Cubital tunnel syndrome

Epidemiology and terminology issue

Ulnar neuropathy at the elbow occurs in 6% of the population. The average incidence is 24.7 cases per 100,000 population. Men are affected more frequently: the incidence rate reaches 25.2–32.7 per 100,000 in men, whereas in women it ranges between 17.2–18.9 per 100,000. Non-traumatic nerve lesions in other areas are extremely rare, and reliable statistics for Guyon's canal syndrome are currently lacking.

In clinical practice, it is preferable to use the term «ulnar neuropathy at the elbow». The conventional name «cubital tunnel syndrome» is anatomically not entirely correct. The fact is that in 75% of cases, compression occurs in the retroepicondylar groove, and only in 25% directly in the cubital tunnel. However, there is no consensus among specialists, and some authors include the groove as part of the canal.

Anatomy of compression and clinical presentation

Compression of the nerve trunk in the elbow region can occur in two main zones, although the clinical picture remains identical:

1. In the cubital tunnel itself. It is formed by the ulnar nerve groove (located posterior to the medial epicondyle of the humerus) and a fibrous band stretched between the medial epicondyle and the olecranon.
2. At the exit from the canal. Here the nerve is compressed by a fibrous arch stretched between the two heads of the flexor carpi ulnaris muscle (m. flexor carpi ulnaris).

Clinical manifestations develop gradually:

• Sensory disturbances: palpation and percussion of the nerve trunk at the elbow cause pain and paresthesias in the area of its innervation on the hand.
• Motor disturbances: as the disease progresses, weakness in adduction and abduction of the 4th and 5th fingers appears.
• Specific signs: in late stages, muscle atrophy develops and a typical deformity is formed — «claw hand».

Basic diagnostics of entrapment syndromes

General clinical diagnostic methods are used to identify the level of compression:

• Palpation: allows determining local tenderness of the nerve trunk precisely at the site of compression.
• Tinel's sign: a valuable diagnostic sign where percussion of the nerve causes painful paresthesias in its innervation zone.
• Diagnostic block: perineural injection of a mixture of novocaine and hydrocortisone into the suspected compression zone. If the procedure does not provide even partial temporary relief, compression at this level is excluded with high probability.

To understand the general picture, it is useful to know the approximate frequency of compression of various peripheral nerves:

• Median nerve (carpal tunnel) — 45%
• Ulnar nerve (cubital tunnel) — 15%
• Fibular nerve (at the fibular head) — 10%
• Radial nerve (in the arm) — 4%
• Tibial nerve (tarsal tunnel) — 3%
• Other entrapment syndromes account for 1–2% each.

Instrumental diagnostic methods

Three main methods are used to confirm the diagnosis and for differential diagnosis:

• Needle electromyography (EMG). Level of recommendation: C. Indicated when a lesion in Guyon's canal is suspected. The target muscle is m. flexor carpi ulnaris. If changes are detected in it, this indicates a high level of lesion (proximal to Guyon's canal) and rules out Guyon's canal syndrome.
• Ultrasound examination (US). Level of recommendation: C/B. The cross-sectional area of the nerve is evaluated at the level of the cubital tunnel and Guyon's canal. Ultrasound allows visualizing the nerve structure in compression zones. A reliable criterion for cubital syndrome is considered to be an increase in the cross-sectional area greater than 10 mm².
• Magnetic resonance imaging (MRI). Level of recommendation: A. Prescribed when ultrasound is insufficiently informative. MRI of the elbow joint and soft tissues with contrast is performed. Specific signs: nerve thickening and increased signal intensity in T2 or STIR modes.

Class and exam questions

What else to study on this topic

• Carpal tunnel syndrome
• Pronator teres syndrome of the median nerve
• Ulnar neuropathy at the level of Guyon's canal
• Methodology for performing needle EMG of peripheral nerves
• Ultrasound anatomy of the peripheral nerves of the upper extremity

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