What is an Anterior Interosseous Nerve Syndrome (AINS)
Anterior interosseous nerve syndrome is a nerve disorder that causes pain and weakness in the hand and forearm. The anterior interosseous nerve starts near the inside of the elbow and continues down the forearm, between the two main bones of the forearm. This nerve provides feeling to the muscles of the index and middle fingers, the thumb, and the forearm. This condition is caused by unusual pressure (compression) on the anterior interosseous nerve.
AINS affects hand and forearm function, and it may cause muscle weakness and pain.
What are the causes?
This condition is caused by compression of the anterior interosseous nerve. Compression may result from:
- Nerve injury (trauma).
- Abnormal position of a cord of tissue that connects a muscle to a bone (tendon).
- Abnormal position of a blood vessel.
- Overgrowth of a forearm muscle (hypertrophy).
- Formation of a blood clot (thrombosis) in the main forearm artery (radial artery).
- Formation of tissue between muscles of the forearm.
In some cases, AINS may occur when the nerve is not compressed (spontaneous anterior interosseous nerve syndrome). The cause of spontaneous AINS is not known.
What increases the risk?
The following factors may make you more likely to develop this condition:
- Doing repetitive and intense movements of the forearm and wrist, especially wrist and hand rotation.
- Having poor strength and flexibility.
- Having type 1 diabetes mellitus.
- Having an underactive thyroid gland (hypothyroidism).
What are the signs or symptoms?
Symptoms of AINS may include:
- Pain in the upper forearm, near the elbow.
- Difficulty touching the index finger to the thumb.
- Weakness in the thumb and index finger, especially when bending the thumb or turning the palm down against resistance.
- Difficulty writing.
- Frequently dropping objects.
How is this diagnosed?
This condition may be diagnosed based on your symptoms, your medical history, and a physical exam. You may have tests, such as:
- Electromyogram (EMG). This measures the electrical activity in your arm and hand muscles.
- Ultrasound.
- MRI.
- Magnetic resonance neurogram (MRN). This creates images of your nerve.
How is this treated?
Treatment depends on the cause of your condition. Treatment usually includes:
- Stopping activities that cause pain.
- A hand or arm splint.
- Medicines that help to relieve pain and inflammation.
- Shots (injections) of medicines that help to reduce inflammation (steroids).
- Icing or applying heat to the injured area, as told by your health care provider.
- Physical therapy to strengthen and stretch your forearm, elbow, and hand.
In some cases, you may have surgery to relieve pressure on the nerve. This may be done if:
- A treatable cause is found.
- Your condition is severe.
- Your symptoms do not improve after 8 weeks of other treatment methods.
Follow these instructions at home:
If you have a splint:
- Do notput pressure on any part of the splint until it is fully hardened. This may take several hours.
- Wear the splint as told by your health care provider. Remove it only as told by your health care provider.
- Loosen the splint if your fingers tingle, become numb, or turn cold and blue.
- Do
notlet your splint get wet if it is not waterproof.
- Do nottake baths, swim, or use a hot tub until your health care provider approves. Ask your health care provider if you can take showers. You may only be allowed to take sponge baths for bathing.
- If your splint is not waterproof, cover it with a watertight covering when you take a bath or a shower.
- Keep the splint clean.
Managing pain, stiffness, and swelling
- Move your fingers often to avoid stiffness and to lessen swelling.
- Raise (elevate) your injured arm above the level of your heart while you are sitting or lying down.
- If
directed, apply ice to the injured area:
- Put ice in a plastic bag.
- Place a towel between your skin and the bag.
- Leave the ice on for 20 minutes, 2–3 times a day.
- If
directed, apply heat to the affected area as often as told by your health
care provider. Use the heat source that your health care provider
recommends, such as a moist heat pack or a heating pad.
- Place a towel between your skin and the heat source.
- Leave the heat on for 20–30 minutes.
- Remove the heat if your skin turns bright red. This is especially important if you are unable to feel pain, heat, or cold. You may have a greater risk of getting burned.
Driving
- Do notdrive or operate heavy machinery while taking prescription pain medicine.
- Ask your health care provider when it is safe to drive if you have a splint on your hand or arm.
Activity
- Return to your normal activities as told by your health care provider. Ask your health care provider what activities are safe for you.
- Do physical therapy exercises as told by your health care provider.
General instructions
- Take over-the-counter and prescription medicines only as told by your health care provider.
- Keep all follow-up visits as told by your health care provider. This is important.
Contact a health care provider if:
- You have symptoms that get worse or do not get better after 8 weeks of treatment.
- Your hands feel numb or cold.
- Your fingernails turn a dark color, such as blue or gray.
