Common Conditions Explained: What Causes Sciatica?
Sciatica can cause pain, tingling, numbness or weakness that travels from the lower back or buttock into the leg. But sciatica isn’t really a diagnosis on its own - it describes a pattern of symptoms. Understanding why the nerve is irritated is an important first step towards managing it well.
In This Guide:
What sciatica actually means
Why the sciatic nerve becomes painful
How lumbar disc injuries can cause sciatica
The role of nerve irritation and inflammation
Can the piriformis muscle cause sciatic symptoms?
How sciatica is assessed
When scans may - or may not - be necessary
How sciatica is treated
When sciatic symptoms need urgent medical attention
The Story Begins:
It might begin as an ache in your lower back.
Then one morning you notice something different.
The discomfort seems to travel into your buttock. A few days later, you can feel it running down the back or side of your thigh. Perhaps your calf starts tingling, your foot feels slightly numb, or sitting in the car suddenly becomes uncomfortable.
Someone tells you:
“Sounds like sciatica.”
They may be right.
But there is an important question that still needs answering:
What is actually causing it?
Sciatica is not a single injury or disease. Rather, it is a term commonly used to describe symptoms associated with irritation or compression of the nerves that ultimately contribute to the sciatic nerve.
That distinction matters.
Two people can both say they have “sciatica” while the underlying reason for their symptoms—and therefore the most appropriate management—may be quite different.
What Is Sciatica?
The sciatic nerve is the largest nerve in the human body.
It is formed from nerve roots originating in the lower lumbar and sacral regions of the spine. These nerves join together within the pelvis before travelling through the buttock and continuing down the back of the leg, eventually branching into nerves supplying the lower leg and foot.
When one of the nerve roots contributing to this pathway becomes irritated or compressed, symptoms can be experienced along part of the nerve’s distribution.
These may include:
Pain travelling into the buttock, thigh, calf or foot
Pins and needles
Tingling
Numbness
Burning or electric sensations
Changes in sensation
Weakness in particular muscles
Some people experience considerable lower-back pain alongside their leg symptoms. Others have surprisingly little back pain and predominantly notice symptoms in the leg.
The exact location of symptoms can also vary depending on which nerve root is involved.
Importantly, pain travelling into the leg does not automatically mean that the sciatic nerve is damaged.
Nerves can become sensitive and irritated without being permanently injured.
For many people, symptoms improve considerably with time and appropriate conservative management.
One of the Most Common Causes: Lumbar Disc Injuries
Between each of the vertebrae in your spine sits an intervertebral disc.
These discs help distribute load and allow the spine to move.
A disc has a softer, gel-like centre surrounded by stronger layers of connective tissue. Like many structures within the body, discs naturally change over our lifetime.
Sometimes a disc can bulge or herniate sufficiently to affect a nearby nerve root.
This is one of the most common causes of sciatica.
Imagine a nerve root leaving the lower spine through a relatively small opening. If nearby disc material moves into this space, it may mechanically compress or chemically irritate the nerve.
The result can be pain or altered sensation travelling into the leg.
But there is an important misconception worth addressing.
A disc injury does not automatically mean a damaged spine.
Disc bulges and other structural changes are frequently seen on scans, including in people who have no pain at all.
Likewise, a disc herniation associated with sciatica does not automatically mean surgery will be required.
The body has a remarkable capacity to adapt and recover. In many cases, herniated disc material can reduce over time and the inflammatory response surrounding the nerve can settle.
This helps explain why many episodes of sciatica improve without surgery.
The scan is therefore only one piece of the puzzle.
Your symptoms, neurological examination, movement, strength and overall clinical presentation matter enormously.
Sciatica Is About the Nerve - Not Just the Disc
It is tempting to imagine sciatica as simply:
Disc presses on nerve = pain.
The biology is more complicated.
Mechanical compression can certainly play a role, but inflammation and chemical irritation around a nerve root can also contribute significantly to symptoms.
This helps explain why the relationship between what we see on an MRI and what someone actually feels is not always straightforward.
A relatively small disc change may be associated with significant symptoms in one person, while another person may have substantial structural changes on imaging with few or no symptoms.
Nerves are living biological tissues.
They need blood supply, space and the ability to move and adapt as we bend, walk and change position.
When a nerve becomes irritated, it may become more sensitive to movement or compression.
Activities such as prolonged sitting, bending, lifting, coughing or sneezing may temporarily aggravate symptoms in some people.
As the irritation settles, these same activities can often gradually be reintroduced.
The goal isn’t necessarily to permanently avoid movements that hurt.
It is to understand what is happening, settle the sensitive area and progressively rebuild tolerance.
What About Piriformis Syndrome?
The piriformis is a relatively small muscle located deep within the buttock.
The sciatic nerve travels through the deep gluteal region near the piriformis before continuing into the leg.
Because of this anatomical relationship, irritation or entrapment of the sciatic nerve around the deep gluteal region can sometimes produce symptoms resembling sciatica originating from the spine.
You may hear this referred to as piriformis syndrome.
However, there is an important distinction.
Sciatic symptoms originating from lumbar nerve-root irritation are considerably more common. Piriformis syndrome and other forms of deep gluteal nerve entrapment are alternative diagnoses that need to be considered within the context of the person’s complete clinical presentation.
Simply having a tight or tender piriformis muscle does not prove that it is compressing the sciatic nerve.
This is another reason assessment is important.
Pain around the buttock and leg can potentially originate from several structures, including the lumbar spine, hip, muscles, tendons and nerves.
The location of pain alone rarely tells the whole story.
So How Do We Work Out What Is Causing Sciatica?
A good assessment starts with listening.
Before testing strength or movement, your practitioner will usually want to understand the behaviour of your symptoms.
