Sciatica: Causes, Diagnosis, and How Doctors Decide What Comes Next
Sciatica is pain, tingling, numbness, or weakness that travels from the low back or buttock into the leg because a nerve is irritated — most often by a lumbar disc herniation or spinal stenosis.
In my practice, sciatica is a starting point, not a complete diagnosis. The real question is which nerve is irritated, and why.
What Is Sciatica?
Sciatica is a symptom pattern, not a single diagnosis. It usually means pain that starts in the low back or buttock and travels down the leg — into the thigh, calf, foot, or toes.
It can feel like:
- Sharp, electric, burning, or shooting pain
- Tingling or numbness
- Leg weakness
Some people feel worse with sitting or bending, others with standing or walking, and some notice pain when coughing or sneezing.
The word is often used casually for any leg pain, but not all leg pain is true sciatica — which is why the specific nerve and cause matter.
A nerve is a cable that carries signals between your spine, brain, and body. A nerve root is the part that leaves the spinal canal near the spine. The spinal canal is the main tunnel where nerves travel.
The Most Common Causes of Sciatica
Sciatica most often comes from irritation of a nerve in the lower back, or lumbar spine.
Lumbar Disc Herniation
A lumbar disc herniation is when the soft inner part of a spinal disc pushes out through its outer layer. (A spinal disc is the cushion between two spine bones.) It can cause sciatica two ways: by pressing on a nerve root, or by triggering inflammation — swelling and irritation — around the nerve.
This usually happens at L4-L5 or L5-S1, the disc spaces in the lower spine. L4-L5 is the level between the fourth and fifth lumbar bones; L5-S1 is between the fifth lumbar bone and the sacrum at the base of the spine. Disc-related sciatica often travels below the knee and feels worse with sitting, bending, coughing, or sneezing.
The finding matters most when the herniation is touching or compressing the nerve that explains the patient’s pain pattern.
Learn more: Lumbar Disc Herniation: A Surgeon’s Patient Guide
Lumbar Spinal Stenosis
Lumbar spinal stenosis means narrowing around the nerves in the lower back. It can come from:
- Arthritis (joint wear and inflammation)
- Thickened ligaments (the bands of tissue that support the spine)
- Loss of disc height
- Bone spurs (extra bone growths)
- Spondylolisthesis (one spine bone slipping compared with another)
Stenosis often causes leg pain, heaviness, numbness, or cramping with standing or walking, and relief with sitting or leaning forward — such as over a shopping cart. This walking-related pain is called neurogenic claudication: leg symptoms from nerve crowding in the spine during standing or walking.
Learn more: Lumbar Spinal Stenosis: A Plain-Language Guide for Patients
Foraminal Stenosis
The foramen is the side exit tunnel where a nerve leaves the spine; foraminal stenosis is narrowing of that tunnel. It can irritate one specific exiting nerve, causing pain, numbness, or weakness in that nerve’s pattern.
This is a common place where MRI reports sound scary. What matters is whether the narrowed foramen is on the same side as your symptoms and at a level that fits your pain.
Spondylolisthesis
Spondylolisthesis is when one vertebra (a spine bone) slips slightly relative to another. The slip can narrow the spinal canal or foramen and irritate nerves, causing sciatica-like leg pain. The degenerative type, related to aging and arthritis, is common at L4-L5.
Learn more: Spondylolisthesis: When the Bones Slip
Less Common or Non-Spine Causes
Not every buttock or leg pain starts in the spine. Other causes include:
- Piriformis syndrome or deep gluteal syndrome — a nerve irritated deep in the buttock
- Sacroiliac joint pain — from the joint between spine and pelvis
- Hip problems, such as arthritis or tendon irritation
- Peripheral neuropathy — nerve damage outside the spine
- Vascular claudication — leg pain from poor blood flow
- Infection, tumor, or inflammatory conditions
Learn more: Sacroiliac Joint Dysfunction: Why It’s Often Missed
Planned future topic: Piriformis syndrome
What Sciatica Feels Like: Symptom Patterns Matter
The path of pain gives clues, not a final answer by itself.
