One challenge I come across as a practicing physiotherapist is the vast number of possible sources of pain and dysfunction. A foot may be a foot, but often–because the foot is connected to the lower leg, knee, and hip–a foot problem may arise from a hip issue. Moreover, because the nerve that supplies the foot runs the entire length of the body, literally from head to toe, foot pain may come from the spine! Indeed, a full 10 to 20% of runners with foot pain have an issue stemming from a nerve.
Nerve pain is far more common than we, as runners or medical professionals, realize. While it’s more common to overuse or strain a muscle or tendon, or if we fall, possibly break a bone, irritating a nerve is not only possible but perhaps even commonplace amongst trail and ultramarathon runners. This may be because of the extreme demands we place on our bodies and also because of our propensity for falling. Falling might bruise a muscle or bone, but it can also irritate a nerve.
This article outlines the signs and symptoms of nerve pain: how and why it happens, and how we can go about properly treating it.
What is Nerve Pain?
Nerve pain, or neurogenic (of nerve origin) pain, can arise any time a nerve is sensitized. Under normal circumstances, a nerve is quite robust and asymptomatic when exposed to mild to moderate pressure and/or stretch. However, once a nerve is irritated, it can be very sensitive to any compression, stretch, or chemical changes (even our own, internal stress hormones). This often results in neurogenic pain.
There are generally two types of nerve sensitization, mechanical and chemical sensitization:
This occurs any time the normal motion and position of the nerve is restricted. While this could be a severe pinch (say, from a vertebral disc), the vast majority of mechanical restrictions are far more subtle and related to stiffness of surrounding muscles, tendons, joints, and fascial (connective) tissues.
Moreover, mechanical stress may involve overstretching a nerve. In general, nerves are very sensitive and resistant to stretching (and under normal circumstances, have enough length so they, themselves, don’t need to actually stretch). Thus, any force (whether accidental or intentional) that overstretches a muscle, tendon, or joint might also overstretch–or even strain–a nerve!
This occurs from some sort of inflammatory chemicals that come in contact with a nerve, possibly from an injury adjacent to a nerve (like a strained muscle or broken bone).
Where and Why Nerve Pain Occurs
There are two other important things to note about neurogenic pain.
First, the nerve can create pain anywhere along its length. It may surprise even the educated runner to know that a sensory nerve unit in the foot has but three parts: the peripheral nerve (which in a tall male could be four feet long), a tiny interneuron in the spinal cord, and the upper nerve (which runs the length of the spinal column and into the brain). As such, any sensitivity anywhere along that sensory (or motor) unit can cause pain anywhere above or below that nerve! It may be mind blowing to consider that a stiff neck could be causing your foot pain, but it is both possible and far more common than anyone (including the sports-medicine professional) may realize.
Second, nerve sensitivity is cumulative. Because a nerve runs the length of the body, there are countless areas where the nerve might come under irritation. A good analogy for this is a garden hose: a single small crimp in the hose may result in no perceptible difference in flow. But two or three crimps anywhere along the length of the hose often results in major interruption. The nerve functions in the same way: sensitivities anywhere along its length–at the neck, mid-back, low back, or pelvis–can cause a mild compression at the foot and ankle to result in severe pain.
Signs That Your Running Injury is Nerve Pain
Here are six signs that your running injury is actually nerve pain:
1. Your Pain Fails to Respond to Conventional Treatment.
If conventional sports medicine treats injuries to muscles, ligaments and tendons, and bone, then conventional treatment often includes RICE: Rest, Ice, Compression, Elevation. This is the standard treatment for acute injuries; however, it (at least the RI) is often used for chronic injury as well. Resting and icing chronic plantar-foot and Achilles pain continues to be prudent and useful for prolonged, subacute issues.
Sports physical-therapy treatment for orthopedic injuries also includes stretching and strengthening. For healing soft tissues, this stress-and-rest cycle, when patiently and progressively applied, nearly always results in progressive improvements–if the injury in quest is muscle, tendon, or bone!
However, if your pain is neurogenic, then conventional treatment rarely, if ever, is effective, for two reasons:
- There is no soft-tissue injury (to rest, ice, stretch, and strengthen).
