The ulnar nerve provides sensory and motor innervation to the little and ring finger, radial half of the hand, flexor carpi ulnaris, and flexor digitorum profundus. Abnormally high pressure on the nerve leads to inflammation and sensory and motor deficits along the region of the nerve distribution.
Based on the position of inflammation, ulnar nerve entrapment is of two forms.
- Cubital tunnel syndrome is the nerve entrapment at the elbow where the nerve passes through the cubital tunnel.
- Guyon’s tunnel syndrome results from the compression at the wrist level as the nerve passes through the ulnar or Guyon’s tunnel.
They cause pain in the hand and forearm, restricting the freedom of motion. Hence, they affect daily activities that require finger and hand movement.
Prolonged inflammation may result in severe neuropathy. Therefore, patients need medical attention to rectify the root cause at its initial stages.
Causes of Ulnar Nerve Entrapment
All ulnar nerve entrapment causes nerve inflammation and neurological deficits in its innervated muscles. The causes are as follows.
- Nerve Compression at Various Points Along its Path
Compression of the nerve at the elbow as it passes through the cubital tunnel is the most common due to Osborne’s ligament adjacent to it. The nerve bifurcates into the deep motor and superficial sensory branch as it passes through the ulnar canal.
The Ulnar canal has three zones. Zone 1 is proximal to the nerve before bifurcation. Zone 2 surrounds the deep motor branch, and zone 3 envelopes the sensory path of the ulnar nerve.
- Entrapment at zone 1 impairs both the nerve’s motor outputs and sensory inputs.
- Compression in zone 2 leads to motor dysfunctions.
- Pathology at zone 3 causes sensory deficits.
- Repetitive Motions or Overuse Injuries
Repetitive but low impact to the wrist during activities like driving a bike or typing on a keyboard may cause ulnar nerve entrapment at the wrist. Excessive flexion of the elbow may lead to compression between the medial collateral and Osbourne’s ligaments resulting in ulnar nerve compression at the elbow.
- Direct Trauma to the Nerve
Impact on the region over the cubital or ulnar tunnel causes ulnar nerve contusion. It is also called hitting your funny bone.
- Certain Medical Conditions or Anatomical Abnormalities
Radiculopathy from C8 spinal nerve root can impede nerve impulse conduction downstream through the ulnar nerve.
Symptoms of Ulnar Nerve Entrapment
Ulnar nerve entrapment symptoms are briefly discussed below.
- Numbness or Tingling
They experience numbness due to loss of motor control over the intrinsic muscles of the hand and little and ring finger. Patients may not sense the radial half of their affected hand due to sensory nerve damage.
- Weakness in the Hand or Wrist
As the muscles of the hand lose motor control, the electrical stimulation diminishes, and the muscles lose their masses and become weak.
- Pain or Discomfort in the Elbow or Forearm
Patients may feel pain inside the elbow or wrists due to compression of the region around the nerve.
- Difficulty with Fine Motor Movements
As the fingers lose partial control over their movement, they can coordinate with each other and perform the intended task, such as buttoning a shirt.
Diagnosis of Ulnar Nerve Entrapment
- Physical Examination by a Doctor
The examiner tests the ability to sense light touch and differentiate between two points on the dorsal and volar surfaces of the radial half of the hand.
- Froment’s Test
The examiner asks the patient to hold a piece of paper between the thumb and the radial side of the index finger. If the thumb of the patient flexes at the interphalangeal joint, contacting it by the tip of the thumb, the test is positive.
- Wartenberg’s Test
When the patient held the affected hand and fingers adducted with interphalangeal joints extended, the little finger swung away from the ring finger. It indicates ulnar nerve damage.
- Nerve Conduction Studies
These studies show delayed impulse detection and low amplitude from muscles innervated by the ulnar nerve. They include
- Thenar and hypothenar muscles, little and ring fingertips upon damage at the wrist
- Flexor digitorum profundus, flexor carpi ulnaris, and abovementioned muscles when entrapment has occurred at the elbow.
- Electromyography (EMG)
EMG of the little finger, ring finger, and intrinsic muscle of the hand and forearm demonstrate increased distal latency and decreased conduction velocity showing neuropathy with muscle denervation.
- Imaging Tests
X-rays of the elbow and wrists help rule out the osseous deformity that causes nerve entrapment. A cervical spine X-ray rules out the pinching of the corresponding nerve root of the spinal cord. Chest X-ray is to check for the compression of the medial cord by an apical lung or Pancoast tumour.
MRI reveals cervical radiculopathy at the neck and other space-occupying lesions in the wrist. Ultrasound help measure the size of the ulnar nerve and compare it with that of the control. It also helps identify thrombosis of the ulnar artery, which presents with symptoms of ulnar nerve compression at the level of the ulnar canal.
Treatment Options for Ulnar Nerve Entrapment
- Conservative Treatments
- Doctors may suggest exercises that increase the ease of the ulnar nerve gliding through the cubital tunnel.
- Rest to the arm, including the elbow, reduces the pressure on the nerve from surrounding muscles and ligaments.
- Manual therapy from a certified therapist may relieve the ulnar nerve entrapment symptoms.
- Medications for Pain Relief or Inflammation
Over-the-counter non-steroidal anti-inflammatory drugs, such as ibuprofen, naproxen, and aspirin, can reduce pain and inflammation.
- Splinting or Bracing
Splints and braces hold wrists and elbows in a position restricting their movement. It reduces the activities of surrounding structures that increase the pressure on the ulnar nerve.
- Steroid Injections
Administration of corticosteroids under ultrasound into the region around the nerve entrapment reduces inflammation and pain. Cortisone is the most potent candidate.
- Surgery
Surgical interventions for cubital tunnel syndrome are discussed below.
- Ulnar Nerve Transposition
This procedure refers to positioning the ulnar nerve superficially to the flexor-pronator origin and anterior to the axis of elbow motion.
- Surgical Release of Osborne’s Ligament
This procedure involves the excision of the ligament posteriorly and medially to make space for the ulnar nerve to move freely.
- Medial Epicondylectomy
It is the excision of the medial epicondyle releasing the pressure on the ulnar nerve. It offers minimal risk of nerve injury but a high risk of elbow instability.
Conclusion
Driving bikes for long periods and tapping wrists repetitively while typing on a keyboard are the common causes of ulnar nerve entrapment. Devising the ergonomic aspects of our activities helps reduce the risk of the condition. While mild inflammations may respond to non-surgical treatment options, severe cases need surgical intervention.
It may prove detrimental if left untreated as it is an inflammatory condition that worsens as the compression persists. Hence, pain management alone does not help prevent complications. Therefore, patients should receive medical attention from an orthopaedic surgeon to avoid the risks.