Sciatica

What Causes Sciatica?

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Most people with leg pain from a nerve are given a label. Fewer are given an explanation.

A diagnosis of sciatica is rarely accompanied by an explanation of what is actually irritating the nerve, why it developed, or what that means for recovery. Many people leave a consultation with a diagnosis but no map.

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Nerve-related leg pain is not a single condition. It is a symptom that can arise from several different sources. A lumbar disc prolapse and deep gluteal nerve irritation can produce almost identical pain running down the leg, and yet they respond to entirely different approaches. Treating one as the other is one of the most common reasons recovery stalls.

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People are often surprised by how inconsistent recovery feels. This page is intended to explain why.

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Written by

Dr Emma Collier

HCPC registration: PH153771

DPT (Doctor of Physical Therapy) | Moorgate (EC2)

Team Page

Reviewed by

Andrew Balderston

HMSc, HCPC, MCSP, AACP,

Clinical Director, Atherapy

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Likely source	Typical pattern
Disc prolapse (L5/S1)	Sharp or burning pain from the lower back through the buttock and outer calf to the heel. Worse sitting, coughing or bending forward. Often eased by walking or lying flat.
Disc prolapse (L4/L5)	Shooting pain from the lower back across the buttock to the outer shin and top of the foot. Weakness lifting the foot may be present.
Spinal stenosis	Aching or heaviness in both legs on walking. Relieves quickly on sitting or bending forward. Many patients find cycling far easier than walking.
Deep gluteal syndrome	Deep buttock ache radiating down the back of the thigh. Worse with prolonged sitting, driving or climbing stairs. Often no lower back pain at all.
Sacroiliac dysfunction	Buttock and upper leg pain, usually one side. Morning stiffness. Discomfort turning over in bed or rising from a chair.

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These patterns overlap. A full clinical assessment, not pattern-matching alone, confirms the source.

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The Sciatic Nerve

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The sciatic nerve is the largest nerve in the body. It begins in the lower back, passes through the buttock, and runs down the back of the leg to the foot. Several moving structures lie along that route, each of which can become a source of irritation, producing leg pain rather than back pain alone.

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Two types of fibre run within it. Motor fibres carry signals to the muscles; when affected, weakness develops. Sensory fibres carry signals back from the skin; when affected, they produce pain, numbness or tingling. Most people experience both.

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The nerve receives contributions from five spinal levels, L4 to S3. Irritation at different levels produces different symptom distributions, which is part of how the source is identified at assessment. Rankine (Clinical Radiology, 2004).

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Lumbar Disc Prolapse

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A lumbar disc prolapse, sometimes called a slipped disc or herniation, is the most common cause of nerve root leg pain in people under 60. Each disc has a tough outer ring and a gel-like inner core. Under sustained load or repetitive bending, small tears develop in the outer ring and the inner material pushes through, pressing against the adjacent nerve root.

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The L4/L5 and L5/S1 discs are most frequently involved because they carry the highest loads and move the most. Pressure on the L5 root produces symptoms along the outer shin and top of the foot. Pressure on S1 produces symptoms toward the heel and outer sole.

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People often arrive convinced they have permanently damaged their spine. Most haven't. The body treats prolapsed disc material as foreign tissue and gradually removes it. The body knows how to recover. What physiotherapy does is manage the nerve irritation while that process takes place.

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Dr Emma Collier PT, DPT, HCPC

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What the evidence says about disc prolapse

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Spontaneous reabsorption is the norm. - 90% of lumbar disc prolapses show measurable reduction on MRI within 12 months without surgery. Larger prolapses reabsorb at a higher rate than smaller ones. Chiu et al. (Clinical Rehabilitation, 2015).

Surgery and physiotherapy produce equivalent long-term outcomes. - At one and two years, outcomes are the same. The difference lies in speed of early symptom relief, not final result. Peul et al. (New England Journal of Medicine, 2007).

Active rehabilitation outperforms rest. - Structured exercise produces better outcomes than passive management. Fernandez et al. (British Journal of Sports Medicine, 2022).

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Lumbar Spinal Stenosis

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Stenosis is a gradual narrowing of the canal through which the spinal cord and nerve roots pass. Discs lose height, the small joints of the spine enlarge, and ligaments thicken into the available space. It is most common after 50.

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Walking becomes difficult. Standing produces heaviness or aching in both legs. Leaning on a shopping trolley brings relief. Many patients find cycling far easier than walking, because the seated, forward-flexed position opens the canal and reduces pressure on the nerve roots. Symptoms build on walking and resolve quickly on sitting. This is called neurogenic claudication, and it distinguishes stenosis from a disc prolapse, where sitting is often the position that makes things worse.

