL changes around wrist postures, ergonomics, stretches, strengthening exercises, hydrotherapy, and nerve glides.