Ulnar Nerve Entrapment

Left ulnar nerve

My patient who is a Team Singapore cyclist came in with a case of ulnar nerve entrapment on Friday. Ulnar nerve entrapment* is the second most common nerve condition happening in the upper limb after carpal tunnel syndrome.

The ulnar nerve arises from the brachial plexus at C8-T1 and travels down the inner part of the upper arm through the arcade of struthers (pictured below).

At the elbow, the ulnar nerve travels just behind the bony part on the inner part of the elbow. This is also know as the "funny bone" when you can get sensations of pins and needles after bumping the area. 

Picture by Conor Jones

As the ulnar nerve crosses the elbow, it passes through a bony tunnel and up to 2 other potential points for blockage making it vulnerable to pressure or stretching. Prolonged periods of sleeping with the elbow bent can also cause over stretching of the nerve. My patient hurt her ulnar nerve after riding for a few hours in a new position after changing her handlebars. Riding for a few hours on bumpy roads did not help. She had also fractured both her clavicles (R followed by L in the last few months). This is also known as the cubital tunnel syndrome.

The ulnar nerve supplies the sensation and muscles to the 5th and half the ring finger. Symptoms are related to degree of irritation of the nerve. They start off intermittent in nature and may only come on at night after the nerve has been stretched for a longer time. 

Pins and needles, aching or tingling in the little and/ or ring finger will be the common symptoms. This is what my patient felt. If the irritation persists, the symptoms may become constant and progress to numbness in the 5th and/ or ring finger and ultimately weakness in the hand.

As the ulnar nerve exits the bony tunnel, it goes into the flexor carpi ulnaris muscle. Follwing that at the wrist, it travels superficially to the flexor retinaculum and passes into Guyon's canal.  

R wrist

Guyon's canal is formed by 4 borders (pictured above). The roof is the palmar carpal ligament, the floor being the transverse carpal ligament, the ulnar (inner) border is the pisiform and the radial (outer) border is hook of hamate.  If the nerve is irritated at the wrist it is known as Guyon's canal syndrome.

Picture from Medical Art Library

The flexor carpi ulnaris and inner half of flexor digitorum profundus muscles are innervated by the ulnar nerve and the hypothenar muscles (pictured above).

Knowing the exact site of nerve irritation during an accurate clinical examination will help decide what needs to be done for treatment. Some doctors send their patients to do a nerve conduction test, but I personally find that an upper limb tension test (with radial nerve bias) done correctly does a much better job. Others may do ultrasound imaging to help diagnosis. Do not confuse it with thoracic outlet syndrome.

Just remember not to have a steroid/ cortisone injection.

*Ulnar nerve entrapments are commonly seen in cyclists, golfers, weightlifters and construction workers.

References

Kong G, Brutus JP, Vo TT et al (2023). The Prevalence Of Double- And Multiple Crush Syndromes In Patients Surgically Treated For Peripheral Nerve Compression In The Upper Limb. Hand Surg Rehabil. 42(6): 475-481. DOI: 10.1016/j.hansur.2023.09.002

Raut P, Jones N, Raad M et al (2022). Common Peripheral Nerve Entrapments In The Upper Limb. Br J Hosp Med. 83(10): 1-11. DOI: 10.12968/hmed.2022.011

Have a look at this ulnar nerve video.