All about Sciatica

 

Sciatica is a well-known term, but what does it mean?

We’re going to take a detailed look at the terminology, the anatomy, what goes wrong, and what patients can do to help.

 

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The word itself

 

The word sciatica tends to crop up in conversations when someone has leg pain that they think is related to their back.

Like lumbago, sciatica is an old-fashioned term, even mentioned by Shakespeare. But these terms are not necessarily used by clinicians, who require more specificity in how they name conditions.

When a patient feels pain in their leg, they might decide to call it sciatica when in fact it could actually be caused by: 

  • piriformis syndrome
  • a lumbar nerve root compression
  • referral from a hip joint or a joint in the spine
  • a hamstring injury
  • the list goes on…

Such vague use of a term isn’t unique in medicine. The terms “stroke” and “heart attack” are widely known and used by the public, but don’t really serve purpose in a clinical environment. Cardiologists and neurologists need more detail. 

So, when a patient says they have sciatica, any good clinician should recognise the breadth of conditions that this term might cover and put their thinking hat on to decipher what is really the matter. 

We mustn’t allow patients to be criticised for using the term, but instead, we should recognise that the word has different meanings for different people. Once we realise this, we can proceed with further conversation and investigation.

In essence, the word “sciatica” does not explain the cause of what is happening.

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What is happening?

As far as the general public are concerned, sciatica relates to pain more than anything else.

More worryingly, it seems to carry a kind of stigma, striking fear into people. It’s a loaded term:

  • “I’ve never been able to shift my sciatica”
  • “Poor you, my dad has sciatica too. He really struggles”
  • “Be careful lifting heavy items, you don’t want to get sciatica”

The fact that the term is loaded with such negativity is another reason, beside its non-specificity, that drives clinicians to avoid using it. Patients sometimes latch onto such terms and rely on any acquired knowledge of it to pre-determine their likely outcome. They’ve heard the worst and predict the same for themselves.

For example, if a patient knows someone with “sciatica” who has struggled for a long time, it will affect the attitude of that patient towards their own injury. They look at their friend’s experience and assume that they will face a similar journey. In fact, their friend might not have a condition that is at all similar, thanks to the broad sweep with which the term “sciatica” is used.

Sometimes the words we use can cause more damage than the injury.

You might be surprised that we’ve discussed this part of our topic first, but it is vitally important for patients and clinicians to understand the reality of what they’re saying.

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Anatomy first

 

Let’s look at the condition that clinicians would suspect is present if they were asked to define sciatica.

We need to look at the anatomy first, and in particular, the sciatic nerve.

We must start with the spine, which is made of vertebrae. One of the functions of our spine is to protect our spinal cord. Signals must pass from our brain to the rest of us, as far as our fingers and toes. Information also needs to flow in. Signals out and information in are passed through nerves.

Our spinal cord is the major conduit of nerves from our brain, reaching from the base of our skull to belly button level. It must then divide up so nerves can get everywhere they’re needed. They need to get to the tips of our fingers and toes, and also to all our internal organs.

To do this, bundles of nerves separate from the spinal cord and slip between the separate vertebrae to reach all the parts our body. These bundles are called nerve roots, and each one is numbered to match up to the vertebrae it passes between, like a good wiring diagram.

Each nerve root has defined tasks:

  • They send motor signals to a list of muscles which tend to perform a particular movement
  • They receive sensory information from a patch of skin

Clinicians have to memorise which nerve roots signal which muscles, which movements they trigger, and from where they receive sensation. They can then examine patients to work out which nerves are working, and which might not be.

But wait.

Sadly, a human wiring diagram isn’t just straight lines from the spine to the edges. We have some main nerves that act as mainlines for our arms and legs.

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Train tracks

The sciatic nerve is not a single nerve that exits the spine, but rather, it is the largest branch of the sacral plexus.

WHAT?!

Imagine a train station, a terminus like Paddington.

  • Nerve roots are the platforms in the station. Each with a number.
  • The plexus is the criss-crossing of tracks as the they leave the platforms so trains from any platform can go to any destination.
  • A nerve branch is the main line. Lots of trains share it.
  • Main nerve branches split up into smaller branch lines as they get further away from the spine (the terminus with its nerve roots) and head to individual towns, or in our case, to the calf, heel, shin, foot and toes.

The sciatic nerve is made of nerves from the roots L4, L5, S1, S2 and S3. These nerves leave our spine, and by the time they’ve reached your buttock, they’ve passed through the plexus where their signals can cross tracks a little and collected themselves together to form the sciatic nerve.

The sciatic nerve passes down the back of your leg, between your hamstring muscles, about the width of your thumb. When it gets near to your knee, it makes its first big divide, sending a branch down the back of your calf and under your heel to the sole of your foot, and sending another around the outside of your lower leg and down to the top of your foot.

