Carpal Tunnel Syndrome

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Introduction

  • Carpal Tunnel Syndrome occurs when median nerve gets squished in the wrist causing pain, numbness, tingling and in more severe cases, weakness and clumsiness of the hands
  • Most common compressive neuropathy in the upper extremity

Anatomy

  • The median nerve arises from the C6,C7,C8 and T1 segments of the spinal cord
  • Roots  from C6 and C7 provide sensory fibers which transmit sensation from the radial 3.5 fingers  (i.e. thumb to medial ½ ring finger)
  • Roots from C8 and T1 provide motor fibers which supply muscles in the
    • Forearm
      • Pronator teres
      • Flexor carpi radialis
      • Palmaris longus
      • Flexor digitorum superficialis
      • Pronator quadrates
    • Hand
      • Abductor pollicis brevis
      • Flexor pollicis brevis
      • Opponens pollicis
      • 1st and 2nd lumbricals
  • As it enters the wrist, the median nerve passes through the carpal tunnel a space enclosed by the transverse carpal ligament on the palmar side and carpal bones on the other 3 sides
  • Median nerve shares this tunnel with 9 flexor tendons
  • The carpal tunnel is smaller in diameter compared to males

Pathogenesis

  • Inflammation or thickening of flexor tendons can result in increased pressure in the carpal tunnel
  • Studies investigating the compression of human nerves show
    • Swelling and thickening of vessel walls in the endoneurium and perineurium
    • Vascular proliferation
    • Thinning of the myelin
    • Nerve fiber degeneration and regeneration
  • Damage to the myelin or vessels supplying the nerve cause
    • Decreased conduction velocity
    • Possibly, axonal loss
  • As a result, signals transmitted by the median nerve would be slowed or eventually
  • Sensory fibers seem to be more sensitive to compression than motor fibers perhaps explaining why sensory findings often precede motor findings in CTS
  • Early in the disease
    • There is no structural changes in the nerve
    • Neurologic symptoms are
      • Reversible
      • Intermittent
  • Prolonged episodes of increased pressure in the carpal tunnel can lead to
    • Segmental demyelination of the nerve
    • Increased frequency
    • Increased severity of symptoms
  • Prolonged ischemia can result in axonal injury and potentially irreversible nerve dysfunction
  • Macroscopically, surgical reports describe an "hourglass" shaped deformity of the median nerve in the carpal tunnel which may reflect thinning of the nerve under the transverse carpal ligament and/or swelling of the nerve distal or proximal to transverse carpal ligament

Risk factors

  • Associated with
    • Aromatase inhibitor use
    • Obesity
    • Pregnancy; due to fluid accumulation
    • Diabetes
    • Rheumatoid arthritis
    • Hypothyroidism
    • Amyloidosis
    • Connective tissue disease
    • Median mononeuropathy
    • Acromegaly; due to tendon sheath enlargement
    • Trauma to wrist
  • It is not caused by work, any more than running after the bus causes heart disease
  • Occupation may precipitate symptoms in patients with underlying disease
    • Prolonged use of hand-held vibratory tools
    • Repetitious flexion and extension of the wrist with forceful gripping
    • There is little/no evidence to support a relationship with keyboarding

Prevention

  • Studies suggest splinting may alter the underlying course of CTS

Nutritional factors

  • AAOS gudelines state that there is insufficient evidence to recommend for or against nutritional supplements or specific supplementation with vitamin B6 as treatment for carpal tunnel syndrome

Natural History

  • Incidence : 1-3 cases per 1000 people per year
  • Prevalence : 50 cases per 1000 people in the general population
  • Male : Female 1:8
    • Bilateral involvement is common in females
    • More common in menopausal women
  • Usually 40 - 50 years old
  • Younger patients usually have associated factors

Clinical Presentation

  • Symptoms usually include burning, numbness or tingling on the palmar side of the thumb, index finger, middle finger and radial half of ring finger sparing the little finger
  • Symptoms amy relieve by hanging the arm at the side of the bed or walking around
  • Pain may radiate up the arm
  • "Classic symptoms" in sensory distribution of the median nerve have
    • 61% sensitivity
    • 71% specificity
  • Patients often report worsening of symptoms at night. Nocturnal symptoms have
    • 51-77% sensitivity
    • 27-68% specificity
  • Loss of two point discrimination in fingers supplied by the median nerve occurs in later stages of disease and has low sensitivity and high specificity
  • Provacative tests
    • Tinel's sign: elicit by taping just proximal to the site of impingement
    • Phalen's test: hands flexed at wrist (consider negative if no symptoms after one minute)
    • Modified Phalen's test: hold pressure over carpal tunnel while flexing the wrists (consider negative if no symptoms after one minute)
    • Reverse Phalen's test: Extending wrists in a prayer-like position (consider negative if no symptoms after one minute)
    • Durkan's test: Hold pressure over carpal tunnel
      • Consider negative if no symptoms after one minute
      • Low sensitivity and specificity (36% and 57%, respectively)

Diagnositc criteria

  • Numbness and tingling in the median nerve distribution
  • Nocturnal numbness
  • Weakness and/or atrophy of the thenar muscles
  • Tinel sign
  • Phalen's test
  • Loss of 2-point discrimination

Late presentation

Denervation of the muscles of the hand supplied by the median nerve causes

  • Decreased grip strength
  • Decreased strength in opposition of the thumb resulting from

