Guyon’s Canal Syndrome

Introduction: The median nerve travels through a soft-tissue tunnel at the base of the hand. Nerve entrapment within the tunnel constitutes the most common upper extremity nerve entrapment, which we all know as carpal tunnel syndrome(CTS). People experiencing neurological symptoms in the hand often immediately suspect CTS as the cause. However, the median nerve is not the only one affected in the wrist, and is also not the only nerve that travels through a soft-tissue tunnel at the base of the hand. The ulnar nerve also courses through a soft-tissue tunnel at the base of the hand, known as Guyon’s canal, or Guyon’s tunnel. Compression of the ulnar nerve within this tunnel is known as Guyon’s canal (or tunnel) syndrome. It is far less common than CTS, but an important condition to be aware of with nerve pain in the upper extremity.

Anatomical Background

Guyon’s canal is created by a series of stabilizing ligaments and connective tissues of the wrist and hand. The flexor retinaculum, also called the transverse carpal ligament, makes up the roof of the carpal tunnel (Image 1). This same connective tissue structure makes up the floor of Guyon’s canal, so this tunnel is actually superficial to the carpal tunnel on the ulnar aspect of the wrist.

Image 1
Flexor retinaculum as roof of carpal tunnel and floor of Guyon’s canal
Image is from 3D4Medical’s Complete Anatomy application

The connective tissues of the wrist and base of the hand blend together in a complex webbing. As a result it is difficult to separate and distinguish the exact boundaries of some of these connective tissues, which is the likely reason for the discrepancy in identifying the upper margin or roof of Guyon’s canal. Some sources say the roof of the canal is created by the palmar carpal ligament (Image 2);¹ others say it is created by a connective tissue expansion of the flexor carpi ulnaris tendon.² Important to note is that the transverse carpal ligament is at the base of the tunnel and there is a connective tissue band across the top that may extend from several tissues. Regardless of which tissue the tunnel roof originates from, it provides the upper boundary for the tunnel.

Image 2
Palmar carpal ligament as roof of Guyon’s canal
Image is from 3D4Medical’s Complete Anatomy application

A key difference between the carpal tunnel and Guyon’s canal is the absence of tendons in Guyon’s tunnel. There are nine tendons that run through the carpal tunnel along with the median nerve. Because there are so many structures going through the tunnel, nerve compression can occur from inflammation and overuse of the tendons and their surrounding synovial sheaths. The situation is quite different in Guyon’s canal. There are no tendons that run through Guyon’s canal, so nerve compression in this condition does not occur from inflammatory tenosynovitis or pressure from aggravated tendons. The contents of Guyon’s canal are the ulnar nerve, artery and veins. The majority of problems that occur in Guyon’s canal syndrome arise from external compressive forces at the base of the hand. That means nerve compression generally results from external pressure on the hand instead of internal pressure generated inside the tunnel.

There are specific aspects of neural anatomy that are important to understand for identifying the key symptom patterns in Guyon’s canal syndrome. Prior to entering the canal the ulnar nerve divides into the superficial and deep branches (Image 3). The superficial branch is primarily sensory although it does carry a significant number of motor fibers as well. The deep branch carries primarily motor fibers. As a result, compression of the superficial branch usually produces mixed motor and sensory symptoms, while compression of the deep branch generally produces motor impairment with very few sensory symptoms.

Image 3
Distal branches of ulnar nerve
Image is from 3D4Medical’s Complete Anatomy application

Clarifying Guyon’s Canal Syndrome

Guyon’s canal syndrome is classified according to where the compression occurs. The original and most common classification was published in a paper by Shea and McClain in 1969.³ They describe three types of ulnar nerve compression (Image 4). Type I involves compression prior to the separation of the deep and superficial branches. Because this location includes fibers from both the deep and superficial branches, the symptoms include a mix of motor and sensory impairment. Type II involves compression of the deep motor branch after it has separated from the superficial branch. Because the deep motor branch contains almost exclusively motor fibers, the primary symptoms from compression in the Type II version are atrophy and weakness in thumb and hand muscles.

Image 4
Three locations of compression for ulnar nerve branches
Image is from 3D4Medical’s Complete Anatomy application

The adductor pollicis is one of the larger muscles supplied by this deep branch of the ulnar nerve. Weakness or atrophy in this muscle may be apparent by a decreased size or hollowing out of the thenar aspect of the palm. Muscle weakness in the adductor pollicis can also be tested with the Froment’s sign that is described later in this article. Compression of motor fibers in the Type II version is the most common of these three variations. Therefore, it is more common to see patterns including muscle weakness with a lesser degree of sensory symptoms for most cases of Guyon’s canal syndrome.

