Author(s): James B Meiling, DO
Originally published: September 20, 2013 Last updated: April 17, 2025
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Disease/Disorder

Definition

Ulnar mononeuropathy at the wrist (UMW) refers to an injury of the distal portion of the ulnar nerve resulting in motor and/or sensory deficits in its distribution. It is also known as Guyon’s canal syndrome or ulnar tunnel syndrome.1,2 Common causes include external compression by repetitive hand usage, ganglion cysts, or other masses. The clinical presentation is determined by the location of the injury with respect to the branches of the distal ulnar nerve.

Etiology

Distal ulnar nerve injuries may occur due to compression, trauma, or vascular insufficiency.1-3 External compression from repetitive use or volar wrist ganglion cysts are variably cited as the most common causes. Additional causes include lipomas, rheumatoid arthritis (causing synovial cysts or synovial proliferation), tumors, or anomalous anatomical structures (including aberrant hand muscles).2

Epidemiology including risk factors and primary prevention

Epidemiology of UMW is not well-known. Ulnar mononeuropathies are the second most common upper limb entrapment neuropathy, after the median nerve, and the wrist is the second most common entrapment point of the ulnar nerve, after the elbow. Risk factors include occupations, activities, and hobbies that put increased pressure at the base of the palm or wrist. Cycling has been associated with UMW (“Cyclist palsy”). Diabetes has also recently been proposed as a risk factor for ulnar nerve entrapment.4 Primary prevention includes avoiding prolonged pressure at the base of the palm or wrist and the use of padded gloves and/or padded handlebars with cycling. It is also important to ensure adequate fit of any casts, braces, or splints that encompass the wrist to prevent external compression of the ulnar nerve.2

Patho-anatomy/physiology

Guyon’s canal is a tunnel at the wrist between the hook of the hamate and pisiform bones. The floor of the tunnel is formed by the transverse carpal and pisohamate ligaments; the roof by the volar carpal ligament and palmaris brevis muscle.5

In the forearm, the ulnar nerve gives off the palmar cutaneous branch (supplying sensation to the proximal/ulnar palm) and, more distally, the dorsal ulnar cutaneous (DUC) nerve that supplies sensation to the dorsal/ulnar hand. Neither the palmar cutaneous branch nor the DUC nerve traverses Guyon’s canal, and sensation in the distribution of these nerves is spared in UMW.

The ulnar nerve then enters Guyon’s canal where it divides into the deep and superficial branches. The superficial branch supplies sensation to the volar aspects of the 5th and medial half of the 4th digits in addition to the distal/ulnar palmar surface. The only muscle innervated by the superficial branch is the palmaris brevis. In comparison, the deep branch provides a branch to the hypothenar muscles before supplying the interosseous muscles and 3rd and 4th lumbricals. Symptoms of UMW are dependent on the location of the lesion and which nerve branches it affects.

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

Depending on the source, UMW can be divided into 3, 4, or 5 types.  Here, four types will be discussed.1 It should be noted that only Type 1 involves a lesion that is actually in Guyon’s canal.

  • Type 1 involves compression of both the deep and superficial branches of the ulnar nerve.  Compression occurs at the entrance of Guyon’s canal (main trunk of the ulnar nerve) or within Guyon’s canal (both deep and superficial branches).  Both sensation and strength are affected, though the distributions of the palmar cutaneous branch and DUC are spared.
  • Type 2 involves compression only of the deep branch of the ulnar nerve, affecting both the hypothenar branch and the terminal branch to the interossei and lumbricals.  Sensory function is spared.  Compression occurs distal to Guyon’s canal and proximal to the hypothenar branch.
  • Type 3 involves compression of the deep branch distal to the hypothenar branch. The hypothenar muscles are spared, while the interossei and 3rd and 4th lumbricals are affected.  Sensory function is spared as the superficial branch is not involved.
  • Type 4 involves compression of only the superficial branch.  Motor function is spared (with exception of the palmaris brevis muscle). Compression occurs distal to Guyon’s canal. Type 4 is the least common type and is rare.

Compression occurs in the following order of frequency: Type 3 (most common), Type 1, Type 2, Type 4 (least common).

Specific secondary or associated conditions and complications

Complications of untreated UMW may include loss of hand function and an ulnar claw deformity secondary to weakness of the two lumbricals on the thenar side and unopposed action of the medial half of the flexor digitorum profundus (FDP).

