Cubital Tunnel Syndrome (CTS) is a disorder caused by the compression or stretching of the ulnar nerve as it passes through a narrow tunnel on the inside of the elbow. Its primary functions include providing sensation to the ring and little fingers and controlling most of the small, intrinsic muscles within the hand. Diagnosing this condition requires a structured, step-by-step process. This process combines patient reporting, physical maneuvers, and specialized technical testing to confirm the nerve entrapment and measure its severity.
Initial Clinical Assessment
The diagnostic process begins with a patient interview to understand the nature and onset of the symptoms. A physician will inquire about the location and quality of the discomfort, which typically includes numbness or tingling in the little finger and the ulnar half of the ring finger. They will also ask about activities or positions that worsen the symptoms, such as prolonged elbow flexion or resting the elbow on a hard surface.
The physician then performs an objective checkup, looking for signs of nerve dysfunction. They test for sensory deficits in the dermatome supplied by the ulnar nerve (C8-T1 nerve roots). Observations are made for muscle wasting, particularly in the small hand muscles, which signals advanced injury. Weakness is assessed in ulnar-controlled muscles, manifesting as difficulty with fine motor tasks like pinching or gripping.
The clinical examination also seeks to distinguish Cubital Tunnel Syndrome from other conditions that can cause similar C8-T1 symptoms, such as nerve root compression in the neck. Sensation on the back of the hand, over the ulnar side, is specifically checked. If sensation is preserved here, it suggests the compression is at the elbow, not further down in the wrist’s Guyon’s canal, because the sensory branch supplying this area separates from the main nerve before the wrist.
Provocative Physical Examination Maneuvers
After the initial assessment, the physician uses specific physical maneuvers designed to temporarily irritate or stress the ulnar nerve at the elbow. These tests attempt to reproduce the patient’s familiar symptoms, providing objective evidence of nerve sensitivity or compression. These maneuvers are simple, non-invasive, and can often be performed within the examination room.
One common maneuver is Tinel’s sign, performed by lightly tapping the skin directly over the ulnar nerve as it passes through the cubital tunnel. A positive result occurs when this tapping causes an immediate, electric-shock-like sensation or tingling (paresthesia) that shoots down the forearm into the ring and little fingers. This response indicates that the nerve is hypersensitive or damaged at that location.
Another frequently used procedure is the Elbow Flexion Test, which places the ulnar nerve under tension and increases pressure within the cubital tunnel. The patient is asked to fully flex their elbow and maintain that position for a set duration, often between 30 seconds and three minutes. The test is considered positive if the patient experiences a rapid onset or worsening of their typical numbness and tingling symptoms in the ulnar nerve distribution. The combined Elbow Flexion and Compression Test, where pressure is applied over the nerve while the elbow is flexed, is a highly sensitive method for provoking symptoms.
Confirmatory Diagnostic Testing
While the patient history and physical exam can strongly suggest the diagnosis, electrodiagnostic testing is considered the definitive method for confirming Cubital Tunnel Syndrome and measuring its severity. This testing involves two main components: Nerve Conduction Studies (NCS) and Electromyography (EMG). These objective tools are used to differentiate mild cases from those involving significant nerve damage and to precisely localize the site of entrapment.
The Nerve Conduction Study (NCS) measures how quickly and how strongly electrical signals travel along the ulnar nerve. Small electrodes are placed on the skin, and a mild electrical impulse is delivered to the nerve at various points along the arm, including above and below the elbow. In a patient with CTS, the electrical signal traveling across the elbow segment of the nerve will be significantly slower than the signal traveling through the unaffected segments.
A significant slowing of the motor nerve conduction velocity (NCV) across the elbow segment is a strong indicator of nerve compression. The NCS also measures the amplitude of the nerve signal, which can be reduced in more severe cases. These measurements help confirm that the elbow, and not a higher location like the neck, is the source of the problem.
Electromyography (EMG) is typically performed immediately following the NCS and involves inserting a fine needle electrode directly into the muscles supplied by the ulnar nerve in the hand and forearm. The EMG assesses the electrical activity within the muscle fibers both at rest and during voluntary contraction. This test helps determine the long-term health of the muscle.
In cases of chronic or severe nerve compression, the EMG will show signs of denervation, indicating muscle fibers are losing their nerve supply. Abnormal electrical activity in the intrinsic hand muscles suggests that the nerve damage is significant enough to have caused muscle fiber damage. Conversely, a normal EMG with positive NCS findings may indicate a milder condition where the nerve is compressed but the muscle has not yet suffered permanent damage.
When Imaging is Necessary
Imaging studies are not typically the primary diagnostic tool for Cubital Tunnel Syndrome, but they serve an important function in the overall evaluation. These tests are primarily used to rule out secondary causes of nerve compression or to visualize the nerve itself when the diagnosis remains unclear after clinical and electrodiagnostic testing. Imaging helps to identify structural abnormalities that may be contributing to the ulnar nerve’s irritation.
A standard X-ray may be ordered to assess the bony structures around the elbow. While nerves are not visible on X-ray, this imaging can reveal bone spurs, signs of old fractures, or degenerative arthritis that could be physically narrowing the cubital tunnel and pressing on the ulnar nerve. Identifying these bony causes is important for surgical planning.
Ultrasound is increasingly utilized because it allows for direct visualization of the ulnar nerve and surrounding soft tissues. It can measure the nerve’s cross-sectional area; a swollen nerve is a sign of fluid build-up due to compression. Furthermore, a dynamic assessment can visualize the nerve as the elbow moves, identifying cases where the ulnar nerve “snaps” or subluxates out of its groove during flexion.
Magnetic Resonance Imaging (MRI) is generally reserved for complex cases or when a soft tissue mass is suspected to be the source of compression. The MRI provides highly detailed images of the soft tissues, allowing the physician to look for tumors, cysts, or other space-occupying lesions that might be pressing on the nerve. It can also show subtle signs of chronic nerve injury, such as edema or atrophy in the ulnar-innervated muscles of the forearm and hand.