Differential Diagnosis

  • More Proximal Lesion of Median Nerve
    • Can be caused by dislocation of ulna
    • Findings in hand would be similar
    • Distinctive features : weakness of muscles of the forearm supplied by median nerve
  • Radiculopathy
    • C6 or C7 radiculopathy could look similar with similar findings in the hand
    • Distinctive features
      • Neck pain
      • Muscle weakness and sensory findings proximal to the carpal tunnel
  • Ulnar neuropathy
    • Has similar description of numbness and tingling in the fingers
    • Distinctive features : patients would describe funny feelings in the little finger and ulnar side of the ring finger
  • Pronator teres syndrome
  • Hereditary neuropathy
  • AIN syndrome

Psychosocial impact of disease

  • The psychosocial impact of the disease depends on the
    • Patient's occupation
    • Lifestyle
    • Disease severity
  • Decreased grip strength and increased clumsiness and frequency of dropped objects can be a significant source of impairment for people accustomed to working with their hands

Imaging and Diagnostic Studies

Carpal tunnel syndrome is a clinical diagnosis

X-Ray

  • Can be used to rule out possible causes of increased pressure within the carpal tunnel such as fracture to the carpal bones or distal radius
  • Imaging studies are not routinely used to evaluate CTS

Ultrasound

  • Ultrasound has shown that patients with CTS have increased cross sectional area of the median nerve compared to controls
  • However, there is no cut off point for diagnosis of CTS

MRI

  • MRI can be used postoperatively to evaluate the quality of the release

Electrodiagnostic studies

  • Nerve conduction studies measure conduction velocity of the median nerve in the carpal tunnel
  • The role of electrodiagnostic testing is uncertain
  • Electrodiagnostic testing is useful to
    • Confirm the diagnosis preoperatively, as a baseline for monitoring unexpected outcomes
    • Rule out other conditions such as radiculopathy, and for Workers Compensation cases
    • If repeat testing is necessary for a patient, be sure to send them to the same lab
  • Mild CTS may not show any alterations in conduction
  • Demyelination can occur with increased compression, resulting in conduction block or slowed conduction across the wrist
  • EMG's may not normalize post op but they will improve
  • In a 2002 systematic review of prospective studies
    • The sensitivity of nerve conduction studies for CTS ranged from 56 - 85%
    • The specificity ranged from 94 – 99%

Treatment

Non-operative

  • Vitamin B6 does not significantly improve overall symptoms compared with placebo
  • Wrist splint : Immobilise the wrist to avoid positions which increase carpal tunnel pressure
  • NSAIDs
    • Relieve pain
    • Decrease inflammation
  • Oral steroids
  • Steroid injection
    • Injection of corticosteroids into the carpal tunnel to decrease inflammation
    • Have been shown to be better than placebo injections
    • A good response to an injection is prognositic of a better response to surgery compared to those who do not respond to the injection
    • May be used for therapeutic and prognostic reasons
    • Surgical decompression is recommended when injection no longer provides relief

Surgery

  • Cut fascial covering of carpal tunnel to decrease pressure
  • Options
    • Open carpal tunnel release (OTCR)
    • Endoscopic carpal tunnel release (ETCR)
      • No difference in outcomes at 1 year post op
      • Less postoperative pain
      • Shorter return to functional activities
      • The most significant, proven advantage of ECTR is faster mean return to work (18 days for ECTR vs. 38 days for OCTR)

Opponensplasty

  • Patients with severe weakness and atrophy of the thenar muscles have a low likelihood of regaining their strength
  • In these cases an opponensplasty may be indicated. Options include:
    • Camitz Procedure : transfer of palmaris longus tendon to the abductor pollicis brevis insertion site
    • Royle-Thompson Procedure
      • Transfer of ring FDS to thumb
      • Tendon is routed around ulnar border of the palmar fascia to act as a pulley
      • A slip of the superficialis is attached to the neck of the first metacarpal
      • Another slip is drawn over the MP joint and sutured into the hood mechanism of the proximal phalanx

Re-operation

  • Reoperation for persistent CTS occurs in less than 5% of cases
  • The most common reason for revision is technical error during primary release
    • Incomplete release of flexor retinaculum in 55%
    • Nerve adhesion in scar tissue in 32%
    • Nerve laceration in 6%
    • No known cause in 7%

Outcome

  • Wrist splints
    • 80% patients report that a wrist splint alleviates symptoms within days
    • May minimize symptom severity and functional deficits for up to 3 months
  • Oral steroids : May offer a benefit for up to 8 weeks
  • Steroid injection
    • Improves symptoms in 75% of patients
    • May provide benefit for 2 weeks to 6 months
    • Long-term benefits have not been shown
  • Surgery
    • Both OCTR and ECTR are safe and effective methods
    • Pain relief occurs within days
    • It takes several months for hand strength to return to preoperative levels
    • 70% of patients are either completely or partially satisfied with results
    • 79-90% patients report being free of nocturnal pain after surgery
    • 30% of patients over the age of 65 with chronic symptoms will not improve postoperatively

Complications

  • Untreated, the syndrome can progress to
    • Permanent sensory loss
    • Paralysis of the thenar muscles
  • Steroid injections
    • Infection
    • Rupture of tendons
    • Irritation of nerves
    • Possible systemic toxicity (hyperglycemia or hypertension)
  • Surgery
    • General
      • Infection
      • Bleeding
      • Ligation of the median nerve
    • OTCR
      • Scar tenderness
      • Higher risk of bowstringing of flexor tendons, particularly when associated with a flexor tendon repair
    • ETCR
      • Visualization is not as good as with the open technique
      • The risk of major nerve or vessel injuries is not increased
      • There is higher risk of
        • Incomplete release
        • Revision surgery
        • Transient neuropraxia of the digital nerves

References


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