A 28-year-old dentist consults her physician, complaining that she feels tingling and slight pain in her right hand. The symptoms are localized to her thumb, index, middle and lateral side of her ring finger. The sensations are more intense at night or if she overworks. Recently, she has experienced some weakness in her grasp and finds it more difficult to hold her instruments. Also, movements of her right thumb are not as strong as before.
On examination, there is loss of power on certain movements of the thumb. She has impaired appreciation of light touch and pin pricks to the thumb, index, middle and lateral side of her ring finger, but sensation to her palm is not affected. Pressure and tapping over the flexor retinaculum causes tingling. After a complete examination, the patient is diagnosed with carpal tunnel syndrome.
Questions to consider:
- What is the carpal tunnel? What is contained in it?
The carpal tunnel is a canal at the wrist made up of the carpal bones and flexor retinaculum. The tunnel houses the tendon of the flexor pollicis longus in its synovial sheath, the tendons of the flexor digitorum superficialis and profundus in their common synovial sheath and the median nerve.
- Two muscles that are affected by carpal tunnel syndrome are the abductor pollicis brevis and the opponens pollicis. How would you test their function?
The abductor pollicis brevis pulls the thumb away from the palm at a right angle. One way to test this is to lie the forearm on a table, palm up and ask the patient to point their thumb towards the ceiling. At the same time, you can push down on the thumb to give some resistance.
The opponens pollicis pulls the thumb across the palm towards the base of the little finger. Ask the patient to do this against resistance.
- Physicians used to think this kind of pain was caused by a deficiency in the brachial plexus. If this was the case, what roots or trunks would have to be involved and why is this unlikely to be the cause of the problem? (Consider both sensory and motor deficiencies that this patient has.)
If this patient's symptoms were caused by a deficiency in the brachial plexus, practically all roots from C6 to T1 would have to be involved. The sensory dermatome of that region comes from the ventral rami of C6 and C7, which compose part of the upper and all of the middle trunk of the brachial plexus. The motor supply to the muscles involved come from segments of C8 and T1. Such a widespread lesion, however, would be unlikely to have such limited symptoms.
- What causes the symptoms of carpal tunnel syndrome?
Carpal tunnel syndrome is caused by a compression of the median nerve. This can be due to the inflammation of the common flexor tendon sheath after strain and overexertion. Fluid retention, as seen in pregnancy and hormonal imbalances, can also cause compression of the nerve. Patients often feel an increase in symptoms at night due to venous stasis. Venous stasis contributes to the compression of the nerve.
- Although this patient recovered with rest and physical therapy, some patients do not improve with conservative treatment and opt for surgery. What structures might be endangered by surgery and need to be avoided?
Surgery can decompress the median nerve. Structures superficial to the flexor retinaculum, however, can be endangered. This includes the superficial palmar vascular arch formed by the superficial branch of the ulnar artery and superficial branch of the radial artery, the palmar cutaneous branches of the median and ulnar nerves and the recurrent motor branch of the median nerve.