By Dr. Murray Heber, DC, BSc(Kin), CSCS, CCSS(C) resident
Head Chiropractor - Performance Enhancement Team - Bobsleigh Canada Skeleton

Cyclists palsy, or sometimes called Handlebar palsy is a relatively common condition in road cyclists and mountain bikers.  This palsy is a nerve injury at the wrist that causes persistent weakness and clumsiness of the hand and thumb.  Individuals with this condition will notice difficulty with pinching and fine finger movements such as playing the piano or operating a computer keyboard. This condition can result from multi-day road cycling events or a single day of mountain biking.

The muscles most commonly compromised in patients with Cyclists palsy are the First Dorsal Interossei (FDI) and the hypothenar muscles, which are located between the thumb and index finger, and at the inside of the hand, respectively.  Motor supply to these muscles is derived from terminal branches of the Ulnar Nerve. The Ulnar nerve also supplies sensation to a portion of the back of the hand, the little finger and half of the ring finger.  At the wrist, the ulnar nerve enters the hand by passing through Guyons Canal.  This is a tight tunnel that is formed between 2 tiny bones in your wrist (the pisiform and hamate bones) and the ligaments that join these bones together (pisohamate ligament).  Either within or just beyond the canal, the ulnar nerve divides into the motor branches that help move the little finger and thumb respectively. Because the sensory branches of the ulnar nerve are given off before the canal, persistent sensory loss is a rare finding in cyclists palsy.

The reason for the above symptoms is simple.  While cycling, the position of the hands over the handlebars places pressure on the ulnar nerve within Guyons canal. This pressure combined with vibrations from the road or trails is enough to damage the nerve and cause what is called a neuropraxia.  A neuropraxia is a focal injury to a nerve that does not allow for conduction of a nerve impulse past the site of injury.  A loss of the protective nerve coating at the site of injury (demyelination) inhibits the nerve signal and the muscles beyond that point get weak. 

The good news about this type of nerve injury is that it is typically selflimiting, meaning that the nerve will regenerate on its own and function of the muscles will be restored.  A review by Capitani and Beer (2002) found that within 3 months of the onset of symptoms all motor function in the hand was restored to normal if the mechanism of injury was ceased. 
Akuthota et al (2005) found an association between long-distance cycling and delayed nerve impulses along the deep branch of the ulnar nerve.  Nerve damage to the point of neuropraxia was not always evident, but delayed conduction velocity was a consistent finding, demonstrating a significant risk factor with cycling.

Tips to avoid placing excess stress on the Ulnar nerve:

" Wear padded gloves and/or ride with padded handlebars to minimize the vibration forces on your wrist and hands.
" Avoid direct pressure over the area of Guyons canal by distributing your weight evenly across your hands on the handlebars. 
" Have your seat height and position assessed by a professional to make sure it is customized to your body. This will help minimize the amount of weight you place on your wrists.
" Select a proper choice of handlebar. The type of handlebar can also affect the amount of pressure you place through your wrists.
" More specifically for mountain biking, it is important to have good shocks on the front forks of your bike.  They help to absorb and dampen the repetitive vibrations and impact on your wrist while on rough terrain. 

It is important to know about this condition so that you can take steps to avoid it.  Key concepts to remember are:

" Cyclists palsy can be brought on by a single day of mountain biking.
" If symptoms of hand weakness and/or clumsiness develop after a long ride, be sure to seek appropriate medical attention from someone familiar with this type of injury.
" If you develop symptoms, avoid cycling and other positions that place pressure over Guyons canal in order to give the nerve time to recover.
" This condition is self-limiting, so any surgery recommendation before the 3-month recovery period may prolong healing time instead of decreasing it. 

References available upon request.