Carpal tunnel syndrome (CTS) is a medical condition in which a nerve is compressed as it travels through a tunnel in the wrist. This tunnel is called the Carpal Tunnel. As a result of the compression on the nerve, the affected individual may experience pain, numbness and tingling.
What is the Carpal Tunnel?
The carpal tunnel is a compartment located at the base of the palm. Through this tunnel pass nine tendons and the nerve (known as the median nerve). This nerve provides sensation to the thumb, index finger, long finger, and half of the ring finger. At the level of the wrist, the median nerve supplies the muscles at the base of the thumb that allow it to abduct, move away from the other four fingers, as well as move out of the plane of the palm.
How does the carpal tunnel compress the nerve?
The carpal tunnel is bordered on the anterior surface by the transverse carpal ligament, also known as the flexor retinaculum. The flexor retinaculum is a strong, fibrous band that attaches to the pisiform and the hamulus of the hamate.
What causes the symptoms?
The carpal tunnel is a distinct area. Therefore any compression to this may cause symptoms to t he area that the median nerve supplies. For example swelling may cause compression of the carpal tunnel. If there is ongoing swelling, then the nerve starts to “atrophy” (deteriorate). As a result the muscles that are affected by the median nerve may start to look wasted, and there may also be a loss of sensation in the affected areas.
The main symptom of CTS is intermittent numbness of the thumb, index, and middle (long) fingers and the radial (thumb) side of the ring finger. The numbness often occurs at night. Pain may extend up the arm, leading to discomfort extending to the shoulder and forearm. Long-standing CTS leads to permanent nerve damage, with constant numbness, atrophy of some of the muscles, which may result in clumsiness, or weakness of grip.
In addition to the history, there may be clinical signs, including reduced sensation, and weakness in the affected muscles and symptoms may be evoked with provocation tests. Nerve conduction studies may demonstrate the effect on the compressed nerve.
Atroshi JAMA, 1999 surveyed 3000 individuals in Sweden, with a response rate of 83%. 14.4% reported upper limb symptoms, 3.8% satisfied the clinical definition of CTS and 2.7% met the clinical and electrophysiological requirements for a diagnosis of CTS.
There are a variety of contributing factors.
Some of the individual predisposing factors include:
and a narrow-diameter carpal tunnel. Women suffer more from CTS than men with a ratio of 3:1 between the ages of 45–60 years. Only 10% of reported cases of CTS are younger than 30 years. Increasing age is a risk factor.
The relationship between work and CTS is controversial.
Occupational causes involve use of the hand and arm, such as:
· heavy manual work,
· work with vibrating tools,
· and highly repetitive tasks,
Even if they involve low force motions. Some speculate that the exposure can be cumulative. CTS may also result from an injury that causes internal scarring or mis-aligned wrist bones. A 2010 survey by NIOSH showed that 2/3 of the 5 million carpal tunnel cases in the US that year were related to work. Women have more work-related carpal tunnel syndrome than men.
Among current carpal tunnel syndrome cases attributed to specific jobs.
· 24% were attributed to jobs in the manufacturing industry,
· grocery store workers,
· frozen food factory workers (Hagberg, Scand J Work Environ Health 1992),
· meat and fish processing plants (Kim JY, Kim JI, Son JE, Yun SK. J Occup Health 2004)
· carpet layers (Kutluhan S: Int Arch Occup Environ Health 2001).
Conservative treatments include use of night splints and corticosteroid injection. The only scientifically established disease-modifying treatment is surgery to cut the transverse carpal ligament. This is known as “carpal tunnel release” surgery.
Early surgery with carpal tunnel release is indicated where there is:
· EMG evidence of median nerve denervation
· Static (constant, not just intermittent) numbness, muscle weakness, or atrophy,
· When night splinting or other conservative interventions no longer control intermittent symptoms.
In general, milder cases can be controlled for months to years, but severe cases are unrelenting symptomatically and are likely to result in surgical treatment.
Most people relieved of their carpal tunnel symptoms with conservative or surgical management experience minimal residual or “nerve damage”. Long-term chronic carpal tunnel syndrome can result in permanent “nerve damage”, i.e. irreversible numbness, muscle wasting, and weakness. While outcomes are generally good, certain factors can contribute to poorer results that have little to do with nerves, anatomy, or surgery type.
· One study showed that mental status parameters or alcohol use yields much poorer overall results of treatment.
· Workers with contested claims were less likely and slower to RTW & full duties than non-contested W/C cases. Return of grip strength slower and less complete. Olney Jr, Quezner DE Malowsky M Iowa Orthop J 1999.
Recurrence of carpal tunnel syndrome after successful surgery is rare.