Essentials of Assessment

History

History should focus on the distribution of symptoms – especially numbness and weakness, potential risk factors, prior trauma, and exacerbating and alleviating factors. Clinical history suggestive of an ulnar lesion at the elbow (which is a much more common site of ulnar mononeuropathy), such as elbow pain or external compression of the elbow, should also be elicited. The history should also be used to explore mimicking diagnoses, such as a C8-T1 radiculopathy, lower trunk or medial cord brachial plexopathy, or neurogenic thoracic outlet syndrome. In patients with purely motor syndromes, the differential diagnoses should include amyotrophic lateral sclerosis (ALS), monomelic amyotrophy (Hirayama’s disease), multifocal motor neuropathy with conduction block, or distal myopathies. If one of these diagnoses is suspected, the possibility of systemic symptoms and/or symptoms outside the ulnar-innervated distribution should be explored.

Physical examination

Inspection should be performed first, looking for atrophy of the hand intrinsic, abductor digiti mini (ADM), or first dorsal interosseous (FDI) muscle, an ulnar claw hand, or other deformities. Any atrophy of muscles outside the distribution of the ulnar nerve, such as the abductor pollicis brevis (APB), should raise suspicion for alternative/additional diagnoses. Close inspection for fasciculations in ulnar-innervated muscles, as well as other muscles, should be performed.

Manual muscle testing of all major muscle groups should be performed, particularly on hand intrinsic musculature. Ulnar-innervated muscles of the hand may be affected, but ulnar-innervated forearm muscles should be spared – this can help differentiate an ulnar nerve lesion at the wrist from one more proximal at the elbow.

A thorough sensory examination should be performed.  Sensory disturbance of the volar 5th and medial 4th digits may be seen if the superficial branch is affected. Careful attention should be paid to the sensory distributions of the DUC and palmar cutaneous branches of the ulnar nerve.  These branches are spared in UMW but can both be affected in a lesion of the ulnar nerve at the elbow. It should be noted that, in Type 2 and Type 3 lesions, sensation should not be affected. Sensory deficits in the upper limb proximal to the wrist should raise suspicion of a proximal nerve lesion (i.e. plexus, nerve root).

Froment’s sign and Wartenberg’s sign may help identify an ulnar nerve lesion, but these are not specific to UMW. Froment’s sign occurs from weakness of pinch strength between digits 1 and 2 and is due to weakness of the adductor pollicis muscle (innervated by the deep branch of the ulnar nerve). Froment’s sign appears as thumb interphalangeal joint flexion when a patient attempts to grasp a thin object (i.e. piece of paper) between the thumb and index finger, as the median-innervated flexor pollicis longus muscle compensates for a weakened adductor pollicis during this pinching maneuver. Wartenberg’s sign is performed by placing the hand palm down on a flat surface with the fingers extended and passively abducted. The patient is then asked to actively adduct the fingers. Inability to fully adduct the fifth digit is a positive Wartenberg’s sign, indicating weakness in the ulnar-innervated intrinsic hand muscles with unopposed action of the radial-innervated extensor digiti minimi muscle. Palmaris brevis sign may be seen in severe lesions of the deep branch of the ulnar nerve. A positive sign occurs when the 5th digit is abducted and a prominent contraction of the palmaris brevis is seen as a result of atrophic intrinsic hand muscles and sparing of the palmaris brevis muscle.

Functional assessment

The patient’s function must be assessed to determine if the neuropathy is causing impairment of self-care and activities of daily living, including hobbies and recreational pursuits.

Laboratory studies

Laboratory studies are not necessary for the diagnosis of UMW; however, they may help clarify medical status and any underlying etiologies. Certain medications for treating symptoms of pain and paresthesia may warrant investigation of renal or hepatic function.

Imaging

Plain radiographs are of limited utility in the evaluation of UMW unless a history of trauma or underlying pathology (ie rheumatoid arthritis) is considered. Computed tomography (CT) can also identify fractures, especially hamate fractures. Magnetic Resonance Imaging (MRI) or MR Neurogram may suggest ulnar nerve swelling from chronic compression. Alternatively, neuromuscular ultrasound (NMUS) is a painless, non-invasive, and relatively inexpensive imaging technique that can be performed. NMUS of the ulnar nerve may reveal focal enlargement proximal to the site of entrapment, decreased echogenicity, or loss of the normal fascicular pattern, all indicating a focal injury or lesion of the nerve at that site. Doppler can be applied to evaluate for ulnar artery thrombosis. Also, these modalities can identify anomalous anatomic structures (such as an accessory ADM) or other space occupying lesions that may cause compression of the ulnar nerve (such as lipomas or ganglion cysts).5-7

Supplemental assessment tools

The electrodiagnostic evaluation is a key component of the evaluation of UMW.1,8 Needle electromyography (EMG) and nerve conduction studies (NCS) can help localize the lesion, determine the severity and chronicity, and exclude other potential diagnoses in the differential.

