Cubital Tunnel Syndrome

                                  Dr. KS Dhillon

Introduction

Cubital tunnel syndrome is neuropathy of the ulnar nerve which causes symptoms of numbness and shooting pain along the medial aspect of the forearm and medial half of the fourth digit and the fifth digit. Compression or irritation of the ulnar nerve at the elbow region causes it.

Ulnar Nerve Anatomy

The C8 and T1 nerve roots join and give rise to the medial cord of the brachial plexus. The ulnar nerve originates as a branch of the medial cord. 

The ulnar nerve along with the brachial artery then travels down the arm towards the elbow joint.  At the middle of the arm, the ulna nerve enters the posterior compartment by piercing the intermuscular septum (arcade of Struthers). It then travels along the medial aspect of the triceps to enter the cubital tunnel. In the cubital tunnel, the ulnar nerve travels between the olecranon and the medial epicondyle beneath the Osborne ligament. After the ulna nerve exits the cubital tunnel, it passes under the aponeurotic head of flexor carpi ulnaris to enter the forearm. The cubital tunnel is where the ulnar nerve is most likely to be compressed due to its location and anatomy. The nerve can also get compressed at the arcade of Struthers or by the aponeurotic head of flexor carpi ulnaris. The ulnar nerve innervates the medial side of the forearm, the ulna side of the palm, the little finger, and the ulna half of the ring finger. The ulna nerve supplies motor branches to flexor carpi ulnaris, flexor profundus of the little and ring fingers, hypothenar muscles, adductor pollicis brevis, all the interossei, and the third and fourth lumbricals. 

Etiology

There are several causes of ulnar nerve compression at the cubital tunnel that can cause symptoms such as tingling along the medial aspect of the forearm, the little finger, and the medial aspect of the ring finger.

Pressure on the ulnar nerve is the most common cause of these symptoms. The ulnar nerve is quite superficial at the medial epicondyle region. This is why people may experience the feeling of shooting pain and electric shock in the forearm if they accidentally hit the elbow on a hard surface.

Stretching the ulnar nerve can also produce similar symptoms. During elbow flexion, the ulnar nerve can get stretched because of its anatomical position. Repetitive elbow flexion and extension can cause damage and irritation to the ulnar nerve. Some individuals sleep with elbows flexed. This can stretch the ulnar nerve for an extended period during sleep and cause irritation to the ulnar nerve.

Injuries to the elbow joint leading to fractures, dislocations, swelling, and effusions can cause anatomical damage which will cause symptoms because of compression/irritation of the ulnar nerve.

A study of 117 patients by Omejec and Podnar (1) identified that direct pressure on the nerve because of habits while sitting, or secondary to occupational activities is a significant cause of nerve damage as the nerve passes posterior to the medial epicondyle.

Epidemiology

After carpal tunnel syndrome, ulnar nerve neuropathy is the second most common compression neuropathy of the arm. Filippou et al (2) studied 91 patients and they found that nearly 60% of the patients had anatomical changes in the cubital tunnel that caused the ulnar nerve neuropathy, of which nearly 20% had a subluxation of the ulnar nerve. There were osteophytes in almost 7% of patients and luxation of the ulnar nerve in nearly 10% of the patients. Trauma also can cause symptoms in about 3.3% of patients (2).

Pathophysiology

The exact pathophysiology of the cubital tunnel syndrome is not known. Smoking is a risk factor for cubital tunnel syndrome (3). It is more common in males. The left side is more often affected (4).

History and Physical Examination

The patient typically presents with complaints of "pins and needles" in the forearm and the hand. The tingling sensation is usually present along the little finger and medial half of the ring finger. The symptoms are usually aggravated with elbow flexion. These symptoms are usually transient initially then gradually get worse. 

