Don’t lose your nerve with the ulnar nerve: A guide to working up entrapment neuropathies.

Introduction: What is Ulnar Nerve Entrapment? 

Ulnar nerve entrapment neuropathies commonly present to MSK and orthopaedics clinics, with patient’s reporting (pins and needles, paraesthesia, or muscle weakness) that fits a typical distribution. Unpicking the site of compression of the nerve, during a focussed clinical exam, can help clinicians to decide on what work up (imaging, EMG, injection therapy or orthopaedic interventions are needed). We discuss the key clinical tests to use as part of your work, the common imaging findings, and treatment options for ulnar nerve entrapment syndromes.

Getting to grips with the ulnar nerve

Ulnar nerve entrapment is the second most common entrapment neuropathy in the upper limb, (after carpal tunnel syndrome). It commonly occurs at two main anatomical landmarks one at the elbow (cubital tunnel syndrome) and one at the wrist (Guyon’s canal syndrome).

• Cubital tunnel syndrome – has a reported incidence of 30/100,00 (1)
• Incidence of Guyon’s canal syndrome unclear due to lack of population studies.
• Ulnar nerve entrapment neuropathies are reported to be twice as common in middle aged males compared to females (2)

• It has been reported to be common in exercising patients and athletes (cycling, baseball, golfers, weightlifters) and construction workers (24).

Common causes of entrapment neuropathies, include trauma, anatomical variations, functional positions, and compressive lesions.

The Ulnar nerve: Nerve roots and & function 

Spinal roots	C8-T1
Ulnar nerve course	Ulnar nerve arises from the brachial plexus at C8-T1  Travels down the medial aspect of the arm through arcade of struthers  It passes through the cubital tunnel posteriorly to the elbow.  The ulnar nerve penetrates the flexor carpi ulnaris muscle  At the wrist, the ulnar nerve travels superficially to the flexor retinaculum and passes through Guyon’s canal.
Sensory functions	Innervates the medial one and a half fingers and palm area through its three branches; palmar cutaneous branch, dorsal cutaneous branch and superficial branch
Motor functions	Innervates two muscles in anterior forearm: flexor carpi ulnaris and medial half of flexor digitorum profundus  Innervates most of the intrinsic muscles of the hand including: hypothenar muscles, adductor pollicis, palmar and dorsal interossi of the hand, medial two lumbricals

(3)

The anatomy of Cubital tunnel and Guyon’s Canal

• Cubital tunnel: space between posterior and transverse bands of the medial collateral ligament (deep) and Obsbourne’s ligament where the ulnar nerve enters the forearm
• Guyon’s canal: formed by four borders, volar carpal ligament (roof), transverse carpal ligament (floor), hook of hamate (radial border) and pisiform (ulnar border). The canal is further subdivided into three zones, which cause different clinically relevant symptoms (4):
  • Zone 1: dual motor and sensory deficit 
  • Zone 2: isolated motor deficit
  • Zone 3: isolated sensory deficit

The clinical history: working up red flags and common compression sites.

Once red flag conditions have been ruled out (cervical compression, brachial compression, systemic features, and masses). The diagnosis of ulnar nerve entrapment syndromes can be made from 5 S features in the clinical history, alongside the clinical exam.

History

In the clinical history, there are three broad considerations to think about before moving to take a more focussed history. 

1. Does the patient have any red flag features?
   1. Weight loss, night pain, pain unrelated to movement, neck mass, axillary mass, generalised muscle weakness, bilateral symptoms
2. Have I ruled out a more central compression in the neck or brachial plexus?

1. Eg, Thoracic outlet syndrome

3) Have I considered systemic disorders? (5)

1. Eg, neuromuscular disorders eg, ALS

 Take a focussed history using the 5S focused history: 

Examination 

	Guyon’s canal syndrome (5)	Cubital tunnel syndrome
Physical examination	Inspect upper limbs bilaterally: masses, deformity, trauma, muscle wasting and atrophy, claw hand Examine cervical spine, neck and axilla – to rule out thoracic outlet syndrome and cervical root compression Special tests: Allen test, https://www.youtube.com/watch?v=MTqUG4TUeIo  Adson manoeuvre for thoracic outlet syndrome, https://www.youtube.com/watch?v=-7346RaEGKU  Spurling test for cervical nerve root compression https://www.youtube.com/watch?v=3ZSNdv0o0yk
	Inspection/palpation: masses, deformities, pulsatile masses, tenderness over bones	Inspection/palpation: masses, deformities  Determine carrying angle at elbow  Check for ulnar nerve subluxation with elbow flexion/extension
Motor examination	Systematic examination of muscles in the hand Palmar brevis sign (see below) Froment’s test Useful video: https://www.youtube.com/watch?v=mhoIuJVgZUE  Wartenberg’s sign-  Scratch Collapse test- useful tool for diagnosing and localising peripheral nerve compression   https://www.physio-pedia.com/Scratch_Collapse_Test
Sensory examination	Two-point discrimination, light touch and Semmes- Weinstein monofilament testing to delineate sensory loss  Tinel’s sign	Elbow flexion test Provocative test Tinel’s sign Semmes- Weinstein monofilament testing, 2 point and vibratory testing
Vascular examination	Palpate brachial, radial and ulnar pulses, testing for a thrill/bruits, pulsatile pulse Temperature and skin changes in hand- cold, pale fingers indicate arterial insufficiency Allen’s test  Doppler examination may indicated
Differentiators between Guyon’s canal and Cubital tunnel syndrome	Testing sensation over dorsal ulnar aspect of hand– preserved in Guyon’s canal syndrome as the dorsal ulnar cutaneous nerve which innervates this region does not pass through Guyon’s canal (6) Palmar brevis sign– abduction of little finger coincides with palmaris brevis contraction in Guyon’s canal syndrome but not in cubital tunnel syndrome

 

Imaging

MSK Imaging can be considered when there is a suspicion of an underlying compressive lesion. This usually starts with ruling out proximal site before going distal (Cervical Spine > Thoracic outlet > Brachial plexus > Cubital Tunnel  > Guyon’s Canal).

