The carpal tunnel is a crucial anatomical structure located in the wrist region. It serves as a passageway for important structures, including the long flexor tendons and the median nerve. This WordPress post delves into the details of the carpal tunnel, its components, anatomical borders of the flexor retinaculum, and clinical considerations.

Anatomy of the Carpal Tunnel

The carpal tunnel is formed by the concave anterior surface of the carpal bones and is closed off by a band of connective tissue called the flexor retinaculum. Within this tunnel, several structures are tightly packed together, including the long flexor tendons of the fingers, their synovial sheaths, and the median nerve. The flexor retinaculum acts as a protective band, holding these structures in place and preventing excessive movement.

Components of the Carpal Tunnel

1. Flexor Retinaculum: This thickened band of deep fascia stretches across the front of the wrist and converts the concave anterior surface of the hand into the carpal tunnel. It is attached medially to the pisiform bone and the hook of the hamate, and laterally to the tubercle of the scaphoid and the trapezium bones. The attachment points of the flexor retinaculum serve as the anatomical borders.
2. Long Flexor Tendons: The tendons of the flexor digitorum superficialis and flexor digitorum profundus muscles pass through the carpal tunnel. The four tendons of the flexor digitorum superficialis muscle are arranged in anterior and posterior rows, while the tendons of the flexor digitorum profundus muscle lie behind them. All eight tendons invaginate a common synovial sheath known as the ulnar bursa.
3. Median Nerve: The median nerve runs alongside the flexor tendons within the carpal tunnel. It passes between the flexor digitorum superficialis and flexor carpi radialis muscles. Any compression or reduction in the size of the carpal tunnel can result in the median nerve becoming compressed, leading to a condition known as carpal tunnel syndrome.

Anatomical Borders of the Flexor Retinaculum

The flexor retinaculum, a key component of the carpal tunnel, has specific anatomical borders that contribute to its structure and function. These borders define the lateral and medial limits of the retinaculum. Here are the anatomical borders of the flexor retinaculum:

• Lateral Border: The lateral border of the flexor retinaculum is formed by the tubercle of the scaphoid bone and the crest of the trapezium bone. These bony prominences provide attachment points for the retinaculum and help to maintain the integrity of the carpal tunnel laterally.
• Medial Border: The medial border of the flexor retinaculum is defined by the pisiform bone and the hook of the hamate bone. These structures serve as attachment points for the retinaculum and contribute to the stability and structure of the carpal tunnel medially.

Understanding the anatomical borders of the flexor retinaculum provides insights into the spatial relationships within the carpal tunnel. These borders play a crucial role in maintaining the proper alignment and functioning of the structures passing through the tunnel.

Carpal Tunnel Syndrome: Clinical Considerations

Carpal tunnel syndrome is a common condition characterized by compression of the median nerve within the carpal tunnel. It typically presents with symptoms such as burning pain, tingling sensation (“pins and needles”), weakness in the lateral three and a half fingers, and a loss of muscle bulk in the thenar region. The compression of the median nerve can result from various causes, including thickening of the synovial sheaths surrounding the flexor tendons or arthritic changes in the carpal bones.

Tinel’s Sign: Tinel’s sign is a diagnostic manoeuvre used to identify nerve irritation or injury. Specifically, in the context of carpal tunnel syndrome, Tinel’s sign is performed by gently tapping or percussing over the course of the median nerve at the wrist. If the nerve is compressed or injured, the patient may experience a tingling or “pins and needles” sensation radiating along the path of the nerve. This tingling sensation indicates nerve hypersensitivity or irritation and is considered a positive Tinel’s sign. The test helps to localize the site of median nerve compression or injury within the carpal tunnel.

Phalen’s Sign: Phalen’s sign is another clinical test used to assess median nerve compression in the carpal tunnel. The test is performed by having the patient flex both wrists at 90 degrees while keeping the elbows on a table or surface for about 60 seconds. In a positive Phalen’s sign, the patient may experience pain, numbness, or tingling in at least one finger innervated by the median nerve. The test evaluates the vulnerability of the median nerve to compression when the wrist is flexed, as this position can further reduce the space within the carpal tunnel and exacerbate symptoms.

Clinical presentation and diagnosis of carpal tunnel syndrome involve a thorough assessment of symptoms, physical examination, and sometimes additional tests such as nerve conduction studies. Initially, conservative measures are employed to reduce inflammation and alleviate symptoms. These measures may include lifestyle modifications, wrist splinting, and medication.

In cases where conservative measures fail to provide relief, surgical decompression of the flexor retinaculum may be necessary. This procedure, known as carpal tunnel release, aims to alleviate pressure on the median nerve by creating a longitudinal incision through the flexor retinaculum, thereby expanding the carpal tunnel.

Understanding the anatomy and clinical implications of the carpal tunnel is crucial for healthcare professionals involved in the diagnosis, treatment, and management of carpal tunnel syndrome. By considering the anatomical borders, structures within the tunnel, and the underlying pathology, healthcare providers can deliver appropriate care tailored to each patient’s needs.