That’s enough detail for now…

With an idea of the anatomy, we can look at what happens when nerves are working and when they’re injured.

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Examining nerves

 

A clinician who suspects a case of sciatica will want to test the nerves involved. It will either support the theory that there is a nerve condition to manage or rule it out and raise the possibility of there being a different problem. To test a patient’s nerves, clinicians perform a neurological exam.

It’s important that these examinations are done, as patients often haven’t noticed symptoms such as areas of numbness, or slight weakness. They won’t have reported them to their clinician, and the clinician will perhaps be unaware of their presence until performing an exam, that is IF they perform an exam!

Here’s what they look for: 

  • The skin can be touched either lightly or with a sharp object to see if the patient is getting the right sensation – i.e. signals are being sent up the relevant nerve to the nerve root, and up the spinal cord to the brain. The areas that relate to a particular nerve root are called dermatomes.
  • Movements can be tested to see if the correct muscles are being engaged – i.e. the brain is sending messages out to the right muscles. The movements that relate to a particular nerve root are called myotomes.

  • Reflexes are another useful test – checking the presence of a message that passes from sensory nerves across to motor nerves in the spinal cord without our brain having to get involved.
  • Nerves can also be tensioned or stretched gently, to see if this reproduces the patient’s pain.

With all this tested, a comprehensive picture of nerve function can be put together and used to develop an understanding of a patient’s condition.

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When nerves go wrong

Injured nerves can do various things. Instead of performing normally, they can produce positive or negative faults:

“Positive” faults are when we get more signals than normal:

  • An increase to sensation – either pins and needles, the presence of extra signals above what is normal, or even hypersensitivity, when gentle contact is perceived as painful.
  • Motor function can also increase, most often seen as a flickering or fasciculation of the muscle being signalled.

“Negative” faults are when we get fewer signals than normal:

  • A loss of sensation, leading to numbness. There can be partial loss first.
  • Motor function can be lost, leading to weakness and paralysis.

The use of the words "positive" and "negative" in the context of nerve faults doesn't correlate to the severity or desirability of the symptoms. It just describes the current status of nerve function - either more happening than normal or less. "Positive" nerve faults might, in fact, create a worse experience than "negative" faults. 

Some patients can experience a mixture of "positive" and "negative" faults, and the combination of these can result in seemingly odd symptoms. Limbs can feel “woolly”, “tingly”, or there can be an altered sensation of temperature, perhaps hot or cold. When we really look in detail, we see that different nerve endings report different sensations such as temperature or vibration. When these get confused, it tells us about the wiring in the spinal cord, which we will leave for another day.

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Categorising nerve injuries

 

Just to be technical for a minute, let’s break nerve injuries into different categories. 

  • Some nerve injuries leave patients in pain, but with unaffected sensation, and full motor capacity. If we expect that the injury has started from the nerve root, we call this radicular pain.
  • At the other end of the spectrum, a radiculopathy is where the nerve isn’t functioning properly. There is a loss of full power and/or sensation is affected. This can often occur without any pain.
  • As if that wasn’t confusing enough, we also talk about nerve mechanosensitivity, which is where a nerve is irritated by movement.

To bring us back to the beginning of this exploration of the term sciatica, we began by talking about the pain that people feel. Besides the errors of movement and sensation we’ve described, nerves can also be painful. Bloody painful.

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Nerve pain

The pain from nerves is different in its mechanism from what people might typically think of as pain.

Pain is an impenetrably complex subject, but one of the starting points is that there are three types of pain: nociceptive (the normal pain we all think of), central sensitisation (definitely for another day), or the type that nerves get to own: neuropathic, with conditions that are sometimes called a neuralgia.

Such examples are:

  • Trigeminal neuralgia – a condition that affects the trigeminal nerve which operates the muscles across our face
  • Cluster headaches – a particularly nasty form of headache
  • Toothache - often be related to nerve damage

In the domain of back pain, we see sciatic nerve injuries quite often, and are thankfully spared from dealing with the other conditions mentioned above.

The pain can feel like a burning, or sometimes, an electric-shock type of pain.

The different nature of neuropathic conditions compared to nociceptive pain means they can be absolutely constant without any periods of remission. There is often no relief in any position, so lying down won’t make it go away, nor might it subside at night.

Without wanting to be too morbid, it’s worth knowing that people interviewed for research about their experience of severe cases of sciatica have said things like 

  • “this was worse than I imagined pain could be”
  • “I was reduced to the state of a screaming animal”
  • “If there was a gun at the side of the bed, I’d have sooner shot myself”

Thankfully, not everyone experiences injuries that are this extreme.