- The sensitive nerve needs very specific (and often very gentle) treatment.
Not only that, but conventional orthopedic treatment–namely aggressive stretching, massage, icing, and compression–could make nerve pain worse by overstretching, compressing, or otherwise irritating an already sensitive nerve.
Lastly, rest alone seldom improves nerve pain. The reason is simple: if there is a mechanical restriction of the nerve (either in the painful area or anywhere along its length), passive rest will not free the restriction and restore motion. Pain may subside with rest, but nearly always returns with the resumption of running or other activity.
2. Your Pain Includes a Dull Ache, Pins and Needles, Tingling, or Numbness.
Orthopedic pain is nearly always tied to activity, and symptoms will be experienced during activity (such as running, hiking, walking, or standing), and the symptoms are fairly consistent, ranging from tightness and stiffness, to a dull ache or sharp, stabbing pain.
Conversely, nerve pain–which can replicate those aches and stabs–often includes other abnormal symptoms. Pins and needles, tingling, and numbness are classic neurogenic symptoms, and seldom (if ever) arise from an orthopedic injury. That said, nerves can also replicate dull-ache, tight, or stabbing symptoms. What differentiates a painful nerve from the muscle and tendon is outlined below.
3. Your Pain is Extremely Variable and Disproportionate to Activity Level.
Another sign of neurogenic pain is inconsistency in pain behavior. Soft tissue pain–both acute and chronic–has a predictable pattern:
- Stiff and sore with initial activity (first thing in the morning, after prolonged rest)
- Generally warms up with small amounts of activity
- At some point, will worsen with too much activity
This is the classic pattern for muscle and tendon pain, such as Achilles or plantar-fascial irritation.
However, nerve pain can be maddeningly variable and difficult to predict: a 30-minute jog may feel fine one day, then another day, the same jog (route, pace) may result in a major flareup. Or, aggressive (but variable activity) such as a technical trail run (or a multi-directional running sport, such as ultimate frisbee) may feel okay, but a half-hour flat walk could be quite painful.
Additionally, another hallmark of nerve pain is variable location. Whereas something like plantar fasciitis has extremely focal symptoms (often at the base of the heel, near the anterior/medial aspect), nerve pain can wildly vary in location, often hopping around from one end or side of a bone or joint to the other. This is likely due to the nerve referring symptoms to the various locations of its innervation.
4. It is Difficult (or not Possible) to ‘Feel’ Your Pain.
Another hallmark of most orthopedic injuries is the ability to palpate (touch, massage, or otherwise locate) the precise area of sensitive tissue. Again, with classic Achilles and plantar-foot pain, there is nearly always a precise area of sensitivity: the location of strained, sensitive, and healing tissue that, when touched, often results in significant pain replication, sensitivity, or, when hotly acute, might send you jumping!
Nerve pain is often elusive. Regardless of how sharp, stabbing, or severe its intensity, many runners may be unable to find the precise area of injury or irritation. They themselves may poke or massage the area, or even get soft-tissue mobilization from a physio or massage therapist, but no one is able to actually pinpoint the sensitive area. This is likely because the pain in question is being referred to the area, from a sensitive area farther away. For nerve pain, this could be anywhere along the length of that nerve: farther up the leg, or in the hip, pelvis, back, or even in the neck.
5. You Have Pain at Rest.
If there is one hallmark sign of neurogenic pain, it is pain at rest. Unless extremely acute, orthopedic injury will not be painful at rest: namely sitting or lying down. Indeed, only if a runner has incurred a severe hamstring strain (resulting in swelling and bruising–which is rare) will they experience pain with sitting.
Conversely, a sensitive nerve often refers pain at rest. Why this occurs is variable (and not completely known); suffice to say that when a nerve is sensitized, several factors can create pain at rest, including:
- Compression stress (in sitting, on the sciatic or obturator nerves)
- Postural stress (usually sitting, but any position, due to nerve stress related to spinal position)
- Restorative healing (as nerves will often try to heal themselves at times of rest)
Symptoms at rest is major red flag for nerve pain and should be considered a strong sign that your running pain is not a simple orthopedic injury.