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Clinical Note

Stenosis and disc prolapse require opposite directional strategies in treatment. Stenosis responds to flexion-biased exercise and posture. Disc prolapse often responds to extension. Browder et al. (Physical Therapy, 2007); Lurie and Tomkins-Lane (BMJ, 2016).

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Deep Gluteal Syndrome

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The nerve can be irritated along its course through the buttock as well as in the spine. Several structures in the deep gluteal space can compress or tether it, not just the piriformis muscle, which is why the term deep gluteal syndrome has largely replaced the older label of piriformis syndrome in the clinical literature. Martin et al. (Arthroscopy, 2015).

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The symptoms closely resemble those of disc-related nerve pain: buttock aching that travels down the leg, often without any lower back pain at all. Months of spinal treatment directed at the wrong source is one of the most common patterns seen at initial assessment.

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"If someone has been told they have sciatica and has not improved after several weeks of treatment, the deep gluteal space is one of the first places we look. The spine is not always the source."

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Dr Emma Collier PT, DPT, HCPC

Can Sciatica Happen Without Back Pain?

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Yes, and it is more common than most people expect. Many people assume the pain must come with a back problem. In clinical practice, a significant proportion of patients present with leg pain, foot numbness or buttock aching as their only complaint.

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Deep gluteal syndrome irritates the nerve in the buttock, well away from the spine. Foraminal narrowing can compress a single nerve root at its exit point without involving the central canal. Spinal stenosis presents primarily as leg heaviness on walking, often with minimal back pain.

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Treatment designed primarily around the lumbar spine may be misdirected when the source lies elsewhere. Stynes et al. (British Journal of General Practice, 2018) found that clinical features, not symptom location alone, best predict nerve root involvement.

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Spondylolisthesis

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Spondylolisthesis is the forward slippage of one vertebra relative to the one below it. At L4/L5 or L5/S1, this narrows the space available to the nerve roots. The degenerative type develops as the joints and discs age; the isthmic type, more common in younger adults, results from a stress fracture in the vertebral arch.

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Most patients with low-grade degenerative spondylolisthesis respond well to physiotherapy. Surgery combined with physiotherapy has not been shown to produce better outcomes than physiotherapy alone at two years for low-grade cases. Forsth et al. (New England Journal of Medicine, 2016). Higher-grade slippage or progressive neurological deficit warrants surgical assessment.

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Sacroiliac Joint Dysfunction

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The sacroiliac joint can refer pain into the buttock, groin and upper leg in a pattern that closely resembles nerve root leg pain. A group of clinical tests, including the posterior shear, distraction and Gaenslen's tests, are used to distinguish sacroiliac origin from spinal pathology. A positive cluster strongly points toward sacroiliac origin and changes the treatment direction. Laslett et al. (Manual Therapy, 2005).

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Less Common Causes

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Foraminal Narrowing

Each nerve root exits the spine through a small bony opening. Age-related changes can compress the root as it passes through, sometimes without any central canal narrowing and often without significant back pain. Leg symptoms may be the only presentation.

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Epidural Fibrosis

After spinal surgery or significant disc herniation, scar tissue can restrict nerve root mobility. This is a specific cause of persistent or recurring symptoms in patients with a surgical history and is addressed in the post-surgery section of this resource.

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Inflammatory Conditions

Ankylosing spondylitis and related conditions can produce leg symptoms. Night pain, morning stiffness lasting more than 45 minutes, and systemic features should prompt specific investigation rather than standard physiotherapy management.

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One point that applies across all causes: worsening weakness in the leg, particularly if developing over days rather than weeks, should always be assessed promptly. It should not simply be waited out.

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When to seek emergency assessment

If you have any changes to your bladder or bowel, numbness in the saddle area (inner thighs or groin), or rapidly worsening weakness in both legs, go to A&E immediately or call 999. Do not wait for a physiotherapy or GP appointment.

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Where Symptoms Occur, and Why They Change

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The location and character of the pain help identify the source. The table below maps where each cause typically produces symptoms and whether one or both sides are usually affected.

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Region	Likely sources	One or both sides?
Lower back	Disc prolapse, stenosis, spondylolisthesis, sacroiliac joint	One side; occasionally both
Buttock	All causes; often the first area affected	One side (deep gluteal, disc); both (stenosis)
Back of thigh	Disc prolapse (S1), deep gluteal syndrome	One side
Outer shin, top of foot	Disc prolapse at L4/L5 (L5 root)	One side
Heel, outer sole	Disc prolapse at L5/S1 (S1 root)	One side
Both legs together	Spinal stenosis; rarely central disc prolapse	Both; warrants assessment

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Bilateral symptoms, both legs affected simultaneously, should always be assessed promptly. This pattern is most common in spinal stenosis but may in rare cases indicate central canal compromise requiring urgent attention.