Type III compression occurs near the distal end of the canal and affects the superficial sensory branch, and symptoms are generally paresthesia, numbness, or sharp pain sensations in the ulnar aspect of the hand or the last two fingers.

Clients may complain of neurological sensations throughout the entire hand. Mechanical factors that lead to median nerve compression in CTS may also affect the ulnar nerve in Guyon’s canal. In these cases neurological sensations are felt throughout the entire palmar aspect of the hand.⁴ If symptoms are being felt in both the median and ulnar nerve distributions of the hand, it is important to address potential entrapment locations of both the median and ulnar nerves.

What Causes Guyon’s Canal Syndrome

Median nerve compression in carpal tunnel syndrome is often created by inflammation of structures within the tunnel and the majority of cases involve intrinsic (compression from within the tunnel) pressure. The majority of Guyon’s canal syndrome cases appear to occur from extrinsic (outside the tunnel) compression, although anatomical factors can produce compression from within the tunnel itself.

Soft-tissue cysts or tumors can develop inside the canal and are one of the more common factors of intrinsic compression. There are also reports of anatomical anomalies such as unusual muscles or tendons that can occur within the tunnel.⁵ Hypertrophy or enlargement of the flexor carpi ulnaris muscle can also cause a decrease in tunnel volume, as can irregularities in the shape of the hook of the hamate bone. It is difficult to identify any of these anatomical anomalies through physical examination and most are identified through high-tech diagnostic studies or surgical exploration. From a clinical perspective recognizing the possible existence of anatomical anomalies helps narrow the assessment when no apparent signs indicate a likely cause for nerve compression.

The most common causes of Guyon’s canal syndrome involve external pressure on the base of the hand that compress the nerve. If the wrist is in hyperextension when a compressive force is applied to the base of the hand, the nerve is at risk of injury because the nerve is stretched and exposed in this position. The FOOSH (Fall On Outstretched Hand) injury is an example, as the person’s body weight lands on the base of the hand with the wrist in full hyperextension. This position makes the ulnar nerve vulnerable to compression injury. The ulnar nerve can also be injured by bone displacements or fractures in the wrist that occurred during the FOOSH.

Guyon’s canal syndrome is common among long-distance cyclists because their body position places upper body weight onto a hyperextended hand holding the bike’s handlebars. Within the cycling community this condition is frequently referred to as handlebar palsy. It is especially aggravated with long periods of downhill riding when more pressure is put on the hands.

A comparison of FOOSH injury and handlebar palsy illustrates the differences in degree of nerve injury in this condition. The degree of nerve compression is related to 1) the amount of compressive force and 2) the length of time that force is applied. In the FOOSH injury there is a high degree of compressive force, but the force is applied only for a short time. In handlebar palsy the compressive force is much less, but the force is applied over a longer period.

The practitioner should identify key factors in the client history that indicates both the amount of compressive force applied and the length of time it was applied in order to determine the severity of nerve compression. Other factors that lead to Guyon’s canal syndrome include walking on crutches, operating power tools, and various sporting activities such as handball, basketball, tennis, squash, golf, martial arts, and breakdancing.

Another cause of the ulnar nerve compression of the wrist is sometimes described in the literature as hypothenar hammer syndrome. This is essentially a fancy name for banging something with your hand. We would all be wise to remember that the hand is not a hammer and using it like one can easily lead to nerve compression.

Assessment and Evaluation

Recognizing clinical signs and symptoms along with a detailed physical examination remains the most accurate means of assessing ulnar nerve compression in the canal. In addition to the information reported during the client history (pain in the hand, weakened grip strength, history of wrist compression, etc.), there are other key clinical indicators. During range of motion testing at the wrist, pain or neurological symptoms are usually exaggerated by wrist extension movements as this will bowstring the nerve within the tunnel. However, keep in mind that the Type II compression primarily affects motor fibers, so the sensory symptoms would not show up during a Type II compression problem, which is the most common.

Image 5
Atrophy of hand muscles (flatness of palm) from ulnar nerve compression
Image courtesy of Wikimedia Commons

As noted earlier, hypothenar or thenar muscle atrophy may be visible (Image 5). There may also be some lack of coordination in specific hand movements or grasping activities which can be tested during physical examination. Sometimes clawing of the hand may be apparent (Image 6). If atrophy is visible in the hand, it usually indicates a chronic condition as atrophy does not occur rapidly.