Examination may show reduced or complete loss of sensation on the palmar and dorsal aspects of the little finger and the medial part of the ring finger (5,6). Tinel's sign is usually positive along the cubital tunnel. Provocative tests like sustained elbow flexion for one minute or compression of the ulnar nerve at the cubital tunnel region may be positive, causing paresthesia along with the distribution of the ulnar nerve. The diagnostic value of these tests is however poor (7). In some patients, the ulnar nerve may subluxate over the medial epicondyle with elbow flexion.

Motor symptoms are uncommon and usually manifest in severe cases of ulnar neuropathy. Patients may complain of weakness in the hand. They frequently drop objects. Findings on examination could range from mild weakness of the interosseous muscles to severe atrophy of the hand intrinsics muscles and weakness of the handgrip. Froment's sign can be positive. It indicates weakness of the adductor pollicis, which is supplied by the ulnar nerve. Ulnar claw hand is unlikely in patients with cubital tunnel syndrome because the flexor digitorum profundus to the ring and little fingers is also denervated.

Evaluation

In evaluating patients with ulnar neuropathy a thorough knowledge of the motor and sensory distribution of the ulnar nerve is critical. Diagnosis can be made clinically. Nerve conduction studies are quite often used to confirm the diagnosis. In some patients, however, in the early stages of symptoms, the nerve conduction may be normal. Interpretation of nerve conduction studies should always be in a clinical context.

X-rays of the elbow joint can be done to exclude bony pathologies which may cause compression of the nerve (8).

Ultrasonic scanning (USS) and magnetic resonance imaging (MRI) have a sensitivity and specificity of over 80% in diagnosis. MRI and USS can also help to identify other causes of compression, which may not be picked up on plain radiographs such as soft tissue swelling and lesions such as ganglions, neuroma, and aneurysms (9).

Management

When deciding on treatment options, pathological findings should undergo careful evaluation. Often patients can benefit from non-surgical treatment. The clinician should, therefore, evaluate and determine an end goal of treatment with the patient before deciding on the method of treatment.

Non-surgical Treatment

In patients whose symptoms are due to mechanical factors such as leaning over the desk at work with weight on the elbows or sleeping with bent elbows, correcting these postures that provoke ulnar neuropathy can be the mainstay of treatment.

Padua et al (10) in an Italian study followed up 24 patients who had willingly declined surgery after the initial diagnosis. About half of their patients reported improvement in their symptoms during follow-up. Their further nerve conduction studies also showed improvement. This further supports the evidence that patients with mild symptoms can be managed without surgery (10).

Night-time splinting to keep the elbows straight has been suggested as an initial management option in patients with mild symptoms (6). Analgesics such as NSAIDs will help to relieve the pain.

Surgical Treatment

Patients with severe symptoms and signs such as atrophy of interossei and weakness of the hand grip might not improve with conservative treatment. Patients who have failed conservative treatment for 6 months would also require surgical intervention. Surgical treatment involves decompression of the nerve throughout the entire cubital tunnel. Some doctors release the pressure in the cubital tunnel region. Other doctors prefer free mobilization of the ulnar nerve. 

There are various methods of surgical treatment. Some of the well accepted surgical procedures include:

1) in-situ decompression

2) endoscopic decompression

3) decompression followed by subsequent subcutaneous transposition, intramuscular transposition, or submuscular transposition

4) medial epicondylectomy along with in-situ decompression (6)

In terms of clinical outcome, studies have shown no benefit of one over the other (11).

Differential Diagnosis

The differential diagnosis includes:

• Brachial plexus injuries

• Thoracic outlet syndrome

• Syringomyelia

• Lesions in the Guyon (ulnar) canal

• Cervical spondylosis

• Pancoast tumors

• Motor neuron disease

• Carpal tunnel syndrome

• Polyneuropathy

Prognosis

The symptoms improve with conservative treatment in about half of the patients (5).

Complications

After surgical decompression one in eight patients may find that their symptoms recur (12). Inadequate decompression is the most frequent cause of revision surgery. Recovery can be slow and incomplete. In some patients, symptoms may worsen before they improve.

Injury to the medial antebrachial cutaneous nerve of the forearm is a common complication following cubital tunnel release and can be painful (13).

