When a client comes in complaining of pain, numbness/paresthesia or weakness in the hand, it is likely that carpal tunnel syndrome (CTS) is what comes to mind first. Yet, there is another fibro-osseous tunnel in the wrist where nerve compression occurs, called Guyon's canal or Guyon's tunnel. The ulnar nerve travels through this tunnel and is susceptible to compression here.

There are some key factors to understand about the anatomical arrangement of structures in Guyon's canal that govern the most effective treatments. The first place to begin is with a solid understanding of the anatomical structure of Guyon's canal. Treating compression in this canal differs from treating median nerve pathology (CTS).

Anatomical Arrangement

The flexor retinaculum, also called the transverse carpal ligament, traverses the base of the hand between the pisiform and hamate on the ulnar side and the scaphoid and trapezium on the radial side. Some anatomy textbooks don't show it, but the flexor retinaculum actually splits into two divisions toward the ulnar side of the hand. There is a broad, deep band and a superficial short band. The space between these two bands is Guyon's canal (Figure 1).

The ulnar nerve artery and vein pass through this canal. Unlike the carpal tunnel which houses numerous tendons, there are no tendons traveling through Guyon's canal. The lack of tendons in the tunnel plays a prominent role in distinguishing ulnar nerve pathology from median nerve pathology.

Guyon's Canal Syndrome

In CTS, structures within the carpal tunnel, such as the flexor tendons, become inflamed and compress the median nerve. Because median nerve compression results from structures within the tunnel, the focus of treatment is on reducing inflammation and compression from these intrinsic (within the tunnel) structures.

In Guyon's canal syndrome (GCS) the only structures within the tunnel are the ulnar nerve, artery and vein, so nerve compression in this condition does not result from intrinsic factors but from those outside the tunnel (extrinsic factors). The nerve compression experienced in GCS is most likely associated with activities where there is either excessive pressure on the base of the hand or pressure applied to the region for prolonged periods.

This condition is frequently referred to as handlebar palsy because of the frequency with which it occurs in long distance cyclists who have their hyperextended wrist pressing on the handlebars and absorbing road vibration. Another common reason for GCS is walking with a cane where body weight pressure is put on the cane handle right over the ulnar nerve in the canal. Falling on an outstretched hand or hitting something hard with the base of the hand can also produce an acute onset of GCS.

The key difference between these situations and that of carpal tunnel syndrome is that in each of the ulnar nerve compression situations, pressure is placed on the base of the hand by some external factor, not compression from within the tunnel. The fact that these causes are all from extrinsic and not intrinsic compression is important when constructing appropriate treatments.

Assessment

The client with Guyon's canal syndrome may present with both sensory and motor symptoms. Sensory symptoms include pain, paresthesia or numbness in the ulnar nerve distribution of the hand (Figure 2). Motor symptoms include weakness or atrophy in the hypothenar muscles at the base of the hand or in the adductor pollicis muscle of the thumb. The motor symptoms of weakness or atrophy are the most common presentation with this condition.

Visual observation of the base of the hand often reveals an indication of ulnar nerve compression. If there is significant atrophy of the hypothenar muscles, they will appear far less developed than the unaffected side (the other thumb) if there isn't bilateral nerve compression.

The adductor pollicis muscle plays a key role in evaluation of this pathology with a simple orthopedic test called Froment's sign (Figure 3). Have your client hold a thick piece of paper or business card between the thumb and index finger with the fingers folded in as shown in the picture. Instruct the client to hold the paper firmly as you attempt to pull the paper from the client's grip. If you are able to easily pull the paper from the client's grip, it is likely that there is significant weakness in the adductor pollicis muscle and ulnar nerve pathology is likely to blame.

Treatment Strategies

The most important strategies in treatment involve removing any factors that are compressing the nerve and giving the nerve proper time to heal. The client interview is key for determining what the precipitating factors are. Find out what the client's activities are or were that lead up to the symptoms and ask about any changes (use of a cane for example) in their behavior or lifestyle. The reasons for the compression problems are not always obvious, so ask more questions if the symptoms fit the condition but the activities don't initially.

In any nerve compression pathology, the primary goal of treatment is to reduce pressure on the affected nerve. This goal is the same for Guyon's canal syndrome. However, because the primary cause of nerve compression is extrinsic, massage techniques should not be applied directly to this area as they could cause further compression of the nerve and prolong the pathology.

Massage treatment in other portions of the upper extremity can, however, provide significant benefit. Much has been written in recent years about the key benefits of neural mobility.1 Therefore, working all of the tissues along the path of the ulnar nerve will enhance full neural mobility and give the nerve the best possible environment for healing, which sometimes is lengthy with nerve conditions.

Without knowing and understanding some of these key facets of Guyon's canal syndrome, the practitioner may inadvertently aggravate a nerve compression problem by attempting to work around the wrist and hand for someone experiencing hand pain or weakness. This is a valuable reminder that while massage is highly beneficial in most cases, there are instances in which our intervention could be problematic or cause a condition to get worse if we apply it inappropriately.

References:

1. Shacklock M. Clinical Neurodynamics. Edinburgh: Elsevier; 2005.