Median nerve injury

How does the median nerve run?

The median nerve is one of the main nerves of the upper limb. It is responsible for innervating most of the muscles of the forearm and some of the muscles of the hand. The median nerve is one of the branches of the brachial plexus, running along the arm in the medial part, first running at the brachial artery and then crossing it from the front in the lower part of the arm. It runs close to the skin and is relatively easy to access. At the level of the elbow, it passes between the two heads of the recurved obturator muscle, where it is protected by surrounding muscular and bony structures. It then runs in the front of the forearm, between the finger flexor muscles, innervating them. At the final stage, the median nerve passes through the carpal canal, innervating the glenoid muscles of the thumb and the glabellar muscles (the intrinsic muscles of the hand) in the hand. It is responsible for sensation in the skin of the thumb, index finger, middle finger and half of the ring finger (palmar part).

What functions does the median nerve perform?

The median nerve performs many important functions, both motor and sensory, in the upper limb. It is responsible for innervating the muscles and skin of the forearm and hand.

Motor functions:

• The obturator converse muscle: is responsible for converting the forearm (internal rotation).
• Radial wrist flexor muscle: enables flexion and extension of the wrist.
• Palmar longus muscle: helps to tighten the palmar cleft and flex the wrist.
• Finger superficial flexor muscle: enables flexion of the fingers at the proximal interphalangeal joints.
• Long thumb flexor muscle: flexes the thumb.
• Deep flexor muscle of the fingers: enables flexion of the fingers at the distal interphalangeal joints (lateral part, fingers II and III).
• Quadriceps recurvatore muscle: is responsible for the recurvatore of the forearm.
• Short thumb inversor muscle: is responsible for the inversion of the thumb.
• Thumb opposer muscle: enables the thumb to oppose the thumb.
• Short thumb flexor muscle: is responsible for flexing the thumb.
• Glabellar muscles (for fingers II and III): allow flexion of the fingers at the metacarpophalangeal joints and straightening at the interphalangeal joints.

Sensory functions:

• Responsible for sensation in the skin of the palmar part of the thumb, index finger, middle finger and half of the ring finger.
• The inside of the palm in this part is innervated by the cutaneous branches of the median nerve.
• It provides sensation on the palmar surfaces of fingers I-III and the lateral half of the ring finger.
• It is also responsible for sensation on the dorsal surfaces of these fingers, in the area from the fingertips to the distal interphalangeal joints.

How does damage to the median nerve occur?

• Mechanical injuries - Fractures of the bones of the arm, forearm or wrist can damage the median nerve. Particularly dangerous are fractures of the lower part of the humerus, which can directly compress or cut the nerve. Injuries resulting from cutting the skin and soft tissues, such as from accidents, can damage the median nerve. Similarly, dislocation of the elbow or wrist joint can also lead to nerve damage.
• Nerve compression (compression) - The most common cause of damage to the median nerve is carpal tunnel syndrome. The nerve is compressed in the carpal tunnel, leading to pain, numbness, tingling, weakness in the hand muscles and impaired sensation.
• Inflammatory conditions - inflammation of the synovial bursae in the wrist area, or inflammation of the tendon sheaths of the flexor muscles, can also lead to compression of the nerve.

Symptoms of damage to the median nerve

• Weakness or paralysis of the muscles of the forearm and hand innervated by the median nerve.
• Difficulty bending the wrist and fingers, especially the thumb.
• Problems with inverting and opposing the thumb.
• Pain, tingling, numbness in the area innervated by the median nerve (thumb, index finger, middle finger and half of the ring finger).
• Reduced sensation in these areas.
• Symptoms characteristic of carpal tunnel syndrome.

What is the treatment process for median nerve injury?

The treatment process for median nerve damage depends on the cause, the degree of damage and the patient's symptoms. Diagnosis is key, i.e. a detailed medical history of the symptoms, their severity, duration and possible injury, as well as a physical examination to assess muscle strength, range of motion and neurological tests (e.g. Phalen test, Tinel test). Imaging studies can be helpful in diagnosis: MRI, ultrasound, X-ray - they help assess the structure of the nerve and surrounding tissues, as well as EMG (electromyography) and ENG (nerve conduction study).

The mainstay is conservative treatment including: rest and restriction of movements that can aggravate symptoms. Splints or stabilizing bands can be used to relieve symptoms, especially at night (such as in carpal tunnel syndrome). The doctor may prescribe pharmacotherapy: anti-inflammatory drugs, painkillers, corticosteroids. Physiotherapy - strengthening and stretching exercises and massage - can have good results.

In more difficult cases, one moves on to surgical treatment involving nerve decompression (releasing the nerve from pressure points, such as decompression in the carpal tunnel in cases of carpal tunnel syndrome), suturing or reconstruction of the nerve (in cases of severe mechanical damage) or removal of obstructions (tumors, cysts or other structures compressing the nerve). The final step in the treatment of a median nerve injury is post-operative rehabilitation, which includes movement and strengthening exercises to restore full nerve and muscle function.

Prognosis

When treating a median nerve injury, the prognosis depends on the severity of the nerve damage and the speed of treatment. Minor damage has a better prognosis, while severe damage may require a longer recovery time and may not always lead to a full return of function. The process of treating a median nerve injury is usually a multi-step process and requires cooperation between the patient and the medical team - an orthopedist and a physiotherapist.

Related articles:

• Learn about other possible causes of wrist pain.
• Carpal tunnel syndrome.
• Carpal tunnel exercises.

Bibliography:

• National Library of Medicine - Median Nerve Injury - Alexander M. Dydyk; Guillermo Negrete; Gurpreet Sarwan; Marco Cascella. - 2023
• Ortho Bullets - Median nerve - Benjamin C. Taylor MD - 2016
• Uniwersytet Jagielloński Collegium Medicum - Elektrofizjologiczna ocena uszkodzenia nerwu pośrodkowego w zespole cieśni nadgarstka - Marta Banach - 2001