Electrodiagnostic testing

Whilst a suspected diagnosis of ulnar nerve entrapment neuropathies can be made on clinical examination and history, there are some cases where further studies nerve conduction studies (NCS) and electromyogram (EMG) may be useful (7). This is when there is diagnostic uncertainty or where you may need to locate the exact location of the entrapment to aid injection targets or surgical planning. In practical terms this is most important if you need to distinguish between:

1. C8 radiculopathy vs a peripheral ulnar nerve neuropathy

2. Nerve entrapment at the medial epicondyle vs cubital tunnel

3. The level of compression at the Guyon’s canal

Nerve conduction studies (NCS) analyse large myelinated sensory and motor fibres, in controlled conditions. Characteristic changes to summated action potentials of sensory (SNAPs) and motor muscle fibres (CMAPs), can help to determine the site of compression.

 

Key Ultrasound findings of Cubital Tunnel and Guyon’s Canal Entrapment 

Ultrasound is a highly effective tool used for the assessment of ulnar nerve neuropathies, alongside the characterisation of symptoms (5 S approach). It allows for dynamic assessment of nerve morphology, measurements of the affected and unaffected areas of the nerve can be assessed with movement & functional compression. MSK Ultrasound can also uses to deliver diagnostic and therapeutic steroid injections or nerve hydro-disection procedures (9).

 

Ulnar nerve neuropathies can be managed in 3 ways:

Conservative management

Mild symptoms that do not severely impact quality of life can be managed conservatively (splinting & activity modification) (25). Think about the 5S’s history you took for the patient with a particular focus on the ‘Social’ part of the history which considered the occupation and recreational history. Tailored advice, focussed rehabilitation and biomechanics adjustments can be delivered on a case-by-case basis depending on the precipitating and aggravating factors. For example, for a cyclist where you might suspect the cycling as being the causative factor underling their symptoms, you may recommend a change in handlebars or grip to help alleviate symptoms.

Minimally invasive treatments

Minimally invasive treatments involve corticosteroid or dextrose injections which have shown variable efficacy rates in patients. This may depend on the severity of the neuropathy.

Surgical treatment

In cases where conservative or minimally invasive techniques have proven to be ineffective, surgical treatment may be indicated. There are a variety of surgical techniques, which have the unifying aim of nerve decompression, and the two most common interventions are simple decompression and decompression with transposition of the ulnar nerve.

Surgical treatment is recommended in cases where:

• Conservative and non-invasive treatment trials have led to no improvement.

• Serious compression of the ulnar nerve

• Muscle weakness/damage from nerve compression

Surgical outcome tends to be good, but the degree of compression must be considered. In severe compression, (muscle wasting) or loss of nerve function symptoms may remain after surgery. Since nerve recovery is slow, it may take a while to see the surgical outcomes.

The aim of surgical treatment is to relieve pressure on the ulnar nerve so that it is no longer compressed and able to glide freely through the full range of motion.

A review identified no statistically significant difference between simple decompression and transposition surgeries in terms of clinical and neurophysiological improvement, but a higher number of wound infections was associated with transposition surgeries (23). Post-surgical recovery often required splinting for 3-6 weeks alongside a rehabilitation programme.

Surgery to treat ulnar nerve compression at the wrist involves either removing the cause of construction or opening the Guyon’s canal. As with decompression at the cubital tunnel, it may take a while to see the surgical outcome, with possible incomplete recovery in older patients with long-term compression and some muscle wasting/weakness being irreversible.

Conclusion

• Ulnar nerve entrapment commonly occurs at two anatomical landmarks: Guyon’s canal and the Cubital tunnel.

• A detailed clinical history using the 5S framework and the scratch collapse test can be used in clinic to localise an ulnar nerve peripheral neuropathy.

• Nerve conduction studies can help to grade the degree and site of neuropathy.

• Ultrasound features such as – enlarged cross sectional area, dynamic subluxation or evidence of compressive lesions can help to diagnose the condition.

 

Authors

Dr Osama Munajjed

Senior House Officer

Imperial College Healthcare Trust

Miss Geethana Yogarajah

5th year medical student, University of Cambridge

Dr Rifat Hassan

Foundation Year 1 doctor

Norfolk & Norwich University Hospitals

@RifatHassan_

Dr Preena Patel

Consultant Musculoskeletal and Paediatric Radiologist

MSK Lead (Imaging)

Luton & Dunstable University Hospital

Dr Irfan Ahmed

Locum Consultant in Musculoskeletal, Sport & Exercise Medicine, Addenbrooke’s Hospital

Twitter @ExerciseIrfan

Mr Niel Kang

Consultant Trauma & Orthopaedic Surgeon

Cambridge University Hospitals NHS Trust

Affiliate Assistant Professor

Clinical school of medicine, University of Cambridge

Education and Careers Committee

British Orthopaedic Association

Twitter @kangstagram77

No relevant conflicts of interests or relevant disclosures declared by any of the authors.

credit statement: Conceptualization: O.M., G.Y., I.A. and N.K.; Data curation: R.H. and O.M.; Supervision: I.A. and N.K.; MSK imaging: P.P.; Writing – original draft: O.M. and G.Y.; Writing – review & editing: O.M., G.Y., R.H., P.P., I.A. and N.K.

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