6. Diagnostic Imaging Fails to Find Any Pathology.
When an injury fails to improve, most runners (and their sports-medicine professionals) will seek out diagnostic imaging in order to help identify the source of the injury and (ideally) why it fails to improve. So it can be a crushing blow to both runner and doctor when that imaging–often an MRI–fails to find any pathology at all. Especially in the case of severe, unremitting pain, how can that be?
Nerve sensitivity very often fails to show anything on diagnostic imaging because:
- A sensitized nerve will not demonstrate any visual abnormality. Sometimes, mild swelling may occur around the sensitive nerve, but so long as the nerve is intact (not severed), no abnormality will be seen and the painful area often looks perfectly normal.
- Pain may be referred from far away, out of the view of the imaging. An impinged nerve in the low back may not even appear in a lumbar scan, and certainly won’t appear in imaging studies of a foot and ankle, yet the low back is a common location of nerve sensitivity for the foot nerves.
So unless there is a blatant source of nerve impingement (where a tendon or other tissue may be seen, compressing a nerve), diagnostic imaging will fail to find the source.
More scary, therefore, is the prevalence of ‘false positives.’ These occur when a runner is experiencing neurogenic pain (either locally or peripherally from a sensitized nerve), but the imagining shows “mild arthritis,” “degenerative changes,” or other rather mild tissue wear and tear, which is falsely interpreted as the source of the pain. This often leads runners and doctors alike to rush into surgery to repair or clean up the area. Unfortunately, not only do these procedures fail to improve the symptoms, but they can often worsen them by creating additional scar tissue, mobility loss, or general post-operative sensitivity.
Common Running Pains and Possible Nerve Sources
Here is a short (but hardly exhaustive) list of common running-injury areas and the possible origin of neurogenic pain:
|Injury/Area||Possible Nerve Involvement|
|Posterior pelvis, hip (butt)||Cluneal, sciatic, obturator nerves|
|Anterior and lateral hip and thigh||Cluneal, sciatic, lateral femoral cutaneous nerves|
|Medial thigh and knee||Femoral, obturator nerve|
|Lateral shin||Superficial fibular nerve|
|Medial shin||Tibial nerve|
|Lateral ankle||Sural nerve|
|Medial ankle||Tibial nerve|
|Plantar foot||Medial and lateral plantar nerves|
|Dorsal (top of the) foot and toes||Superficial, deep fibular nerves|
How to Treat a Nerve-Pain Issue
This can be complicated–and is best left to highly trained professionals–but it is possible to treat a sensitive nerve. And when done carefully and skillfully, neurogenic pain can often improve rapidly. Some recommendations:
Think Like a Plumber (or Electrician).
While this somehow is baffling to an orthopedic professional, it is common sense a plumber: you must address the full length of the ‘cord’ (or pipe). Normal, healthy ‘flow’ requires the entire length of the nerve be free and clear from restriction or stress. This may include treatment of the spine (or even cranium) to get full resolution of pain.
Sensitive nerves even when freed may still be sensitive. Once a nerve is even mildly irritated, it can take a very long time for that irritation to heal. Some texts believe that it could take a week per centimeter of nerve length for a severe nerve injury to heal (which is often why severe nerve compression from neck and back injuries can take a year to fully heal).
For severe nerve pain, be very patient in return to activity. The goal should not necessarily be a full abolishment of pain, rather a progressive decrease in frequency, intensity, and duration of symptoms.
Sensitive nerves heal best with gentle, frequent mobility and lots of blood flow. It is said that the nervous system is only 20% of the body’s mass, yet it ‘consumes’ 80% of its blood flow. Thus, gentle, frequent activity will not only help gently move the nerve, but also supply vital restorative blood flow–both factors that will result in the fastest possible healing.
In conclusion, just because you’re a runner doesn’t mean your injuries will only occur with muscles, tendons, and bones! Be aware of the importance of healthy and mobile nerves, know the possible causes and symptoms of nerve sensitivity, and, if you think you could have nerve pain, seek out comprehensive treatment from a ‘systems professional’–preferably one who thinks like a plumber or electrician!
Call for Comments (from Meghan)
Have you been diagnosed with a nerve injury? If so, what was the diagnosis? And where did you actually feel pain?