GUYON CANAL SYNDROME
Carpal tunnel syndrome is not the only compressive neuropathy that can occur at the wrist. The flexor retinaculum forms the roof of the carpal tunnel and extends between the triquetral and the scaphoid. An extension of the retinaculum passes from the superficial and radial aspect of the triquetral to the flexor retinaculum and between the triquetral this fibrous extension and the flexor retinaculum itself a further fibro-osseous tunnel is formed which transmits the ulnar nerve and artery. This tunnel is referred to Guyon’s canal. Guyon’s canal syndrome refers to compression of the ulnar nerve within this fibro-osseous structure.

IMAGING
A ganglion cyst or synovial cyst arising from the adjacent pisiform triquetral joint is the commonest cause but neural-compression can also occur as a consequence of aneurysms of the ulnar artery or other soft tissue masses. Anomalous enlargement of the flexor digitorum brevis muscle has been described as a potential cause of ulnar nerve compression. Anomalous muscle enlargement is common however the prevalence of associated ulnar nerve compression secondary to it has not been fully evaluated
Look carefully at the PTJ for effusion or ganglion
Other causes include ulnar artery aneurysm
Accessory muscle are common and may be overstated as causes of this syndrome

Beyond Guyon's canal, the ulnar nerve divides into two branches, the superficial and deep .
The deep branch runs adjacent to the hook of the hamate and may be compressed against it.
The nerve may be found the to a ligament the runs between the pisiform and hamate.

RADIAL NERVE COMPRESSION / WARTENBERGS SYNDROME
Radial nerve injury as it traverses from the anterior to posterior compartment
Usually due to direct compression
Sometime called the ‘Third Crossover’ syndrome
Nerve affected as it passes from the flexor to the extensor compartment
The radial nerve is superficial in location and prone to direct injury