Questions may include:
* Where did the symptoms begin?
* Where do they travel?
* Is there numbness or tingling?
* Does the leg feel weak?
* What makes the symptoms better or worse?
* Is sitting difficult?
* Does walking change the symptoms?
* Do coughing or sneezing aggravate the pain?
* Have the symptoms changed over time?
* Have there been previous episodes?
The physical examination can then help build a clearer picture.
Depending on the presentation, this may involve assessing spinal and hip movement, muscle strength, sensation, reflexes and specific neurological or nerve-tension tests.
The objective isn’t simply to reproduce your pain.
It is to determine whether the pattern of symptoms is consistent with nerve-root involvement, identify any neurological changes and rule out other potential causes.
Do You Need an MRI?
Not necessarily.
This surprises many people.
If somebody has pain travelling down their leg, it can seem logical to immediately organise a scan to “see what’s going on”.
However, imaging is not routinely recommended for uncomplicated low-back pain or sciatica in the early stages.
Why?
Because scans frequently identify structural changes that may not actually be responsible for the person’s symptoms.
An MRI can be extremely useful when it is clinically indicated - but more information isn’t always better information.
Imaging becomes more important when serious pathology is suspected, neurological deficits are significant or progressing, symptoms are not improving as expected, or the results are likely to change treatment decisions.
In many cases, a thorough history and clinical examination provide enough information to begin appropriate conservative management.
How Is Sciatica Treated?
There isn’t one universal treatment for sciatica because there isn’t one universal presentation.
Treatment should reflect the individual.
For many people, early management involves helping them understand what is happening and finding ways to remain reasonably active without repeatedly aggravating the nerve.
Complete bed rest is generally not the answer.
Movement may need to be modified temporarily, but maintaining normal activity where possible is usually encouraged.
Treatment may involve a combination of:
Education and reassurance
Understanding that nerve pain can be extremely uncomfortable without necessarily representing serious or permanent damage can change the way someone approaches recovery.
Knowing what to temporarily modify - and what remains safe to do - can also reduce unnecessary fear and avoidance.
Movement and exercise
Exercise can be progressively introduced according to the person’s symptoms and capabilities.
Initially, this might involve finding comfortable movements and maintaining general activity.
As symptoms improve, rehabilitation may progress towards restoring spinal and hip movement, strength, trunk and lower-limb capacity, and confidence with everyday activities.
Manual therapy
Manual therapy may sometimes be used to help manage pain or movement restrictions.
Importantly, it should not be viewed as a treatment that physically “puts a disc back in” or permanently fixes the spine.
Current guidelines recommend that when manual therapy is used for low-back pain or sciatica, it should form part of a broader treatment approach that includes exercise and active rehabilitation.
Gradually rebuilding capacity
This is particularly important.
Feeling better is only one part of recovery.
If sitting, lifting, running, gardening or working has been difficult, rehabilitation should eventually prepare your body for those activities again.
That may involve gradually rebuilding strength, movement tolerance and confidence rather than simply waiting for all discomfort to disappear before moving normally.
Does Sciatica Ever Require Surgery?
Yes - but most cases do not automatically require it.
Specialist assessment may be appropriate when symptoms remain severe and disabling despite appropriate conservative management, or when significant neurological deficits are present.
Surgical decompression can be considered when non-surgical treatment has not adequately improved pain or function and imaging findings correspond with the person’s sciatic symptoms.
The decision is therefore based on much more than simply finding a disc bulge on an MRI.
When Sciatica Needs Urgent Assessment
Most episodes of sciatica are not medical emergencies.
There are, however, some symptoms that require urgent medical assessment.
Seek urgent medical attention if sciatic or back symptoms are accompanied by:
* New difficulty controlling your bladder or bowel
* Numbness around the saddle or genital region
* Significant or rapidly worsening weakness in the leg or foot
* Major neurological changes affecting both legs
* Symptoms following significant trauma
* Fever or systemic illness associated with significant back pain
* Other concerning symptoms suggesting serious underlying illness
These presentations are uncommon, but recognising them is important.
If you’re uncertain about a new or rapidly changing neurological symptom, seek medical assessment rather than waiting for it to settle.
The Bay City Health Takeaway
Sciatica can feel frightening.
Sharp pain shooting down the leg, numbness in the foot or sudden tingling can easily create the impression that something has been badly damaged.
But symptoms do not always tell us the whole story.
Sciatica is better thought of as a clue rather than a complete diagnosis.
The important question is not simply:
“Do I have sciatica?”
It is:
“Why is this nerve sensitive, and what does my body need to recover?”
For some people, the answer involves a lumbar disc and irritated nerve root. For others, the presentation may be influenced by different structures or conditions.
A thorough assessment helps separate these possibilities.
And once serious causes have been excluded, recovery is usually about more than simply trying to make the pain disappear.
It is about keeping you moving, gradually restoring the things your body currently finds difficult, rebuilding strength and capacity, and helping you return confidently to the activities that matter to you.
At Bay City Health, that is always the bigger goal:
Not simply treating a painful body part - but helping you understand your body, restore its capacity and keep it moving well.
References:
1. National Institute for Health and Care Excellence (NICE). Low back pain and sciatica in over 16s: assessment and management (NG59). Updated 2020.
2. Royal Australian College of General Practitioners (RACGP). Imaging in adults with acute low back pain. First Do No Harm: A Guide to Choosing Wisely in General Practice.
3. Jensen RK, Kongsted A, Kjaer P, Koes B. Diagnosis and treatment of sciatica. BMJ. 2019;367:l6273.
4. National Institute for Health and Care Excellence (NICE). Suspected neurological conditions: recognition and referral (NG127). Guidance regarding lumbar radiculopathy and neurological red flags.
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