Overview of Peroneal Nerve Entrapment
Irritation and entrapment of the common peroneal nerve where it crosses the fibular head can be due to scar tissue, trauma, or other causes. One of the first things to do in the assessment of possible common peroneal nerve entrapment is to verify that the irritation in the common peroneal nerve at this location is not due to a lumbar spine cause, such as a herniated disk or spinal stenosis, and is truly localized to the common peroneal nerve itself.
Once it has been determined that the irritation of the common peroneal nerve is located at the fibular neck, one most commonly confirms this diagnosis on physical exam. The common peroneal nerve can be palpated where it crosses the lateral aspect of the fibula about 2 centimeters distal to the fibular head. In addition, about 3 to 4 cm proximal to this, it courses out from under the undersurface of the long head of the biceps femoris. Therefore, the nerve can usually be palpated in most patients by the examiner rolling the nerve under one’s fingers, where it crosses the lateral aspect of the fibular shaft.
When one elicits a positive response to palpation or rolling of the common peroneal nerve at this location, one would anticipate that it would reproduce a “zinging”-type sensation down the lateral aspect of the leg and over the dorsum of the foot (a positive Tinel’s sign). In most circumstances, there is no significant motor weakness, unless there has been a knee ligament dislocation or an injury to the posterolateral knee structures. In any event, one should perform a thorough physical exam to validate that the main motor structures innervated by the common peroneal nerve are still intact. This includes ankle dorsiflexion, EHL strength, total extension, and foot eversion strength.
As part of the evaluation for common peroneal irritation, is important to verify that the pain in this area is not due to other pathology such as biceps bursitis, tendinopathy or a sprain of the long head of the biceps at its attachment on the lateral aspect of the fibular head, a snapping biceps femoris tendon, a cyst of the proximal tibiofibular joint, or a lateral meniscus tear.
While we do recommend the use of an EMG/NCV as part of the workup to validate that the nerve irritation is coming from entrapment at the fibular head/neck region, it is actually very rare that these findings are positive on these studies. In effect, the main use of these neurology studies is to validate that the nerve irritation is not coming from a herniated disk or other spinal cause.
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(Please keep reading below for more information on this condition.)
Treatment for Peroneal Nerve Entrapment
Treatment of common peroneal nerve entrapment can include rest and observation, but when this is not successful a common peroneal nerve decompression can be performed. As is true for most nerve decompression surgeries, the success rate is approximately 70% to 75%. The most common reasons for continued symptoms after surgery are that the nerve may have permanent damage which cannot be regenerated, or a patient may have recurrent scar tissue develop even in the best of rehabilitation programs. Thus, we usually recommend that a common peroneal nerve decompression be performed after a thorough physical examination and assessment are obtained which validate that this is the correct diagnosis.
Peroneal Nerve Entrapment Injury FAQ
The common peroneal nerve crosses the lateral aspect of the fibula approximately 2 cm distal to the fibular head. It crosses within the peroneus longus musculature into the anterior compartment of the knee. At this location, it is relatively exposed to potential trauma and can either become irritated over time or it can become injured with sporting events such as being hit by a hockey stick, an opposing player’s shoe, or other devices. In addition, with posterolateral corner knee injuries, if the knee opens up significantly on the outside because of the posterolateral corner injury, the common peroneal nerve can become stretched as part of this injury and become irritated or damaged.
1. What is common peroneal nerve entrapment?
Common peroneal nerve entrapment is usually due to scar tissue in the region of the common peroneal nerve, which can lead to localized pain, numbness over the anterior and lateral aspects of the leg and foot, and weakness of the foot in dorsiflexion, toe extension, and foot eversion. This can be present in severe grades or it may be something that is only exacerbated by activity.
2. How can peroneal nerve compression be assessed?
One of the most important things to determine when one is looking at common peroneal nerve symptoms is determine if it is due to localized compression in the region of the fibular head or if possibly it is due to a herniated disc or a central spine problem. Once the spine or disc problem has been ruled out, a physical exam helps to document if there is common peroneal nerve entrapment present. Palpation of the nerve where it crosses the lateral aspect of the fibula can often reproduce the patient’s symptoms or cause some local irritation. Tapping on the nerve at this location, called a Tinel’s sign, may cause some zingers to go down the leg or cause numbness or weakness of the foot. Localized common peroneal nerve entrapment usually has these types of symptoms right at the location where the common peroneal nerve crosses the lateral aspect of the fibula.