  • Sensory NCS should be performed in the distribution of the ulnar and median nerves. It is important to keep in mind that in Type 2 and Type 3 lesions, no sensory abnormalities are expected. In Type 1 and Type 4 lesions, abnormalities in the ulnar sensory NCS to the small finger may include slowing (indicating demyelination in the sensory fibers of the ulnar nerve) or decreased amplitude (indicating axon loss).  The DUC sensory NCS may be useful in differentiating an UMW from a proximal lesion of the ulnar nerve at the elbow.  In a lesion at the wrist, the DUC should be normal, as the DUC branches from the ulnar nerve proximal to the wrist, thereby sparing its involvement in UMW.  In a lesion at the elbow, decreased amplitude or lack of a response may be observed in the DUC.  Decreased amplitude in the DUC and medial antebrachial cutaneous nerves, along with the ulnar sensory NCS to the small finger, may occur in lower trunk or medial cord brachial plexopathies that may mimic the symptoms of an ulnar mononeuropathy.
  • Motor NCS should be performed when stimulating the ulnar nerve and recording over the FDI and ADM muscles.  In Type 3 lesions, distal latency and amplitude should be normal while recording at ADM, while recording at FDI would be expected to show abnormalities.  Particularly when recording at FDI, comparison to the contralateral (unaffected) limb may be useful to identify abnormalities. In Type 1 and Type 2 lesions, abnormalities may be seen in the distal latencies and amplitudes when recording at both ADM and FDI. In Type 4 lesions, no abnormalities are expected in motor NCS. Stimulation of the ulnar nerve in the palm may help identify conduction block caused by demyelination in the ulnar nerve in the wrist. Careful attention should be paid to the conduction velocity in the ulnar nerve in the across-elbow segment to exclude the possibility of an ulnar mononeuropathy at the elbow.  Median motor NCS are also an important part of the examination. Simultaneous abnormalities in both median and ulnar motor NCS should raise suspicion for a systemic polyneuropathy, motor neuron disease, lower trunk or medial cord brachial plexopathy, or C8-T1 radiculopathy.
  • Short segment incremental studies (“inching”) of the ulnar nerve in the wrist region may be useful to identify a point of focal slowing in the ulnar nerve.
  • EMG should be performed in ulnar-innervated intrinsic hand muscles (including FDI and ADM) as well as median-innervated hand muscles (including APB and/or opponens pollicis).  Proximal ulnar-innervated muscles, such as the FDP to digits 4 and 5 and flexor carpi ulnaris, should be sampled to exclude a proximal ulnar mononeuropathy, although normal findings in these muscles do not rule out an ulnar mononeuropathy at the elbow. In cases of a non-localizable ulnar mononeuropathy, NMUS should be employed as an adjunct to the electrodiagnostic study to look for anatomic changes of the nerve throughout its course.9 Denervation in the FDI with sparing of the ADM should raise suspicion for a Type 3 lesion, while a Type 1 or Type 2 lesion would be expected to affect both muscles.  Denervation in the APB, opponens pollicis, flexor carpi ulnaris, or FDP should not occur in UMW and should result in consideration of alternative diagnoses.  Motor neuron disease, such as ALS or monomelic amyotrophy, would be expected to result in widespread or diffuse denervation as well as prominent fasciculations. A distal myopathy would be expected to result in early recruitment of small motor unit potentials.

Rehabilitation Management and Treatments

Available or current treatment guidelines

Treatment is based, first, on obtaining a correct diagnosis, and second, on identifying the underlying cause. Treatment should be aimed at alleviating the underlying cause and treating any associated symptoms. According to the European HANDGUIDE study,10,11 recommended treatment options include activity modification, splinting, and surgery. Mild symptoms may be treated conservatively with activity modification, occupational / hand therapy, or splinting. More severe symptoms, especially those functionally limiting the patient such as progressive weakness, severe numbness, and deformity, should be referred to a hand surgeon for surgical evaluation.

At different disease stages

New onset/acute

Most experts have recommended activity modification with a combination of patient instructions and splinting in the setting of acute/subacute and mild symptoms. The patient should be advised to minimize pressure to the wrist and base of the palm, which can be done with a properly fitted neutral wrist splint or by simply avoiding pressure and mechanical overload to the area. Occupational / hand therapy may be beneficial to help maintain muscle strength and assist with occupational accommodations. Cyclists with UMW should be encouraged to use padded gloves, padded handlebars, and/or modify their grip. Medications, such as nonsteroidal anti-inflammatories, tricyclics, opioids, and anticonvulsants, are also frequently used to help minimize symptoms, although experts have agreed that they have not proven useful in treatment. Surgical decompression to relieve pressure on the ulnar nerve can be an option for severe cases.

