Carpal tunnel syndrome (CTS) is a prevalent condition that affects millions of people worldwide, causing pain, numbness, and tingling in the hand and fingers. This condition arises from pressure on the median nerve as it travels through the carpal tunnel in the wrist. But what exactly happens inside the wrist, and why does it lead to nerve dysfunction? Let’s explore the science behind carpal tunnel syndrome.

Understanding the Carpal Tunnel The carpal tunnel is a narrow passage in the wrist formed by bones and ligaments, through which the median nerve and tendons pass. This nerve controls sensation and movement in the thumb and first three fingers. Under normal conditions, these structures glide smoothly within the tunnel, allowing for seamless hand function.

What Happens in Carpal Tunnel Syndrome? In CTS, swelling or inflammation within the carpal tunnel compresses the median nerve, disrupting its ability to send signals to the hand. This leads to symptoms such as pain, tingling, weakness, and numbness, particularly in the thumb, index, and middle fingers. Over time, untreated CTS can result in muscle atrophy and permanent nerve damage.

• Mechanical Compression: The median nerve is compressed within the carpal tunnel, often due to fibrosis of the subsynovial connective tissue (SSCT). This fibrosis restricts the normal gliding of the nerve and tendons, increasing pressure within the tunnel and leading to nerve compression. This mechanical compression can cause structural changes in the nerve fibers, including elongated nodes, which are indicative of adaptive responses to chronic compression [Festen-Schrier & Amadio, 2018; Schmid et al, 2014].
• Ischemic Injury: Increased pressure within the carpal tunnel can obstruct venous return, leading to intrafunicular anoxia and subsequent intrafunicular edema. This edema increases intrafunicular pressure, impairing blood supply and ultimately destroying nerve fibers through ischemic injury. The ischemic environment can also lead to oxidative stress and cellular injury, further exacerbating nerve damage [Sunderland, 1976; Sud & Freeland, 2005].[3-4]
• Neuroplastic Changes: Central neuroplastic changes are also implicated in CTS. Patients with CTS exhibit maladaptive cortical neuroplasticity, including delayed somatosensory cortical responses and altered beta oscillations. These changes are associated with the severity of peripheral nerve dysfunction and contribute to the sensory symptoms experienced by patients. Functional deficits in CTS reflect reorganization of the primary somatosensory cortex, which correlates with symptom severity and sensory discrimination accuracy [Fernández-de-Las-Peñas et al, 2020; Maeda et al, 2014].

What are the Causes and Risk Factors for Carpal Tunnel Syndrome? Several factors contribute to the development of CTS, including:

• Repetitive Hand Movements: Frequent use of the hands, especially in activities like typing, knitting, or using vibrating tools, increases the risk.
• Medical Conditions: Diabetes, rheumatoid arthritis, thyroid disorders, and pregnancy can increase fluid retention, leading to nerve compression.
• Genetics: A naturally smaller carpal tunnel can predispose some individuals to CTS.
• Injury or Trauma: Fractures or sprains affecting the wrist can alter tunnel space and lead to nerve compression.

What are the Symptoms of Carpal Tunnel Syndrome? The hallmark symptoms of CTS include:

• Numbness or tingling in the thumb, index, and middle fingers
• Weak grip strength and difficulty holding objects
• Hand pain that worsens at night
• A sensation of swelling in the fingers, even when no visible swelling is present

Conclusion Carpal tunnel syndrome is a progressive condition that can significantly impact hand function and quality of life. Understanding its causes and early symptoms can lead to timely intervention, preventing long-term nerve damage. If you experience persistent hand pain or numbness, seeking medical advice is crucial for effective treatment and recovery.

References

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2. Festen-Schrier VJMM, Amadio PC. The biomechanics of subsynovial connective tissue in health and its role in carpal tunnel syndrome. J Electromyogr Kinesiol. 2018 Feb;38:232-239.
   
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