Carpal tunnel syndrome (CTS) has long been one of the most common work-related disorder as well as the most prevalent peripheral neuropathy. The syndrome is characterized by the weakness in the thumb, index and middle finger, numbness, tingling and even paralysis due to muscle atrophy. These symptoms result from the compression of the median nerve. There are many causes traditionally associated with the disorder including trauma, overuse and systemic conditions. While a great deal of information is known on the disorder, and in the recent years many steps have been taken and have been sucessful at reducing the disorder, the prevalence and cost to society is still very high. By re-examining the data using an evolutionary perspective to understand why the carpal tunnel is susceptable to the disorder compared to other species and what are current human patterns that increase an individual’s chance of developing CTS, the causes of the disorder can be better understood and more prevenative actions can be taken.
The wrist is made up of eight carpal bones which articulate proximally with the radius and ulna of the forearm and distally with the metacapals of the hand. The carpal bones are aligned in two rows. The proximal row containing the scaphoid, lunate, triquetral and pisiform and the distal row which consists of the trapezium, trapezoid, capitate and hamate. The ventral side of the carpal bones creates a concave cavity. This cavity is known as the carpal tunnel. The tunnel is formed by the the transverse carpal ligament (TCL) which stretch across the top of the carpal bones (Fig.1.) .
The TCL is a thick inflexible connective tissue that attaches medially to the pisiform and the hook of the hamate and attaches laterally to the tubercle of the scaphoid and the trapezial ridge . The tunnel contains the median nerve and nine flexor tendons. The nine tendons connect each of the fingers and the thumb to the muscles of the forearm to allow flexing of the fingers as well as clenching of the fist . The flexor digitorum superficialis and the flexor digitorum profundus are each surrounded by a single synovial sheath, which connect to each of the four fingers in the hand. The ninth tendon is the flexor pollicis longus. This tendon is also surrounded by a synovial sheath and leads into the thumb. The median nerve runs superficial to the tendons2.
The path of median varies by individual, however the median nerve will often branch into radial and ulnar components once it enters the carpal tunnel. The radial component supplies motor branches to the abductor pollicis brevis, the opponens pollicis and the superficial head of the flexor pollicis brevis (together these muscles make up the thenar eminence) and sensory branch or ulnar component leads to the palmar surface of thumb and the first and second fingers. Damage to the radial component of the median nerve can lead...