CTS is frequently classified as a cumulative trauma disorder (CTD), or alternatively a repetitive strain injury (RSI), causing median nerve compression and trauma. It is characterized by pain, numbness, and paraesthesias in the cutaneous distribution of the median nerve with weakness and/or atrophy of the thenar muscles.
Risk Factors
CTS causation is likely multifactorial. Risk factors for CTS can be categorized into non-occupational and occupational risk factors.
Occupational risk factors
Occupational Risk Factor |
Job Title |
Job Duty |
Rapid work pace |
Grocery checker |
Scanning items |
Assembly line worker (Ex. automobile manufacturer) |
Handling objects on conveyor belts |
|
Repetitive motion |
Typist, clerical worker |
Keyboarding, mouse use |
Fish/fruit/vegetable canning worker |
Scaling fish, peeling fruits/vegetables |
|
Forceful exertions |
Construction trades worker |
Framing, demolition |
Industrial worker |
Heavy lifting, Ex. sheet metal |
|
Non-neutral body postures |
Dental hygienist |
Teeth cleaning |
Massage therapist |
Large muscle massage |
|
Hand-arm vibration |
Rock/quarry driller, miner |
Operation of crushers (platform, impact, roller, etc.) |
Cold temperatures |
Meat/poultry/food manufacturer |
Cutting, de-boning in temperature controlled rooms |
Hand intensive activities |
Aesthetician |
Small tool use |
Textile/garment worker |
Sewing details on jeans |
|
Combination of several risk factors |
Mechanic |
Air-powered tool use underneath a car on a lift |
The above risk factors can cause tendinosis, tendinitis, or tenosynovitis all of which have the potential to increase the pressure within the carpal tunnel. The structures within the carpal tunnel are vulnerable to elevated pressures because neither the carpal bones nor the flexor retinaculum are distensible.
Non-occupational risk factors
In addition to the above, other conditions that cause swelling of the wrist joint also have the potential to lead to median nerve compression and trauma. Including,
- Trauma or fracture of the carpals or distal radius/ulna
- Pregnancy (hormonal changes and water retention)
- Rheumatoid arthritis
- Osteoarthritis
- Collagen vascular diseases
- Renal failure
- Diabetes mellitus
- Thyroid disorders
- High BMI
- Female gender
- Sports (presumably the risk is mediated by the same factors as in WRCTS, particularly repetitive and forceful hand activities)
Ultimately all predisposing conditions and risk factors lead to a final common pathway where raised pressure within the carpal tunnel leads to raised pressure within the nerve itself. Intraneural vessels respond to this elevated intraneural pressure by becoming more permeable. Subsequently, edema forms within the nerve and the intraneural vessels are further compressed, causing ischemia. It is thought that in the short-term ischaemia is responsible for the intermittent tingling paraesthesias. In the long-term, continued deprivation results in nerve injury, demyelination and eventual axonal disruption, leading to numbness, anaesthesia, and/or hypalgesia.