Cubital tunnel syndrome (CuTS) is an entrapment neuropathy, or nerve compression syndrome, a condition caused by compression, traction, or friction of the ulnar nerve at the elbow. Nerve compression is also known as a trapped nerve. The ulnar nerve travels from the brachial plexus down the length of the arm to the hand. Along its course, it may become compressed at several sites. At the elbow, the ulnar nerve passes through the cubital tunnel, where ulnar nerve compression most commonly occurs. The ulnar nerve provides motor and sensory innervation to the forearm and hand, and its compression can cause numbness and other symptoms associated with cubital tunnel syndrome, commonly in the fourth and fifth fingers. Symptoms may include a claw hand. Cubital tunnel syndrome is an ulnar neuropathy that can be caused not only by compression at the cubital tunnel level itself, but can also be caused by movement of the elbow. The volume of the cubital tunnel may be reduced when being moved from full extension to a lesser degree of flexion. In many cases, the cause of CuTS is unknown. Diagnosis can be made with clinical symptoms, physical examination, imaging, and electrodiagnostic tests. There is currently no standardized method for diagnosing CuTS. Common physical exam findings would involve testing for paresthesia symptoms with a Tinel's test or checking for sensation in the 4th and 5th digits. Conservative management of CuTS includes positional/ergonomic changes to reduce elbow flexion, elbow bracing, NSAIDs, and physical or occupational therapy. Surgery to decompress or relocate the ulnar nerve is the only disease-modifying treatment.
Anatomy
The ulnar nerve arises from the medial cord of the brachial plexus , containing mostly C8 and T1 nerve fibers. While originally starting in the anterior compartment of the arm, the nerve enters the posterior compartment prior to arriving in the cubital tunnel. The cubital tunnel is an anatomical space that lies within the dorsomedial aspect of the elbow. The ulnar nerve lies within this groove and is bordered medially by the humeral medial epicondyle and laterally by the ulna's olecranon process. The band of tissue that overlies the cubital tunnel is often called Osborne's ligament and connects the heads of the flexor carpi ulnaris muscle. Alternative names for Osborne's ligament include Osborne's fascia, Osborne's band, or the cubital tunnel retinaculum. There are several anatomic variations of Osborne's ligament that range from its absence to increased thickness, or the fascia being replaced altogether by the aconeus epitrochlearis, an accessory muscle. An additional fibrous band known as Struthers' ligament or arcade exists more proximally to the cubital tunnel connecting the supracondylar humeral process and the medial humeral epicondyle.
Pathophysiology
Causes of nerve injury can vary from direct pressure, nerve sliding, trauma, or overuse of a joint. Cubital tunnel syndrome most often describes a compression of the ulnar nerve underneath Osborne's ligament, but the Struthers' ligament could be another etiology that is more proximal in origin. There are several sites of possible compression, traction, or friction of the ulnar nerve as it courses behind the elbow. As the elbow flexes, this leads to a decreased cross-sectional area of the cubital tunnel and potential compression of the ulnar nerve. This is thought to worsen neuropathy symptoms overnight as elbows and wrists tend to flex during sleep. There are a number of modifiable risk factors that are associated with cubital tunnel syndrome, including smoking, diabetes, hypertension, and an elevated body mass index. Additional comorbid conditions were associated with concomitant carpal tunnel syndrome, osteoarthritis, rheumatoid arthritis, and gastroesophageal reflux disease.
Epidemiology Cubital tunnel syndrome is the second most prevalent compression neuropathy of the upper extremity, following carpal tunnel syndrome. While the symptomatic prevalence is roughly estimated to be around 5.9%, there is a notable lack of epidemiological studies. Furthermore, the prevalence could potentially be underestimated due to a lack of specific diagnostic criteria or self-treatment with conservative measures such as over-the-counter medications and rest.
Signs and symptoms
Early characteristic symptoms tend to involve sensation, including numbness and tingling in the 4th and 5th fingers and the ulnar aspect of the hand. These areas process sensation through the ulnar nerve. Numbness or tingling sensations tend to worsen at night or with activities that involve flexing the elbow joint. As the neuropathy advances, loss of sensation could replace the paresthesia symptoms. Motor function tends to be impacted later, with fine motor skills of the hand being affected. Motor function of the ulnar nerve is responsible for thumb adduction and flexion of the wrist, 4th, and 5th fingers. Weakness in these muscle groups can be observed. As the compression progresses to a chronic stage, atrophy in the hypothenar muscle belly can be appreciated.
Diagnosis There is not a consensus standard to diagnose cubital tunnel syndrome, but a combination of physical exam, imaging, and electrodiagnostic testing are utilized. Still, 93% of surgeons order preoperative tests (most order electrodiagnostics only, whilst others order a mixture of electrodiagnostics and imaging). Moreover, 6 in 10 surgeons still operate when test results are normal. Overall, there is considerable uncertainty over the utility, cost-effectiveness and thresholds of medical tests for diagnosing CuTS.
Physical exam
Clinical examination should include inspection of the hand to see hypothenar muscle atrophy and checking sensation and strength. The diagnosis of CuTS can be further supported with some observable signs or maneuvers. These signs include the following:
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