Pain Location Can Suggest Which Nerve Is Involved
Doctors compare your symptoms with common nerve patterns:
- L4 nerve: pain or numbness toward the front of the thigh or knee, sometimes with weakness in the quadriceps (front thigh muscles).
- L5 nerve: pain or numbness along the outer leg or top of the foot, sometimes with trouble lifting the foot or big toe.
- S1 nerve: pain or numbness down the back of the calf or outer foot, sometimes with calf weakness or a reduced ankle reflex. A reflex is an automatic muscle response tested with a small tap.
These maps help but aren’t perfect — real symptoms often overlap, so a doctor matches these approximate patterns against exam and imaging before deciding which nerve is involved.
Why Back Pain and Leg Pain Are Different Clues
Sciatica means leg symptoms are a major part of the problem; back pain alone is not sciatica. Many people have both. The dominant symptom matters: if leg pain is much worse than back pain, doctors look harder for nerve irritation. If back pain dominates, the treatment path may differ.
Why MRI Findings and Symptoms Must Match
An MRI — magnetic resonance imaging, a scan showing discs, nerves, bones, and soft tissues — may list many findings. But a finding only matters if it fits the clinical picture:
- A left-sided disc herniation usually does not explain right-sided leg pain.
- A severe-looking finding may cause no pain if it doesn’t match your symptoms.
- A mild-looking finding can matter if it lines up with your pain pattern and exam.
What I look for isn’t just whether something looks abnormal, but whether it matches the side and path of the patient’s leg symptoms.
How Doctors Diagnose Sciatica
Diagnosis puts several pieces together; no single one is perfect.
History
Your history is the story of your symptoms — where the pain starts and travels, whether it goes below the knee, where you feel numbness, tingling, or weakness, how far you can walk, what positions help or worsen it, how long it’s lasted, and what you’ve already tried. Often the story gives the first strong clue.
Physical Exam
A physical exam checks whether a nerve is affected. It may include strength, reflex, and sensation testing (feeling in the skin), a straight leg raise, nerve tension tests, watching your walk, and hip or sacroiliac joint screening when needed. A straight leg raise test lifts the leg while you lie down to see if it reproduces nerve-type leg pain.
MRI
MRI shows anatomy but doesn’t automatically prove the source of pain. Doctors look for compression (pressure) or inflammation (swelling or irritation) near a nerve that matches your symptoms. Reports describe findings with terms like disc protrusion, disc extrusion, foraminal or lateral recess stenosis, nerve root impingement, and canal stenosis — each defined in the MRI-report section below. What matters is whether they match the side, level, and pattern of your symptoms.
X-rays, CT, and EMG/Nerve Tests
Other tests help in certain cases. X-rays show bone alignment — arthritis, spondylolisthesis, scoliosis, and instability (abnormal motion between spine bones). A CT scan (computed tomography) uses X-rays for more bone detail, useful when MRI is limited or bone anatomy needs a closer look. EMG/NCS (electromyography and nerve conduction studies) are nerve tests that help when the diagnosis is unclear or symptoms may come from nerves outside the spine.
Sciatica Treatment: The Usual Stepwise Path
Most sciatica treatment is stepwise, unless there are red flags or worsening nerve problems. In my practice, the choice between time, therapy, injection, and surgery depends heavily on pain severity, the presence of weakness, and whether the MRI and symptoms line up.
Activity Modification and Time
Many episodes improve over weeks. That doesn’t mean the pain is “in your head” — nerve pain can be very real and severe — but inflammation around a nerve can settle with time. Prolonged bed rest usually doesn’t help; gentle movement is often encouraged as long as symptoms don’t worsen significantly. It helps to avoid positions that clearly flare the leg pain, and the right approach depends on the cause and your tolerance.
Medications
Medication choice depends on your medical history and risk factors. Common categories include anti-inflammatory medicines (when medically safe), acetaminophen, nerve pain medicines in selected cases, and short courses of other medicines based on clinician judgment. This article gives no dosing instructions — medication safety depends on kidney function, stomach bleeding risk, blood thinners, liver disease, heart history, and other factors.