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Pain and numbness also tend to move and shift over time. This is normal, and it carries useful clinical information.

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Centralisation is a positive sign. When symptoms move upward toward the buttock or lower back, nerve root irritation is typically resolving. It is one of the most reliable indicators of improvement. Donelson et al. (Spine, 1997).
Peripheralisation, symptoms spreading further down the leg, can indicate increased nerve load. It is worth reporting at the next appointment. It does not mean structural worsening.
Good days and bad days usually reflect changes in load: sitting longer than usual, an awkward night, a longer walk.
Shifting numbness is common as inflammation fluctuates. It does not mean a new nerve has been affected.

Any change in bladder, bowel or saddle-area sensation is different. See the red flags section.

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What People Often Fear

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Most people arrive at assessment carrying questions they have not felt able to ask. These are the ones that come up most often.

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"HaveI permanently damaged the nerve?"

Nerve root irritation, even when severe, recovers in the vast majority of cases. Permanent nerve damage from disc prolapse is uncommon. Most people recover fully with appropriate management.

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"Will this become chronic?"

Most cases resolve within three to six months. Fear of movement, not the severity of the physical finding, is the strongest predictor of prolonged recovery. Vlaeyen and Linton (Pain, 2000).

"Do I need a scan?"

Routine imaging is not recommended in the absence of red flag symptoms. MRI findings often include age-related changes unrelated to current symptoms. Clinical examination guides treatment more reliably. NICE NG59.

"Should I stop moving?"

Rest is associated with slower recovery. Graded movement, within tolerance, supports nerve healing and prevents the deconditioning that makes recovery harder. Complete rest is rarely helpful after the first day or two. Hagen et al. (Cochrane, 2010).

"Why do my symptoms keep moving around?"

Changing symptoms are normal as inflammation shifts and the nervous system adapts. Symptoms moving upward is called centralisation and is a reliable sign of improvement. Symptoms that move are not signs of new injury.

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Recovery Is Rarely a Straight Line

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Most people expect steady improvement. In practice, recovery tends to follow a gradual upward trend with setbacks built into it. People are often surprised by this. It does not reflect anything going wrong.

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A good week may be followed by two difficult days after a long meeting. A weekend away may set things back briefly. These are normal responses of irritated neural tissue to changes in load. The trend matters more than the day.

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When exercises are introduced, some increase in symptoms over the following 24 hours is expected. The question is whether they settle back to baseline, and whether the overall direction is improving over weeks rather than days.

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Clinical Note

Confidence tends to rebuild more slowly than the physical symptoms resolve. Patients often feel physically better before they feel ready to return to normal activity. Both timelines are real, and both are addressed in physiotherapy. Vlaeyen and Linton (Pain, 2000); Pinheiro et al. (Pain, 2016).

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Four Myths About What Causes Nerve-Related Leg Pain

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MYTH	REALITY
"I must have lifted something wrong."	Disc prolapse rarely has a single cause. It reflects cumulative mechanical load over time. One movement is almost never the whole story. Videman and Battie. Spine. 1999.
"My spine is crumbling. It will only get worse."	SDegenerative change is a normal part of ageing and does not predict pain or disability. Most people with significant MRI findings have no symptoms at all. Brinjikji et al. AJNR. 2015.
"I need to rest until it settles."	Bed rest is associated with slower recovery. Graded movement, within tolerance, supports healing and preserves nerve mobility. Hagen et al. Cochrane. 2010; Fernandez et al. BJSM. 2022.
"A scan will show exactly what is causing it."	MRI findings must be interpreted alongside clinical examination. Abnormal findings are present in people with no pain at all. The scan is one piece of information, not a diagnosis. NICE Guideline NG59. 2016 updated 2020.

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On imaging specifically: NICE does not recommend routine MRI for nerve-related leg pain. Brinjikji et al. (AJNR, 2015) found disc degeneration in 37% of asymptomatic 20-year-olds and 96% of asymptomatic 80-year-olds. An abnormal scan does not confirm the cause. A normal scan does not rule it out. Clinical examination remains the primary diagnostic tool.

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Vlaeyen and Linton (Pain, 2000) identified fear of movement as the strongest predictor of prolonged disability in spinal pain, stronger than the severity of the physical finding itself. Pinheiro et al. (Pain, 2016) found that psychological factors predicted long-term outcome more reliably than imaging or clinical findings alone.

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When someone understands that disc material reabsorbs, that nerve irritation settles, that the spine is built to load, their engagement with rehabilitation changes. And so do outcomes.

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Education is not supplementary. It is a primary clinical intervention.