Postoperative Care

A full range of motion of the elbow is usually allowed following surgical intervention. Usually, post-operative physical therapy is not required unless there is significant muscle weakness. Patients are allowed to return to light work in 3 to 4 weeks.

Conclusion

Ulnar nerve neuropathy can be due to several causes. Differential diagnosis have to be kept in mind while evaluating patients with ulnar neuropathy.  A thorough knowledge of the sensory and motor distribution of the ulnar nerve is critical in evaluating patients with ulnar neuropathy and identifying the site of pathology.

Input by an interprofessional team including a nurse, physical therapist, and doctor can enhance recovery. Physiotherapy can be useful if muscle weakness is present. The doctor should discuss the surgical approach and the potential risks/benefits of the procedure with the patient. 

References

1. Omejec G, Podnar S. What causes ulnar neuropathy at the elbow? Clin Neurophysiol. 2016 Jan;127(1):919-924.

2. Filippou G, Mondelli M, Greco G, Bertoldi I, Frediani B, Galeazzi M, Giannini F. Ulnar neuropathy at the elbow: how frequent is the idiopathic form? An ultrasonographic study in a cohort of patients. Clin Exp Rheumatol. 2010 Jan-Feb;28(1):63-7.

3. Frost P, Johnsen B, Fuglsang-Frederiksen A, Svendsen SW. Lifestyle risk factors for ulnar neuropathy and ulnar neuropathy-like symptoms. Muscle Nerve. 2013 Oct;48(4):507-15.

4. Kanat A, Balik MS, Kirbas S, Ozdemir B, Koksal V, Yazar U, Kazdal H, Kalaycioglu A. Paradox in the cubital tunnel syndrome--frequent involvement of left elbow: first report. Acta Neurochir (Wien). 2014 Jan;156(1):165-8.

5. Wojewnik B, Bindra R. Cubital tunnel syndrome - Review of current literature on causes, diagnosis and treatment. J Hand Microsurg. 2009 Dec;1(2):76-81. 

6. Assmus H, Antoniadis G, Bischoff C. Carpal and cubital tunnel and other, rarer nerve compression syndromes. Dtsch Arztebl Int. 2015 Jan 05;112(1-2):14-25; quiz 26.

7. Beekman R, Schreuder AH, Rozeman CA, Koehler PJ, Uitdehaag BM. The diagnostic value of provocative clinical tests in ulnar neuropathy at the elbow is marginal. J Neurol Neurosurg Psychiatry. 2009 Dec;80(12):1369-74.

8. Cutts S. Cubital tunnel syndrome. Postgrad Med J. 2007 Jan;83(975):28-31.

9. Ayromlou H, Tarzamni MK, Daghighi MH, Pezeshki MZ, Yazdchi M, Sadeghi-Hokmabadi E, Sharifipour E, Ghabili K. Diagnostic value of ultrasonography and magnetic resonance imaging in ulnar neuropathy at the elbow. ISRN Neurol. 2012;2012:491892.

10. Padua L, Aprile I, Caliandro P, Foschini M, Mazza S, Tonali P. Natural history of ulnar entrapment at elbow. Clin Neurophysiol. 2002 Dec;113(12):1980-4.

11. Zlowodzki M, Chan S, Bhandari M, Kalliainen L, Schubert W. Anterior transposition compared with simple decompression for treatment of cubital tunnel syndrome. A meta-analysis of randomized, controlled trials. J Bone Joint Surg Am. 2007 Dec;89(12):2591-8. 

12. Beekman R, Wokke JH, Schoemaker MC, Lee ML, Visser LH. Ulnar neuropathy at the elbow: follow-up and prognostic factors determining outcome. Neurology. 2004 Nov 09;63(9):1675-80. 

13. Lowe JB, Maggi SP, Mackinnon SE. The position of crossing branches of the medial antebrachial cutaneous nerve during cubital tunnel surgery in humans. Plast Reconstr Surg. 2004 Sep 01;114(3):692-6.