Posterior interosseous nerve syndrome is not common. I have only seen a handful in my many years of practice in orthopedic physical therapy. Luckily, most of these patients came in soon after noticing symptoms and the condition was resolved quickly. Read on to learn more about posterior interosseous nerve syndrome. Let’s start with anatomy!
The elbow
The elbow joint is where the humerus, ulna, and radius come together. The humerus is the upper arm bone and forms individual joints with the ulna and radius, which are the forearm bones. Movements of the elbow include flexion and extension. Flexion is when the forearm and upper arm come closer together (bending the elbow) and extension is when move farther apart (straightening the elbow). The radioulnar joint allows for the movements of pronation and supination. Pronation is rotating the forearm, so the palm faces downward, and supination is forearm rotation where the palm faces upward.
The supinator
The supinator is a muscle just below the elbow. It attaches to the humerus and ulna. From there, it spirals around the radius and connects to several different areas of the radius. This positioning allows the supinator to perform the action of supination. It is a wide muscle with a superficial and deep layer. An arch is formed between the superficial and deep layers of the supinator muscles. This is called the arcade of Frohse.
The radial nerve
The radial nerve is one of the major nerves of the upper extremity. It begins near the armpit and travels all the way down to the hand. As it travels down the arm, the radial nerve will divide into superficial and deep branches at the level of the elbow. The superficial branch of the radial nerve only provides sensation and no motor function. It provides sensation to the back of the hand and wrist. The deep branch provides only motor innervation and no sensory.
The posterior interosseous nerve
The deep branch turns into posterior interosseous nerve as it goes into the supinator muscle. The posterior interosseous nerve enters at the arcade of Frohse. It travels between the superficial and deep layers of the supinator. The posterior interosseous nerve continues down the forearm to innervate the the muscles of wrist extension, finger extension, thumb extension, and thumb abduction. Wrist extension is when the back of the wrist moves toward the back of the forearm. Finger extension is straightening the fingers. Thumb extension is moving the thumb away from the index finger while thumb abduction is moving the thumb forward of the index finger.
What is posterior interosseous nerve (PIN) syndrome?
PIN syndrome is a compressive neuropathy of the posterior interosseous nerve. Neuropathy indicates some type of damage to the nerve. There are many different ways that the nerve could become compressed. These include:
- Micro trauma – Repetitive pronation and supination movements can lead to PIN syndrome. It is more common in manual laborers because of the repetitive forearm movements. The arcade of Frohse is the most common point of compression.
- Trauma – Traumatic injuries to the elbow and forearm can lead to PIN syndrome. Fractures (breaks) or dislocation at the area around the elbow could cause damage to the nerve.
- Space filling lesions – The compression on the nerve could also be caused by lipomas, ganglion cysts, or tumors.
- Inflammation – Inflammation in the area can cause compression to the nerve. Systemic conditions like rheumatoid arthritis can lead to this type of inflammation.
- Surgery – Injury to the nerve could also be a result of surgery in the area.
What are the symptoms of PIN syndrome
There are several symptoms associated with PIN syndrome. These include:
- Symptom occur gradually
- Pain in the forearm and wrist
- Weakness in wrist, finger, and thumb extension
- No changes in sensation
Who gets PIN syndrome?
PIN syndrome is rare and is more common in males than females. Manual laborers and body builders have increased risk of developing PIN syndrome.
Who should I see?
- Physical therapy – Physical therapy can help decrease pain and inflammation with techniques including manual therapy and dry needling. PT can evaluate and address abnormal joint mobility, muscle weakness, muscle tone, and flexibility. With PIN syndrome it is important to decrease the amount of work the supinator is performing. Your PT can help you activate other muscles to decrease the load on the supinator and other forearm muscles. They can assess your posture during work or sports to prevent the problem from happening again.
- Orthopedic physician – An orthopedist might be necessary if the condition is not responding to physical therapy. Your physician can prescribe medication, give a steroid injection, or order a nerve conduction test if needed. Surgery is an option if all conservative measures fail.
What can I do?