Image 6
Clawing of the hand sometimes present in Guyon’s canal syndrome
Image courtesy of Wikimedia Commons

When performing the physical examination keep in mind that other locations of ulnar nerve entrapment can occur throughout the upper extremity and may give similar symptoms. In fact, ulnar nerve compression in the cubital tunnel at the elbow is actually the second most common upper extremity nerve entrapment condition. Compression of the early branches of the ulnar nerve are also far more common in thoracic outlet syndrome than Guyon’s canal syndrome, so screen for this possibility as well.  It’s important to identify any more proximal location of nerve entrapment and treat the entire length of the ulnar nerve so that all potential locations of nerve compromise can be addressed. This will decrease the likelihood that multiple nerve compression sites (called multiple crush phenomenon) will cause additional nerve impairment.

A special orthopedic test called Tinel’s sign is sometimes used to identify ulnar nerve compression at the wrist. This test is performed by tapping on the potential area of nerve compression with the fingertips and evaluating if it produces increased neurological sensation. Tinel’s sign is only helpful for the Type I and III versions of Guyon’s canal syndrome since those have predominant sensory symptoms. The Tinel’s sign is not considered highly accurate to begin with and since the Type II (motor nerve variation) of Guyon’s canal syndrome is more common, Tinel’s sign is not used with great frequency to evaluate this problem.

Another orthopedic test called Froment’s sign focuses on the Type II (motor) variation. In this test the client grasps a small piece of paper between the thumb and fingers. The practitioner attempts to pull the paper out of the client’s grasp (Image 7). If it is hard to pull the paper out, this indicates a strong and well-functioning adductor pollicis muscle. If it is easy to pull the paper out, this generally indicates weakness in the adductor pollicis muscle, which is innervated by the ulnar nerve and may indicate compression of that motor branch.

Image 7
Froment’s sign for evaluating muscle weakness

Treatment Strategies

With nerve compression problems the primary strategy is to decrease pressure on the nerve so that it can heal. Because so many cases of Guyon’s canal syndrome involve external compression, a primary treatment goal is to adjust lifestyle activities (like biking ergonomics) to decrease pressure on the base of the hand. Nerve tissue is slow to heal so it can take a matter of months for symptoms to abate depending on how severe the nerve compression was to begin with.

Because treatment should avoid putting additional pressure on the nerve, massage treatment should be applied carefully in this region so as not to further aggravate nerve compression. Treatment of any ulnar nerve compression problem will be most effective if the entire pathway of the nerve can be addressed throughout the upper extremity. That means specific attention should be focused to the medial aspect of the forearm and upper arm.

In addition, treatment strategies that reduce hypertonicity in the pectoralis minor muscle and lateral cervical muscles where the brachial plexus branches exit the thoracic outlet will be particularly helpful. Any number of massage techniques could be helpful in this region as long as they are aimed at reducing muscular hypertonicity and not putting additional pressure on vulnerable compression sites of the nerve.

Some clients will not respond to massage or other conservative treatment interventions. There may be an obstruction in the canal that cannot be addressed through noninvasive procedures and surgery is a likely option. However, a thorough regimen of conservative treatment(s) prior to surgery is always recommended to reduce issues that could further impair the function of the nerve. Greater awareness of less frequently occurring conditions such as Guyon’s canal syndrome helps us deliver more effective treatment for our clients.

1. Brody MJ, Bindra RR. Ulnar tunnel syndrome. Disord Hand Vol 2 Hand Reconstr Nerve Compression. 2015;43(4):267-282. doi:10.1007/978-1-4471-6560-6_15.
2. Pecina M, Markiewitz A, Krmpotic-Nemanic J. Tunnel Syndromes: Peripheral Nerve Compression Syndromes. Boca Raton: CRC Press; 2001.
3. Shea J, McClain E. Ulnar-nerve compression syndromes at and below the wrist. J Bone Jt Surg Am. 1969;51(6):1095-1103.
4. Lewańska M, Walusiak-skorupa J. Is Ulnar Nerve Entrapment At Wrist Frequent Among Patients With Carpal Tunnel Syndrome Occupationally Exposed To Monotype Wrist Movements ? 2017;30(6):861-874.
5. Hoogvliet P, Coert JH, Fridén J, Huisstede BMA. How to treat Guyon’s canal syndrome? Results from the European HANDGUIDE study: A multidisciplinary treatment guideline. Br J Sports Med. 2013;47(17):1063-1070. doi:10.1136/bjsports-2013-092280.