How your nerves may affect/cause Achilles tendinopathy

There’s a “silent” Achilles tendinopathy that has been baffling clinicians and researchers, because it seems to develop even in very sedentary people where there’s no overloading of the tendon to blame. We’re not entirely sure how this works, but it appears that your peripheral nerves, e.g. your sciatic nerve, may have something to do with it.

I say it’s a “silent” tendinopathy because these people usually don’t have any of the typical symptoms (like pain and stiffness) that we associate with Achilles tendinopathy in more active people. Interestingly, it is also this sedentary group of patients who are much more likely to rupture their tendons. Remember, if you need more help with an Achilles injury, you're welcome to consult one of our team via video call.

The terms tendinitis, tendonitis, tendinosis, and tendinopathy mean the same thing for all practical purposes, and we use these interchangeably in our articles.

In this article:

1. What causes a “silent” tendinopathy?

2. The role of increased neural tension

3. Do I need special tests for this?

4. How we can help

What causes a “silent” tendinopathy?

We’ve written a lot in the past about the causes of Achilles tendinopathy in runners, which include things like pushing your mileage too quickly, too many high intensity sessions, and not allowing enough recovery time. These types of training errors usually cause a reactive tendinopathy, where the tendon is very painful and irritated.

However, Achilles tendinopathies can also develop in sedentary people, and we’re not entirely sure about the cause in these cases. It appears that your peripheral nerves may have something to do with it. Your peripheral nerves in your legs run all the way from your lower back, down your legs and into the tips of your toes. One of the most well-known ones is the sciatic nerve.

Besides their more obvious functions of controlling your muscles and relaying information about sensation to and from the brain, your peripheral nerves in your legs also control the blood flow to various tissue types (tendons, muscles, bones, etc.) in your legs AND it influences the creation of new cells, restoration of injured tissue, and the inflammatory processes.

Studies done on animals have shown that an injury to a peripheral nerve can negatively affect the strength and quality of the collagen in the connective tissue (a rat's medial collateral ligament in this case) below the level of injury. It also appears that people who have had sciatica may be more susceptible to Achilles tendinopathy in future. What this suggests is that an injury to the nerves that supply your Achilles tendon may cause some of the degenerative changes that we see in tendinopathies.

But Webborn points out that most people with Achilles tendinopathy have never had a clear injury to a nerve like with sciatica – he suggests that there may be a more subtle cause for these “silent” tendinopathies.

The role of increased neural tension

Our nervous system is continuous from our brains to the tips of our toes. As we move our limbs, the nerves in our legs (the peripheral nerves) are meant to slide freely. Sometimes they can get a bit stuck, causing them to be compressed and to be stretched when we move. When this happens, we say that you have “increased neural tension” in your leg.

This compression can happen where the nerves exit the spinal canal or where they pass through tight muscles (in the buttocks for instance), and it is often of such a low level that you're not even aware of it. Webborn suggests that, although this increased tension in the nerves may not always cause you pain at the level of the compression, it may influence how well the nerve functions below that level and can therefore be partly or wholly to blame for why certain people develop Achilles tendinopathy.

And this seems to hold true with what we see in our patients. Some of our patients will be runners with no sign of increased neural tension and whose Achilles tendinopathy can be solely contributed to training error. Others will be sports people where the cause appears to be a combination of training error and increased neural tension. And then we also see patients who don’t do any running or jumping sports, but when tested, they display clear signs of increased neural tension.

Do I need special tests for this?

No. X-rays, MRI scans, and even nerve conduction studies cannot tell whether you have increased neural tension in your legs because the changes are too subtle. But the good news is that it can easily be tested through performing a simple movement test called the slump test.

When a physio gets you to perform the slump test, they will ask you to move your body in a certain way and then note your flexibility as well as how your symptoms change during the movement. It’s a standard part of our initial examination process that we use for all our online patients at TreatMyAchilles.com.

There's a demonstration of the slump test in this video:

We also always test our patients’ spinal mobility and gluteal/piriformis flexibility, because a stiff lower back and tight gluteal muscles can contribute to this problem. Your treatment plan will, more likely than not, include exercises aimed at improving your lower back’s flexibility and the ability of the nerves to move freely in your legs as well as your specific Achilles strength training programme.

How we can help

Need more help with your Achilles injury? You’re welcome to consult one of the team at TMA online via video call for an assessment of your injury and a tailored treatment plan.

We're all UK Chartered Physiotherapists with Master’s Degrees related to Sports & Exercise Medicine. But at Treat My Achilles we don't just value qualifications; all of us also have a wealth of experience working with athletes across a broad variety of sports, ranging from recreationally active people to professional athletes. You can meet the team here.

About the Author:

Maryke Louw is a chartered physiotherapist and holds an MSc in Sports Injury Management. You can follow her on LinkedIn, Facebook, Twitter, and Instagram.

References

1. Ackermann, P. W. (2013). "Neuronal regulation of tendon homoeostasis." International Journal of Experimental Pathology 94(4): 271-286.

2. Maffulli, N., et al. (1998). "Achilles tendon rupture and sciatica: a possible correlation." British Journal of Sports Medicine 32(2): 174.

3. Webborn, N. (2007). "A neuropathic model to the etiology and management of Achilles tendinopathy."