Ulnar nerve entrapment is a disease caused by increased pressure on the ulnar nerve, usually at the elbow, causing a decrease in blood supply to the nerve, and the consequent progressive degeneration of the nerve due to lack of oxygen and nutrients.
The ulnar nerve circulates along the posterior and medial aspect of the elbow, and is commonly known in our environment as the “funny bone”. In reality, it is not a bone, but a peripheral nerve that provides sensitivity and movement to our hand; however, it is true that at the level of the elbow it is located between two bony prominences called the olecranon and medial epicondyle. At this level, it passes through a tunnel formed by these bones as walls and the medial collateral ligament of the elbow as the floor of the tunnel, which is also hard and inelastic. Closing the tunnel as a roof, there is an arch formed by a resistant fascia that joins the two fascicles of a muscle called flexor carpi ulnaris. It is in this tunnel, where the ulnar nerve can end up compressed, especially with the flexion of the elbow in a maintained way (when holding a book to read for example, or putting the forearm under the pillow or holding the sheets close to the body during the night), or be compressed in other places of the elbow or the forearm with the support on the table or in the armrest of a chair.
Ulnar nerve entrapment does not usually cause pain, only the gradual loss of nerve function as described below. In the case of a prolonged period of time, this loss of function may not be completely recovered in spite of a correct treatment.
There is another group of patients with ulnar nerve irritation, known as ulnar neuritis, in which the problem is not increased pressure and lack of blood supply to the nerve, but increased mobility of the nerve, which can be mechanically irritated by friction against neighboring surfaces as it enters and leaves its normal path during elbow movements.
This mechanical irritation generally produces pain of the nerve itself on the inner aspect of the elbow and in its course to the fourth and fifth fingers of the hand. If the irritation mechanism is prolonged in time, it can end up producing a lack of nerve function, resulting in a true neuropathy due to nerve degeneration caused by repetitive irritation and inflammation over weeks or months.
Functions of the ulnar nerve
The ulnar nerve has two well-defined functions:
1. Provide sensitivity in the skin of the fifth finger (little finger), the middle of the fourth finger in contact with the fifth finger, and the skin of the back and palm of the hand that continue with this fifth and fourth finger up to the wrist.
2. Giving movement to the muscles located in the hand, responsible for the fine and precision movements of the fingers, as well as part of the muscles of the forearm that allow us to flex the fourth and fifth fingers and flex our wrist towards the inner side of the forearm.
When the ulnar nerve degenerates, it progressively loses its function. Therefore, there are alterations in the sensitivity of the skin, with sensations of corking or needle-like, and lack of sensitivity when touching objects with the fifth finger, the half of the fourth finger closest to the previous one, and the edge of the hand that continues with the fourth and fifth fingers up to the wrist.
Likewise, if its motor function is affected, hand dexterity is lost, since the muscles that perform fine finger movements stop working properly. The result is that the person with a motor impairment of the ulnar nerve is clumsy, drops objects, and takes longer to perform tasks such as buttoning a shirt or threading a needle; you will notice that you are losing the strength and precision to perform the clamp between the first finger and the rest of the fingers, having difficulty turning the key of a lock, or open a jar.
If the lesion continues to progress, the skin of the aforementioned territory may not be felt, as if it were anesthetized. The hand loses its muscles, appearing bony and progressively flexing the fourth and fifth fingers, in what has come to be called the ulnar claw, or preacher’s hand. The severe involvement of this musculature prevents the use of the hand for most of the activities we perform, with very important consequences for the autonomy and quality of life of people.
How long does it take for the ulnar nerve to recover?
Once the ulnar nerve is injured, its evolution is unpredictable. There are people who gradually improve until the disease disappears, others remain stable over time without changing their symptoms for months, and a third group of patients gets progressively worse, with all the lesions and characteristics of the disease described above appearing gradually.
Sometimes, the progression of symptoms is explosive, with very severe lesions appearing in a few days or weeks of evolution. The differences in the evolution will be determined by the intensity of the lack of irrigation to the nerve, which unfortunately is not easy to measure with diagnostic tests. The key in this disease is to provide the nerve with the means to recover as soon as possible, that is, to eliminate the mechanisms that limit the blood supply so that the nerve structure is not damaged, and if it has been damaged, it can try to regenerate itself. The structure of a nerve can be understood in a simple way as a light wire, with a thick plastic sheath on the outside, and many copper wires on the inside that conduct electricity (the nerve impulse) but each one of them is surrounded by a thin plastic sheath.
