Carpal tunnel syndrome

 

Now that you’ve done that, try this:

Carpal tunnel contents:

• Flexor digitorum superficialis (4 tendons)
• Flexor digitorum profundus (4 tendons)
• Flexor pollicis longus (1 tendon)
• Median nerve
• Should be noted that the transverse carpal ligament, forming the volar (anterior) border of the carpal tunnel, is also known as the flexor retinaculum.

Median nerve course:

• Prior to entering the carpal tunnel:
  • Median nerve gives off the anterior interosseous branch and palmar cutaneous branch.
    • Anterior interosseous branch supplies flexor digitorum profundus and flexor pollicis longus.
    • Palmar cutaneous branch supplies the skin of the lateral palm.
• After coursing through the carpal tunnel:
  • Median nerve gives off the recurrent branch and palmar digital branch.
    • Recurrent branch of median nerve supplies opponens pollicis, abductor pollicis brevis, and superficial part of flexor pollicis brevis.
    • Palmar digital branch supplies the lateral two lumbricals. It also supplies sensation to the lateral palm and fingertips.

Carpal tunnel syndrome key symptoms:

• Paresthesias and/or numbness of the first 3.5 fingers and lateral palm.

• USMLE will often give forearm discomfort or numbness as well in carpal tunnel syndrome. Student says “wtf?” But this is common in exam questions.
• Weakness of the lateral hand, followed by atrophy of the thenar eminence, may be seen in untreated cases.
• The thenar eminence consists of:
  • Opponens pollicis
  • Abductor pollicis brevis
  • Flexor pollicis brevis
  • Note that it’s not an accident that these muscles are innervated by the recurrent branch of the median nerve and are also the ones affected in severe and/or ongoing carpal tunnel syndrome.

Who gets it:

1. Stereotypical vignette is that of an office worker who uses the computer all day.
2. USMLE also likes bilateral carpal tunnel syndrome in jackhammer operators (i.e., high force, vibrating tools).
3. Normal in pregnancy due to edema.
4. Hypothyroidism (edema + glycosaminoglycan deposition)
5. Acromegaly (enlargement of tendons).

Diagnosis:

• USMLE wants “electrophysiological testing” as the answer. This encompasses “electromyography and nerve conduction studies” (also an answer on NBME forms).
• Maneuvers such as Phalen test, Tinel sign, and carpal compression test are not sufficient for diagnosis.
• Phalen test → numbness elicited in the median nerve distribution within 60 seconds of maximal wrist flexion.

• Tinel sign → tapping of the flexor retinaculum elicits paresthesias in the median nerve distribution.

• Carpal compression test (Durkan test) → applying firm pressure over the proximal lateral palm for 30 seconds elicits paresthesias.

Treatment:

• “Wrist splint” is the answer on the USMLE.
• NSAIDs are not proven to be effective Tx.
• If wrist splints have been tried to no avail, USMLE wants “triamcinolone injection into the carpal tunnel” as the next answer. Triamcinolone is a steroid.
• Surgical answers such as endoscopic or open nerve decompression are always wrong on the USMLE.
• The “million dollar lawsuit” occurs when the median nerve is inadvertently transected during surgery, resulting in loss of function of the thumb.

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