Wrist, Hand and Foot LO 4

4. Describe the carpal tunnel and explain the mechanism and consequences of carpal tunnel syndrome.

The carpal tunnel is formed at the wrist by carpal bones and connective tissue. The carpal bones form a concavity (C-shape with the opening on the ventral side) through which tendons from forearm muscles and the median nerve pass. The concavity is covered (and held in shape) by the transverse carpal ligament (sometimes referred to as flexor retinaculum).

The tendons are wrapped in synovial sheaths which act, like bursae, to reduce friction as the tendons pass through a tight compartment. In the image below, notice the tendon of the flexor pollicis longus adjacent to the median n. on one side and the tendons of the superficial digital flexors on the other side as they pass through the carpal tunnel.

In addition to the tendons of the extrinsic digital flexors passing through the carpal tunnel, the median n. does as well. Note that the ulnar n., and the radial and ulnar aa. and vv. do not pass through the tunnel. If the space of the carpal tunnel is reduced (potentially by inflammation of the synovial sheaths, thickening of the transverse carpal ligament, or other causes (flex and extend your wrist and think about which position creates more or less space)), the median nerve can be compressed. This compression can affect the “downstream” branches of the nerve – so, the cutaneous branches and/or the recurrent branch of the median n. Think about what symptoms one would have if any of these branches of the median nerve were compromised.