Carpal Tunnel Syndrome

Suneet Sood

Carpal tunnel syndrome is a set of symptoms and signs that develop when the median nerve is compressed in the carpal tunnel. Ashworth, 2013


The proximal carpal bones in the wrist include, from the radial side to the ulnar, scaphoid, the lunate, the truquetrum, and the pisiform. The distal ones, again from radial to ulnar, are the the trapezoid, the trapezium, the capitate and the hamate. In the dorsoventral plane, these bones form a shallow curve that is convex dorsally, and concave ventrally. Anteriorly, the flexor retinaculum (also called the “transverse carpal ligament”) [Moore and Dalley, 2006] stretches tightly across this curve, from the scaphoid and trapezoid to the pisiform and hamate bones. The space between the flexor retinaculum ventrally and the carpal bones dorsally is the carpal tunnel. The tunnel contains the flexor muscles of the hand (flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, flexor carpi ulnaris), and the median nerve. (Except for the flexor carpi ulnaris, the other structures are within a common synovial sheath.) The median nerve is the most sensitive structure here, and may become compressed when the carpal tunnel narrows. [Moore et al, 2010]


The median nerve supplies two and a half thenar muscles, as well as the first and second lumbricals. Its sensory innervation includes the entire palmar surface, the sides of the first three digits, three and a half digits on the radial side of the hand. Interestingly, the median nerve has a branch, the palmar cutaneous branch, that supplies the central palm. This branch does not pass through the carpal tunnel, and is spared in compressions of the tunnel. The median nerve also carries autonomic fibers to the hand, therefore autonomic symptoms may sometimes occur as well. [Moore et al, 2010]

Pathology [Ashworth, 2013]

The following are the risk factors for a carpal tunnel syndrome: [Ashworth, 2013]

  • Increasing age (typically >45 years)
  • Female sex (3-10 times more common in women than in men)
  • Increased body mass index (BMI)
  • Square-shaped wrist
  • Short stature
  • Dominant hand
  • Race (white)
  • Family history
  • Some medical conditions, including diabetes, hypothyroidism, hereditary neuropathies, recent menopause, dialysis, acromegaly, amyloidosis
  • Some professions and activities that are associated with prolonged forces acting at the wrist, or exposure to vibration/ cold
      Diseases that may cause a carpal tunnel syndrome include the following:

[Ashworth, 2013]

  • Wrist fracture (Colles)
  • Flexion/extension injury of the wrist
  • Lesions in the carpal tunnel: tenosynovitis, rheumatoid and othery types of arthritis at the wrist, ganglions, edema, or other lesions that may occupy space

Evaluating a patient with a suspected carpal tunnel syndrome


Symptoms may be sensory, motor, or autonomic. The commonest sensations are numbness and tingling, especially in the radial three and a half digits of the hand. Patients may say that their hands fall asleep. Pain may occur, and may radiate distally or even proximally. Motor symptoms include weakness: patients typically complain that things slip from their fingers. Autonomic symptoms include a sensitivity to cold, and, rarely, decreased sweating in the hand.

Examination [Bickley and Szilagyi, 2007; Ashworth, 2013]


  • Wasting of the “LOAF” muscles: Lumbricals (1st and 2nd), Opponens pollicis, Abductor pollicis brevis, and Flexor pollicis brevis
  • Square wrist sign: ratio of wrist thickness to width is greater than 0.7 (sensitivity, specificity about 70%)


  • Testing for altered sensation, two-point discrimination in the first three digits and the radial side of the 4th digit of the hand
  • Testing for weakness of the LOAF muscles
  • Palpation of the tissues directly over the median nerve at the wrist, for mechanical restriction (sensitivity over 90%, specificity over 75%)
  • Thumb abduction test for the carpal tunnel syndrome
  • Tinel’s sign in the carpal tunnel syndrome (low sensitivity and specificity)
  • Phalen’s test (specificity over 80%, low sensitivity)
  • Carpal tunnel compression test (sensitivity and specificity about 90%)

Investigations [Ashworth, 2013]

  • Consider tests to rule out medical disorders (e.g. diabetes, hypothyroidism), electrophysiological tests for nerve conduction and electromyography, as well as MRI studies of the wrist
  • Ashworth, NL. Carpal Tunnel Syndrome. Emedicine,, accessed 4 May 2014
  • Bickley LS, Szilagyi PG. Bates’ Guide to Physical Examination and History Taking, 9th edition, Lippincott Williams and Wilkins, Philadelphia, 2007, p555-556
  • Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 6th edition, Lippincott Williams and Wilkins, Philadelphia, 2010, p790-1
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