- Relative rest – Resting the area to decrease further pain and damage from occurring is one of the best ways to treat PIN syndrome. Basically, stay away from the activities that are causing pain. This gives the nerve time to heal. If you keep doing what is causing the injury, it is not going to get better. This might include not participating in your sport or changing how you perform a task or job. If you are not able to participate in your activity or sport, then you can supplement with non-irritating activities such as biking, walking, or jogging while your condition is being treated.
- Ice – Ice can help decrease pain and symptoms at the forearm. Ice the painful area for 15 to 20 minutes at a time. I would recommend using an ice pack several times per day if the pain is constant or is preventing you from participating in an activity. Ice immediately after activity.
- Posture – Having forward, rounded shoulders cause muscular imbalances in the shoulder and elbow. It decreases the ability of the scapular stabilizers to stabilize the shoulder joint. This causes the muscles at the elbow and forearm to work more. It also shortens the pectoralis major, pectoralis minor, and biceps and causes them to get tight. Stretching this area will make better posture more attainable. Below is a video showing how to stretch the pecs and biceps, and also how to use a wall to check your posture.
- Soft tissue mobilization – Soft tissue mobilization helps release the muscles around the forearm and decreases the pressure on the nerve. Use a massage ball, lacrosse ball, tennis ball, or your own fingers to massagepainful areas all around the elbow. Spend a good 3 to 5 minutes rolling. Do not roll so hard that you bruise the area, but it should be a pretty painful sensation. Roll out the area no more than a few times a week. See the video below.
- Supinator stretch – Stretching out the supinator will help decrease the compression on the posterior interosseous nerve. It is a good idea to perform soft tissue mobilization first because you will get a better stretch afterwards. Below is a video on how to stretch the supinator.
- Radial nerve flossing – You can mobilize the radial nerve to ensure that it is not entrapped in an area. Flossing will free-up the nerve if it is stuck and allow it to move along its pathway. Below is a video of radial nerve flossing.
- Thumb and finger strengthening – Strengthening the muscles in the thumb and fingers is important since PIN syndrome can affect these areas. Performing extension exercises is important for recovering hand strength. See the video below.
- Wrist strengthening – It is important to strengthen the wrist as well. PIN syndrome can affect wrist extension and ulnar deviation strength. Below is a video showing how to strengthen the wrist using resistance bands.
- Strengthen the rotator cuff and scapular stabilizers– Elbow injuries tend to occur because of weakness of the rotator cuff muscles and scapular stabilizers. These are the stabilizing muscles of the shoulder that allow the arm to reach, lift, and hold without injury or irritation. Using loop resistance bands and resistance bands can increase strength and difficulty.
In review
- The elbow joint is where the humerus, ulna, and radius come together.
- Movements of the elbow include flexion, extension, pronation, and supination.
- The supinator is a muscle just below the elbow.
- The radial nerve is one of the major nerves of the upper extremity. It begins near the armpit and travels all the way down to the hand.
- As it travels down the arm, the radial nerve will divide into superficial and deep branches at the level of the elbow.
- The deep branch turns into posterior interosseous nerve as it goes into the supinator muscle.
- The posterior interosseous nerve continues down the forearm to innervate the the muscles of wrist extension, finger extension, thumb extension, and thumb abduction.
- PIN syndrome is a compressive neuropathy of the posterior interosseous nerve.
- Symptoms come on gradually and include forearm pain and weakness in wrist and hand.
- Physical therapy is often successful in treating this condition.
- An orthopedist would be needed if the condition is not responding to physical therapy.
- There are things you and do.
- Rest
- Ice
- Posture
- Soft tissue mobilization
- Supinator stretch
- Radial nerve flossing
- Thumb and finger strengthening
- Wrist strengthening
- Strengthen rotator cuff and scapular stabilizers
As always, If you have questions about the content of this post or any other musculoskeletal questions, please e-mail me.
Additional resources
https://www.ncbi.nlm.nih.gov/books/NBK541046/
https://www.physio-pedia.com/Posterior_interosseous_nerve_syndrome