The copper fibers would be the axons, extensions of the neurons that reside in the spinal cord in our neck and reach the muscles and skin of the hand. The sheaths would be formed by myelin, which forms a tunnel through which each of the nerve axons circulates. If the injury has been present for a short time and is not severe, treatment can be very effective and nerve function can be fully restored within a few weeks.
However, if the injury is more severe and takes longer, a variable number of axons may have been lost, and after treatment these axons may have to regrow from the site of injury into the intact myelin tunnels; this growth occurs at a rate of approximately 1-2 mm per day, which may take more than a year to reach from the elbow to the fingertip. Finally, if the lesion is very severe, the myelin conduits through which the axons have to grow may have closed or have been occupied by scar tissue, so that the axons cannot find their way, and nerve function does not recover despite proper treatment.
The diagnosis is established by the presence of symptoms and signs that appear during physical examination of the elbow and ulnar nerve pathway. Electrophysiology (electromyography and electroneurography), although an uncomfortable test, is important to establish the location of the lesion and its severity. These tests are only effective when performed at least 3 weeks after the onset of the lesion. The intensity of the lesion on electrophysiology, the time of evolution since the onset of symptoms and age are all factors related to the capacity of response and recovery after the correct treatment of this disease.
Treatment of the ulnar nerve
The first measure to take immediately is to avoid the mechanisms that produce the injury, especially keeping the elbows bent at night, and the support on the forearms or elbow while sitting or working. For some people it can be very complicated to control the position of the elbows while sleeping, and in this case it is possible to use elbow immobilization orthoses locked in extension, or home methods such as surrounding the limb with a thick folded towel to prevent the elbow from flexing during the night. Moving the chair away from the desk to keep the forearms in the air while resting the wrists or hands on the desk and keeping the elbows slightly bent, are strategies that help avoid pressure from resting on the nerve.
Your elbow orthopedist will evaluate the skin sensitivity of the ulnar nerve territory and the strength of the muscles innervated by the ulnar nerve. He will also look for signs of atrophy of the hand musculature. Finally, he/she will look for the site of the entrapment with the physical examination. If the symptoms have been present for more than 3 weeks, he will ask you to perform an electrophysiological test to establish the location of the lesion (usually at the elbow), its intensity (mild, moderate or severe), and its nature (entrapment versus medical diseases of the nerves). Based on all the information gathered, a treatment plan will be proposed.
If the symptoms and intensity of the electrophysiology lesion are mild, especially if the patient perceives that it is improving over time, conservative treatment aimed at avoiding the cause of the nerve injury will be instituted. However, if the injury is moderate or severe, and especially if there is muscle weakness (motor involvement), your doctor will propose a definitive treatment consisting of decompressing the ulnar nerve to allow blood to reach the nerve normally and avoid mechanical compression of the nerve, stopping the disease and giving the nerve a chance to recover.
Surgical treatment of ulnar neuropathy is aimed at eliminating the compression points on the nerve, stopping the disease, and allowing the nerve to regenerate and recover its function. As mentioned above, this regenerative capacity is determined by the duration of the disease, the age of the patient, and the intensity of the damage in electrophysiological tests. Therefore, the sooner action is taken, whenever indicated, the greater the chances of success in this recovery of lost sensitivity and strength.
There are three types of ulnar nerve surgery, which are used depending on the type of symptoms, the intensity of the injury, and the anatomical characteristics of the affected person’s elbow.
1. In situ decompression. This is the least aggressive intervention. It is performed with a small incision of about 4 cm on the inner side of the elbow, and the nerve is decompressed without touching it, releasing the surrounding layers and the pressure they exert on the nerve.
2. Subcutaneous transposition. In addition to the release, the nerve is moved to a more anterior location, protecting it from the traction produced by elbow flexion in activities of daily living. It is used in more intense injuries and in those nerves with increased mobility and ability to move out of its path with elbow movements (see above).
3. Submuscular transposition. The nerve is placed together with the rest of the nerves and blood vessels that go to the hand, in a deeper location under the forearm musculature. It is used in the most severe cases or those resistant to other treatments, and in the case of very painful irritative neuritis.
All three types of surgery are usually performed on an outpatient basis without the need for hospitalization. It is usually performed under regional anesthesia, only by numbing the arm, elbow and forearm using local anesthesia on the nerves of the upper limb.
The surgery allows the use of the hand, elbow and shoulder from 24 hours after the intervention, allowing the use of the hand on the operated side for self-care (toileting, dressing and feeding) and allowing free movement of the limb joints immediately, while protecting the wound region until healing.