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Clinical Case Study

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Case: Mark, 44, IT Project Manager

Mark arrived with a 9-week history of right-sided leg pain from the buttock to the outer calf, rated 7/10 on the NPRS. His GP had diagnosed sciatica and prescribed anti-inflammatories. He had been resting for six weeks, working from a recliner because sitting upright had become unbearable. He had started taking the lift at work because he no longer trusted the leg on the stairs.

He was convinced he had made things worse. A 15-minute walk two weeks earlier had increased the leg pain, and he had stopped walking entirely as a result.

At assessment, PSFS scores were: sitting at his desk 2/10, getting into his car 3/10, walking more than 15 minutes 4/10. Examination showed a positive straight leg raise at 45 degrees on the right, mild weakness of right extensor hallucis longus, and reproduction of leg symptoms with lumbar flexion combined with right lateral shift. Tests for the sacroiliac joint and deep gluteal region were negative. No saddle symptoms. No bilateral leg involvement.

L5 nerve root irritation from a right posterolateral disc prolapse at L4/L5. No imaging was requested, consistent with NICE NG59.

Mark was told that the worsening after walking was peripheralisation, a normal response to increased load, not structural damage. That explanation changed his relationship with movement.

At four weeks, after direction-specific exercises, nerve mobilisation and load management guidance: NPRS 3/10. PSFS: sitting 6/10, car entry 7/10, walking 6/10.

He described the improvement as the point at which he stopped thinking about the leg every time he stood up.

At discharge (11 weeks): NPRS 1/10. PSFS average 8.5/10. Mark had returned to his full working week and walking without restriction.

Six weeks of rest had delayed recovery rather than supported it. Identifying the correct source from the first session, and addressing his fear of movement alongside the physical treatment, was what turned things around.

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How Atherapy Identifies the Cause

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Identifying the source of these symptoms requires a systematic process. At Atherapy, assessment by Dr Emma Collier PT, DPT, HCPC combines a detailed clinical history, neurological examination, orthopaedic testing and nerve mobility assessment.

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A group of clinical tests, including the straight leg raise, slump test, femoral nerve stretch and sacroiliac provocation tests, are applied in sequence to arrive at a working diagnosis, not a verdict. Where that diagnosis is uncertain or not following an expected trajectory, it is revisited rather than assumed.

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"Two patients can present with identical leg pain and anidentical MRI. Their causes may still be different. Clinical examination tellsus whether the problem is primarily mechanical, inflammatory or neural, andwhether the spine, the hip, or both are involved. Getting that right from thefirst session is what makes treatment effective rather than generic."

Dr Emma Collier PT, DPT, HCPC

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Understanding your symptoms starts with identifying the source

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If you are living with persistent leg pain, numbness or nerve-related symptoms, assessment at Atherapy determines whether the problem is arising from the spine, the deep gluteal region, the sacroiliac joint, or somewhere else entirely. Accurate diagnosis changes treatment completely.

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Book a Sciatica Assessment

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Frequently Asked Questions

Key Evidence

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This page draws on the following primary sources.

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Brinjikji W et al. Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. American Journal of Neuroradiology. 2015.
Browder DA et al. Effectiveness of an extension-oriented treatment approach in a subgroup of subjects with low back pain. Physical Therapy. 2007.
Chiu CC et al. The probability of spontaneous regression of lumbar herniated disc. Clinical Rehabilitation. 2015.
Donelson R et al. Pain response to sagittal end-range spinal motion. Spine. 1997.
Fernandez M et al. Advice and exercise for sciatica: systematic review and meta-analysis. British Journal of Sports Medicine. 2022.
Forsth P et al. Surgery versus conservative treatment for degenerative lumbar spondylolisthesis. New England Journal of Medicine. 2016.
Hagen KB et al. Bed rest for acute low-back pain and sciatica. Cochrane Database of Systematic Reviews. 2010.
Laslett M et al. Diagnosis of sacroiliac joint pain. Manual Therapy. 2005.Lurie J and Tomkins-Lane C. Management of lumbar spinal stenosis. BMJ. 2016.
Martin HD et al. Deep gluteal syndrome. Arthroscopy. 2015.
NICE Guideline NG59. Low back pain and sciatica in over 16s. 2016, updated 2020.
Peul WC et al. Surgery versus prolonged conservative treatment for sciatica. New England Journal of Medicine. 2007.
Pinheiro MB et al. Psychological factors and long-term outcome in low back pain. Pain. 2016.
Rankine JJ. Lumbar disc disease and nerve root compression. Clinical Radiology. 2004.
Stynes S et al. Clinical diagnostic model for sciatica in primary care. British Journal of General Practice. 2018.
Videman T and Battie MC. The influence of occupation on lumbar degeneration. Spine. 1999.
Vlaeyen JW and Linton SJ. Fear-avoidance and its consequences in chronic musculoskeletal pain. Pain. 2000.

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