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The challenge of treatment

 

Understandably, given the unremitting nature of such conditions, it can be hard to make progress using manual therapy alone. If every position hurts, and the pain never stops, techniques to stretch muscles and loosen joints are less likely to be satisfactory.

Instead, injections and surgery are more likely to offer a solution for tough cases of neuropathic pain, depending on the contributory factors. It is for this reason that such interventions are better supported by decision-makers than they are for low back pain on its own. However, the risks of surgery in particular means that they typically aren’t used until other interventions have been tried.

Medications are also inconsistent:

  • Common painkillers don’t have much impact as they are designed to deal with different (nociceptive) pain mechanisms.
  • Anti-inflammatories will only contribute if an area of inflammation in the body is causing the nerve injury, but they won’t particularly help the injured nerve itself.
  • Other medications such as gabapentin and pregabalin are designed to help neuralgic pain, but the effects we see in clinic vary from person to person.
  • Steroids in the early days of nerve injury are perhaps effective.

Far from being an afterthought, education is very useful for patients and highly effective. It definitely helps a patient if you explain to them 

  • the nature of their injury
  • the reason their pain behaves as it does e.g. is constant, or in other cases varies from position to position
  • why they can have a functional deficit (loss of power or sensation) but no pain
  • why their pain is caused by an injury elsewhere

It’s also important to encourage activity. Many forms of exercise and activity are very tolerable. There is likely to be discomfort during and after the activity, but making sensible decisions about what to do will hopefully leave a patient at very low risk of exaggerating the injury. At the same time, the benefits of engaging in activity, both physically and socially cannot be underestimated.

Disappointingly, conditions such as these often take some considerable time to settle down. There is often little improvement in the first few weeks, and at 12 weeks only about 50% of people have had a significant improvement. By 12 months, around 25% of people might still be experiencing symptoms.

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The reality of living with nerve injuries

 

Well done for getting this far. There’s plenty of knowledge to take aboard about what nerves are, what they do, where they are, and how they go wrong 

Time to bust some myths.

 

MYTH 1: Nerve injuries are not all about compression

People think that all nerve injuries are defined as a “trapped” nerve. It’s not true, and is an unhelpful belief, as it often resigns people to the expectation that surgery is required.

To some patients’ disappointment, an MRI might strongly suggest that their nerve is being physically trapped, but when they recover from “successful” surgery they find that symptoms persist while the MRI findings have been dealt with. The supposed physical compression of the nerve tissue wasn’t really the cause of the injury 

As well as being triggered by compression, nerves can also be irritated by other factors, such as:

  • Leakage of nuclear material (not radioactive, but from the centre of an intervertebral disc) which causes a large inflammatory reaction
  • Inflammation from spinal joints, particularly arthritic ones
  • Mechanical deformation – being twisted or tensioned

 

MYTH 2: It’s not all about slipped discs…

…because discs don’t slip. Simple as that. They can be injured, push outside of their typical margins, but they don’t slide around. They are fused to the bones. They can become inflamed, but they definitely don’t swell up like a twisted ankle.

Having said that, severe disc protrusions can definitely cause a compromise to nerve function, as they can press on the nerve root strongly enough to cause permanent damage.

This is particularly dangerous at the base of our spine where nerves leave the spinal cord to manage our bowels and bladder. If these nerves are compromised, there can be changes to bowel or bladder control, and this can be permanent if not dealt with. These cases, known as cauda equina syndrome, are a medical emergency, and it is for this reason low back pain patients are routinely asked about bowel and bladder function.

 

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What to do?

 

Here are some take-home messages for people with nerve pain.

Absorb as much of the information above as you can. Patients who know more, do better.

Appreciate that nerve injuries are often the result of another injury. If you do everything you can to calm the original injury, you’re giving the nerve injury the best possible environment to settle.

Understand that nerve injuries constitute a unique category of pain, so don’t worry if your typical remedies don’t help.

Consider that your nerves are irritated. They are pissed off, as you are.

The problem is one of sensitivity. Your goal is to reduce the sensitivity of the nerve. Find what the nerve is sensitive to and try to avoid those activities until the condition settles.

There can be simple interventions that really help. These can be hard to predict however so you must seek help. Hopefully, a good clinician can help you understand the extent and nature of your injury and identify any contributory factors. Try the techniques they give you carefully. They might not be what you would think of, but you must engage in the problem.

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Some useful links

 

Tom Jessom is a physio with a special interest in all things sciatic. His website is full of great information and covers his research into sciatic conditions: https://tomjesson.com/

Living Well with Pain is a website written by a patient called Tina who has lived the full experience of sciatic pain: https://livingwellpain.net/

Here is a video explanation on Youtube by FisioCamera: Click here

This is an excellent resource put together by South Tees Hospitals:
South Tees NHS Trust Sciatica Booklet

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