Pathophysiology

Aetiology
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)
NB: the presence of non-occupational risk factors does not eliminate the possible role of occupational factors in the development of CTS. Indeed, patients with systemic illnesses may be more susceptible to the adverse effects of occupational exposures.

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.

 

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