Chronic/progressive

If weakness and symptoms progress, then surgical decompression should be considered. Ulnar tunnel release has produced particularly successful outcomes in ulnar tunnel syndrome resulting from trauma or aberrant muscles.

Coordination of care

Care of a patient with UMW may involve a primary care provider, physiatrist, electromyographer, occupational / hand therapist, and hand surgeon. Coordinating care with clear treatment goals is important for appropriate management of this issue.

Patient & family education

Patients should be educated on signs and symptoms of UMW, the basic anatomy, and pathophysiology. Especially when patients are treated conservatively, it is important to educate the patient on signs that the lesion is progressing, such as worsening numbness, weakness, hand muscle atrophy, and/or hand deformity.  Education regarding activity modifications is important to attempt to avoid progression.

Cutting Edge/Emerging and Unique Concepts and Practice

Corticosteroids are occasionally injected into the area of entrapment to help reduce pain and inflammation. Unlike injections for carpal tunnel syndrome, there is a lack of evidence demonstrating benefit to this intervention in the available literature. Ultrasound-guidance may be a feasible option for improved accuracy for steroid injections, nerve blocks, and/or hydrodissection for UMW.7,12

Gaps in the Evidence-Based Knowledge

There is some controversy on the types of UMW, with various authors suggesting as few as 3 and as many as 5 types.1,3 These types are described based on their clinical and electrodiagnostic characteristics and refer to the location of entrapment within Guyon’s canal. When evaluating a patient, it is important to describe the clinical findings and perform the electrodiagnostic evaluation in sufficient detail to identify the entrapment point in the canal. Due to a lack of large-scale trials, comprehensive guidelines regarding diagnosis and management of UMW have not been well established. There is also limited data on the success of conservative measures to treat UMW.

References

  1. Stewart, J., Focal Peripheral Neuropathies. 2010 West Vancouver, Canada: JBJ Publishing.
  2. Chen, S.H., et al. Ulnar tunnel syndrome. J Hand Surg Am. 2014; 39(3): p. 571-9.
  3. Donofrio, P., Textbook of Peripheral Neuropathy. 2012, New York, NY: Demos Medical.
  4. Rydberg, M., et al., Diabetic hand: prevalence and incidence of diabetic hand problems using data from 1.1 million inhabitants in southern Sweden. BMJ Open Diabetes Res Care, 2022. 10(1).
  5. Saran, S., et al. Unveiling Guyon’s canal: insights into clinical anatomy, pathology, and imaging. Diagnostics (Basel). 2025; 15(5): p. 592.
  6. Cartwright, M.S., et al. Neuromuscular ultrasound in common entrapment neuropathies. Muscle Nerve. 2013; 48(5): p. 696-704.
  7. Wu, W.T., et al. Ultrasound imaging and guidance for distal peripheral nerve pathologies at the wrist/hand. Diagnostics (Basel). 2023; 13(11): p. 1928.
  8. Preston, D.C., et al. Electromyography and Neuromuscular Disorders: Clinical-Electrophysologic-Ultrasound Correlations. 2020, Philadelphia, PA: Elsevier.
  9. Alrajeh, M., et al. Neuromuscular ultrasound in electrically non-localizable ulnar neuropathy. Muscle Nerve. 2018; 58(5): p. 655-9.
  10. Hoogvliet, P., et al., How to treat Guyon’s canal syndrome? Results from the European HANDGUIDE study: a multidisciplinary treatment guideline. Br J Sports Med, 2013. 47(17): p. 1063-70.
  11. Li, C-W., et al., Prospective outcome analysis of ulnar tunnel syndrome: Comparing traumatic versus non-traumatic etiologies. Asian J Surg, 2023; 46(1): p. 180-6.
  12. Meng, S., et al. Ultrasound-guided perineural injection at Guyon’s tunnel: an anatomic feasibility study. Ultrasound Med Biol. 2015; 41(8): p. 2119-24.

Original Version of the Topic

Bradeigh S. Godfrey, DO. Ulnar nerve mononeuropathy at the wrist. 9/20/2013

Previous Revision(s) of the Topic

Kevin Fitzpatrick, MD. Ulnar nerve mononeuropathy at the wrist. 2/13/2018

Thomas Chai, MD, Eliana Ege, MD. Ulnar Mononeuropathy at the Wrist. 6/23/2022

Author Disclosures

James B Meiling, DO
Nothing to Disclose