The common flexor tendons can be affected by similar disease processes to tendons elsewhere including
tenosynovitis
tendinopathy and
tendon rupture
Carpal tunnel syndrome is a common disorder resulting in compression of the median nerve within the common flexor tunnel.
The tunnel contains the superficial and profundus tendons along with flexor pollicis longus.
The tendons are contained within a bony tunnel roofed by the flexor retinaculum.
Any cause which increases the volume of contents within the canal have the potential to compress the median nerve.
Tenosynovitis is a common cause however many patient's with carpal tunnel have no precipitating factor when the conditon is called idiopathic carpal tunnel syndrome.
The clinical diagnosis is relatively straightforward though in some patients with concurrent cervical spondyloarthritis, differentiating from neural compression in the cervical spine can cause problems.
In these instances the imaging findings can be helpful
Both MRI and ultrasound can be used to estimate the degree of median nerve compression.
A commonly is technique compares the circumference of the nerve cross-section of the nerve at the level of the pronator quadratus proximal to the carpal tunnel
with a cross-section of the nerve within the tunnel itself.
A difference of 12 mm2 is considered significant although it should be appreciated that there is overlap with the asymptomatic population.
Less common causes of carpal tunnel compression include masses including benign fatty tumors.
The occasionally the median nerve is bifid with the 2 portions of the nerve separated by a persistent median artery.
Seen in around 18% of normal population
Total cross sectionis larger than a normal nerve so associated with an increased incidence of CTS
Unilteral is more common than bilateral
The bifed nerve is most commonly assymmerical, with the two divisions differenr sizes
Once the diagnosis is made, the carpal tunnel can be injected with a mixture of corticosteroid and local anaesthetic.
A transverse approach under durect ultrasound guidance via an ulnar approach places the needle within the carpal tunnel
where it can be position both superficial and deep to circumferentially inject the nerve.