3. What is peroneal nerve neuropathy?
A herniated disc or longstanding scar tissue around and entrapping the common peroneal nerve at the fibular head can cause some damage to the function of the common peroneal nerve. This includes the sensation over the lateral and anterior aspect of the distal leg and can also include weakness of the foot with dorsiflexion, foot eversion, toe extension, and great toe extension. This may include some mild weakness, but sometimes can even include a significant foot drop.
4. Where are the findings on EMG for peroneal nerve entrapment?
First off, it is important to ensure that the common peroneal nerve is not being irritated by a spine problem. When the spine problem has been ruled out, either by studies or by physical exam, then one can determine if there is some scar tissue that may be causing entrapment of the common peroneal nerve at the region of the fibular head. An EMG should be able to document this. Unfortunately, in mild cases of scar tissue entrapment at the fibular head, the EMG may not show any obvious areas of entrapment. In these cases, one must rely more on the physical exam and a positive Tinel’s sign to ensure that this is the location of the patient’s pathology.
5. What is the surgery for common peroneal nerve entrapment?
When the physical exam and/or studies document that the common peroneal nerve is entrapped in scar at the fibular head, a common peroneal nerve neurolysis may be performed. This involves making an incision over the anterior compartment of the leg and upper portion of the biceps femoris, developing a skin flap down to the region of the common peroneal nerve, and then gently releasing scar tissue along the nerve for a length of 6-8 cm. In addition, releasing any tight tissue of the peroneus longus fascia is an important portion of a common peroneal nerve neurolysis. At the time of surgery, one can often see areas where the nerve may be swollen, thickened, or showing less areas of blood vessels in it, which looks like a white scar-like region, which can document some localized areas of entrapment.
6. How often does a foot drop occur with posterolateral corner injuries?
In our series, about 15% of people will have a common peroneal nerve injury when they do have a complete posterolateral corner injury. In these cases, about 50% of the time the common peroneal nerve function will be restored. Therefore, it is important to have the patient wear an ankle foot orthosis and to work daily on stretching exercises so the heel cord does not become significantly tight if they have had a foot drop develop after a posterolateral corner injury.
7. What is the nonoperative treatment for common peroneal nerve entrapment at the knee?
The nonoperative treatment for a common peroneal nerve entrapment at the knee should involve avoidance of activities which caused it in the first place. In addition, avoiding those activities which cause any numbness or weakness of the foot to occur should be considered. If after several weeks the symptoms do not improve, then consideration may be necessary for a common peroneal nerve neurolysis, especially if there are any increases in numbness or weakness over time. This is because the ability for a nerve to recover is not predictable and any nerve changes could be permanent.
8. What is the recovery time after a common peroneal nerve decompression?
The recovery time after a common peroneal nerve decompression at the knee is usually 3-4 months. For the first 6 weeks, we do not want to encourage the knee to form a lot of scar tissue around the area of the decompression, so we have patients on crutches. We then slowly have them increase their activities starting at 6 weeks postoperatively, ensuring that there is no recurrence or increase in symptoms of the nerve irritation. For patients who do have a lot of numbness and weakness going into surgery, it can take months to determine if the common peroneal nerve function will be able to be restored. This is because the nerve often takes up to 4 weeks to start healing and then healing make take several months because it will heal at an average of a millimeter a day. Therefore to get down to the lower portion of the leg where the last muscle to return is the great toe extension could take multiple months.
9. What should one do if one wakes up with a foot drop after a knee replacement?
Foot drops after a knee replacement are often felt to be due to stretching of the nerve. Therefore, the knee should be immobilized in a bent position where there is less pressure on it to determine if that is the cause of the common peroneal nerve palsy. Close observation and possibly further studies should ensue based on the nerve recovery over time.
10. What is a splint that is used for a peroneal nerve palsy?
The best splint that is used for a foot drop is a plastic shell ankle foot orthosis. This will hold the ankle in a neutral position and prevent the foot from plantarflexing or pointing towards the floor. This is important because if the foot sits in that position for a long period of time, the heel cord can become tight and may require surgery to release this tightness alone.
11. What tendon transfers can be performed to treat a foot drop?
The most common tendon transfer that is performed via a foot and ankle surgeon is a re-routing of the posterior tibialis tendon through the middle of the ankle bones to the front of the foot. This can be effective in most patients to allow them to wean out of the use of an ankle foot orthosis. This decision should be made based on the degree of injury to the peroneal nerve and the time since the original injury to best assess if the nerve would recover or not over time.
12. What medicines may be useful to treat a peroneal nerve palsy?
If a peroneal nerve palsy occurs due to a trauma, such as a sporting instrument hitting the outside of the leg, or after surgery where retraction or stretching the nerve may have inadvertently occurred, the use of oral corticosteroids may help to stabilize the nerve and help it to recover sooner.