The median nerve runs the length of the arm, responsible for motor and sensory functions in the forearm and hand. Compression occurs when surrounding structures exert pressure, disrupting the nerve’s ability to transmit signals effectively. This condition, often referred to as an entrapment neuropathy, is a common source of chronic pain, numbness, and functional impairment in the upper extremity. Understanding the causes of median nerve compression is the first step toward finding relief from these symptoms.
Anatomy and Function of the Median Nerve
The median nerve originates high in the armpit from the brachial plexus, a network of nerves stemming from the lower neck and upper chest area. It descends through the arm before entering the forearm, where it supplies many of the muscles responsible for flexing the wrist and fingers.
The nerve provides both motor and sensory innervation to the hand. Its motor function controls most forearm flexors and the thenar muscles at the base of the thumb, which are responsible for thumb opposition and fine grasping.
The sensory component allows for feeling over the palm side of the thumb, index finger, middle finger, and the thumb-side half of the ring finger. When compressed, a person may experience difficulty with movement and altered sensation. The palmar cutaneous branch, which supplies sensation to the central palm, is often spared in carpal tunnel syndrome because it typically splits off higher and does not pass through the wrist.
Primary Sites and Causes of Nerve Entrapment
Compression of the median nerve can occur at several specific anatomical pinch points along its course. The most frequent location for entrapment is at the wrist, resulting in Carpal Tunnel Syndrome (CTS). The carpal tunnel is a narrow passageway formed by the wrist bones and the transverse carpal ligament.
Carpal Tunnel Syndrome (CTS)
The median nerve passes through this space along with nine flexor tendons. Swelling or thickening of these tendons or surrounding tissues increases pressure on the nerve. Causes of increased pressure include repetitive wrist movements, fluid retention (due to pregnancy or systemic conditions like diabetes and rheumatoid arthritis), and trauma such as a wrist fracture. High pressure impedes the nerve’s blood supply, leading to dysfunction.
Proximal Compression Sites
Proximal to the wrist, the nerve can be compressed in the forearm, a condition sometimes termed pronator syndrome. This often happens as the nerve passes between the two heads of the pronator teres muscle. Repetitive or forceful pronation movements can cause the muscle to tighten around the nerve.
Less common sites near the elbow include the ligament of Struthers and the lacertus fibrosus (bicipital aponeurosis). These proximal compressions are often related to anatomical variations or muscle hypertrophy.
Clinical Manifestations of Nerve Compression
Sensory disturbances are often the earliest and most recognizable signs of median nerve compression. Patients frequently report paresthesia, such as tingling or “pins and needles,” or numbness in the thumb, index, middle, and half of the ring finger.
These sensations commonly worsen at night, often waking the patient, or after sustained activities like driving or holding a phone. Pain can be localized to the hand and wrist but may also radiate upward into the forearm and sometimes the shoulder.
Motor symptoms develop as compression progresses, including weakness and clumsiness in the hand. This weakness makes tasks requiring fine motor control, such as buttoning a shirt or grasping small objects, difficult. In advanced, chronic cases, the thenar muscles at the base of the thumb may visibly waste away, indicating severe nerve damage.
Management and Relief Strategies
Initial treatment focuses on conservative, non-surgical approaches aimed at reducing pressure and inflammation.
- Wrist splints are a common first-line strategy, often worn at night to keep the wrist in a neutral position and minimize nerve pressure.
- Activity modification involves limiting repetitive movements or postures that exacerbate symptoms.
- Non-steroidal anti-inflammatory drugs (NSAIDs) may be used to manage pain and reduce inflammation.
- Corticosteroid injections directly into the compression area, such as the carpal tunnel, can provide temporary relief by reducing swelling.
- Physical therapy incorporates nerve gliding exercises to help the median nerve move more freely.
If symptoms persist, worsen, or if muscle wasting occurs despite conservative management, surgical intervention may be necessary. The most common procedure is carpal tunnel release surgery, which involves cutting the transverse carpal ligament to enlarge the tunnel and relieve pressure. This surgery is a reliable and definitive treatment option for cases that fail to respond to non-surgical methods.