Cubital tunnel syndrome refers to symptoms and signs caused by chronic injury to the ulnar nerve at the cubital tunnel in the elbow region.
Anatomical Overview
The cubital tunnel is a bony groove between the medial epicondyle of the humerus and the olecranon. It is covered by the ulnar collateral ligament, the fascia of the flexor carpi ulnaris, and the arcuate ligament. The channel formed between them is referred to as the cubital tunnel. The ulnar nerve is confined within this tunnel and is repeatedly stretched or relaxed during elbow flexion and extension.
Etiology
Various structural and morphological abnormalities of the cubital tunnel can result in compression of the ulnar nerve. Common causes include the following:
Cubitus Valgus Deformity
This is the most common cause. It can result from childhood supracondylar fractures of the humerus or damage to the lateral humeral epicondyle growth plate, leading to valgus deformity of the elbow. In such cases, the ulnar nerve is displaced medially in an arcuate shape, increasing its tension, especially during elbow flexion. Repeated friction within the cubital tunnel can lead to chronic traumatic inflammation or degeneration of the ulnar nerve. Mild valgus deformity may only cause symptoms decades later, hence the term "delayed ulnar neuritis," while severe deformity may result in symptoms within a year or two.
Ulnar Nerve Subluxation
A shallow congenital ulnar groove or laxity of the fascia and ligamentous structures overlying the cubital tunnel can cause the ulnar nerve to slip out of the ulnar groove during elbow flexion. Repeated slippage can lead to nerve friction, impact, and damage.
Medial Epicondyle Fracture of the Humerus
Displacement of the fracture fragment inferiorly can compress the ulnar nerve.
Post-Traumatic Ossification
The elbow joint is particularly prone to developing myositis ossificans following trauma. When this occurs near the ulnar groove, it can lead to compression of the ulnar nerve.
Clinical Features
Initial symptoms involve sensory disturbances on the ulnar side of the dorsum of the hand, the hypothenar region, the little finger, and the ulnar half of the ring finger, often described as numbness or tingling.
Following an extended period of sensory disturbance, patients may experience weakness in grip strength, particularly involving the little finger, as well as difficulty in finger adduction and abduction.
Physical examination may reveal atrophy of the hypothenar muscle and interosseous muscles, along with a claw-like deformity of the ring and little fingers. Sensation to pain is diminished in the affected areas. Additional findings may include a positive Froment sign, a positive paper grip test, and a positive Tinel's sign over the ulnar groove.
Electrophysiological studies typically demonstrate a slowing of nerve conduction velocity in the ulnar nerve distal to the elbow, along with abnormal electromyography findings in the hypothenar and interosseous muscles.
Underlying abnormalities may include structural deformities such as cubitus valgus or thickening of the ulnar groove region. X-rays may show displaced bone fragments, abnormal ossification, or other pathological findings in the region.
Differential Diagnosis
Cervical Radiculopathy (Radicular Type)
Narrowing of the intervertebral foramen can cause nerve root compression at C8, leading to sensory disturbances such as numbness and weakness along the ulnar side of the hand. These symptoms are similar to those of cubital tunnel syndrome but lack any abnormalities at the cubital tunnel itself. Electromyographic studies are helpful in differentiating the two conditions.
Neurilemmoma
Neurilemmoma of the ulnar nerve at the elbow may produce symptoms similar to those of cubital tunnel syndrome. Examination often reveals a segmental thickening of the ulnar nerve with a positive Tinel's sign, while there are no bony or joint abnormalities in the elbow region. In difficult cases, definitive diagnosis may require surgical exploration or pathological examination.
Treatment
Surgical exploration of the ulnar nerve is indicated if symptoms persist. If the nerve is found to be hardened or narrowed, epineurotomy or interfascicular neurolysis may be performed. The ulnar nerve can also be transposed from the ulnar groove to the anterior region of the elbow. Postoperatively, sensory recovery tends to occur relatively quickly, but atrophied intrinsic hand muscles may be challenging to restore to their normal size.