Cubital Tunnel Syndrome (CTS) involves the irritation or compression of a major nerve as it passes through a narrow channel on the inner side of the elbow. This compression leads to discomfort, numbness, and often tingling in the hand and arm. CTS is an entrapment neuropathy, meaning a peripheral nerve is physically trapped or squeezed by surrounding structures. The causes of this entrapment range from the inherent anatomy of the elbow joint to daily habits and underlying medical conditions.
The Ulnar Nerve Pathway and Compression Site
The ulnar nerve runs from the neck down to the hand. At the elbow, this nerve passes through a constricted passageway known as the cubital tunnel, which is bordered by bone and covered by a fibrous roof called Osborne’s ligament. This tunnel is located directly behind the medial epicondyle, the bony prominence commonly referred to as the “funny bone.”
The nerve is particularly vulnerable at this site because it is not significantly cushioned by muscle or fat, leaving it exposed to external pressure and internal strain. Within the cubital tunnel, the nerve becomes injured through direct compression and excessive stretching. When the elbow is bent deeply, the volume of the cubital tunnel naturally decreases, which physically squeezes the nerve. Simultaneously, bending the elbow causes the ulnar nerve to stretch around the bony bump of the medial epicondyle, placing tension on the nerve fibers.
Habits and Activities That Trigger Nerve Pressure
Prolonged and repetitive elbow flexion is a major contributor to nerve irritation, as this posture significantly narrows the space within the cubital tunnel. Activities like holding a telephone to the ear, driving with the elbow sharply bent, or sleeping with the arms tightly folded against the chest can maintain this harmful position for extended periods.
Direct, sustained pressure on the elbow’s inner side is another frequent cause of nerve irritation. Resting the elbow on a hard surface, such as a desk edge, a car armrest, or the arm of a chair, transmits external force directly onto the vulnerable nerve. This sustained pressure can exacerbate the nerve’s internal compression or stretching.
Repetitive motions, often associated with occupational or athletic activities, can also lead to chronic strain. Jobs requiring frequent, forceful elbow movements, such as assembly line work or the use of vibrating hand tools, increase the risk of developing symptoms. In sports, activities that involve high-velocity, repetitive elbow movements, like the pitching motion in baseball, place extreme traction and stress on the tissues surrounding the cubital tunnel, leading to inflammation and nerve irritation.
Physical and Structural Factors
One significant factor in developing Cubital Tunnel Syndrome is previous trauma to the elbow, such as a fracture or dislocation, which can alter the normal bony anatomy of the joint. These injuries may lead to the formation of scar tissue or bone spurs. These growths physically narrow the cubital tunnel and continually impinge upon the ulnar nerve.
Underlying medical conditions, including osteoarthritis and rheumatoid arthritis, can cause inflammation and swelling within the joint capsule. This fluid buildup, or edema, increases the internal pressure around the nerve, compressing it against the tunnel walls. Furthermore, the arthritis process can lead to the growth of osteophytes, or bone growths, that physically restrict the nerve’s movement.
In some people, the ulnar nerve exhibits a structural anomaly where it is hypermobile, meaning it does not stay securely within the cubital tunnel. When the elbow is flexed, this nerve may visibly snap or shift over the medial epicondyle, a phenomenon known as ulnar nerve subluxation. Less commonly, some individuals are born with an extra muscle or fibrous band across the nerve, which can mechanically squeeze the ulnar nerve and cause symptoms.