Physical Therapy
Physical therapy (PT) is guided exercise and movement treatment. It may focus on mobility, core and hip strength, nerve mobility, posture, walking tolerance, and graded return to activity. Disc and stenosis patterns need different strategies — some disc symptoms flare with bending, some stenosis symptoms with standing and walking — so good therapy is matched to the cause and what your body can tolerate.
Epidural Steroid Injections
An epidural steroid injection delivers anti-inflammatory medicine near irritated spinal nerves, in the epidural space around the nerves inside the spine. It’s often used for leg-dominant nerve pain, and may be considered when symptoms continue despite nonoperative care or when pain is blocking progress with therapy. Injections reduce inflammation but don’t fix every structural problem, and relief varies — some people get strong relief, some short-term, some little benefit.
Planned future topic: ESI vs PT for sciatica
Surgery
Surgery may be considered when:
- Severe leg pain doesn’t improve with nonoperative treatment
- Leg pain keeps quality of life very limited
- Weakness is getting worse
- MRI findings clearly match the symptoms
- There is a specific problem surgery can address
Common operations include microdiscectomy (removing the part of a herniated disc pressing on a nerve) and decompression (creating more room around crowded nerves). The right operation depends on the cause — disc herniation, stenosis, foraminal stenosis, and spondylolisthesis may need different plans. Surgery is neither always needed nor always avoidable.
When Sciatica Is an Emergency
Most sciatica is not an emergency. But seek urgent or emergency care now if it comes with:
- New loss of bladder or bowel control
- Numbness in the groin or saddle area
- Rapidly worsening leg weakness
- New foot drop
- Fever, chills, or concern for infection
- History of cancer with new severe spine pain
- Major trauma
- Severe, unrelenting pain with systemic illness
Foot drop is trouble lifting the front of the foot while walking. Saddle numbness is numbness in the areas that would touch a saddle — the groin, inner thighs, and buttocks. These can signal serious nerve compression or other urgent disease. This article can’t determine whether your symptoms are urgent; if you have new bladder or bowel problems, saddle numbness, or rapidly worsening weakness, don’t wait for an online review.
Learn more: Cauda Equina Syndrome: The Spine Emergency Patients Need to Recognize
How to Read a Sciatica MRI Report Without Panicking
MRI reports are written for medical teams and often use alarming words. The words matter, but context matters more.
Words That Sound Scary but Need Context
- Degenerative disc disease: age-related disc wear. Common, and doesn’t always cause pain.
- Disc bulge: the disc extends beyond its usual border in a broad way. Common, including in people without symptoms.
- Disc protrusion: a focused herniation that pushes out but keeps a broad connection to the disc.
- Disc extrusion: a herniation where the pushed-out material has traveled farther through the outer layer with a narrower connection.
- Nerve root contact: a disc or bone change touches a nerve root, which doesn’t always mean it’s the pain source.
- Nerve root impingement or compression: contact or pressure on a nerve root; matters most when it matches your symptoms and exam.
- Foraminal narrowing (foraminal stenosis): the side exit tunnel for the nerve is smaller than usual.
- Lateral recess stenosis: narrowing in the side part of the spinal canal where nerve roots travel.
- Canal stenosis: narrowing of the main spinal canal; stenosis can also involve the lateral recess or foramen.
Learn more:
The Three Questions That Matter Most
When I review a sciatica MRI, I focus on three things:
- Is there a finding on the same side as the symptoms?
- Is it at a level that matches the pain or numbness pattern?
- Is there nerve compression or inflammation that fits the severity of symptoms?
These separate “an MRI finding” from “the likely pain generator” — the structure most likely causing the pain.
Why “Abnormal” Does Not Always Mean “Dangerous”
Many people have disc bulges, arthritis, or degenerative changes on MRI without pain. A report can read as “bad” yet not explain your symptoms — the clinical picture matters more than any single phrase in it.
After Treatment: How to Know If the Plan Makes Sense
A plan makes sense when your symptoms, exam, and imaging point to the same nerve. When they don’t line up — say, left-sided MRI findings but right-sided leg pain — or when recommendations conflict, it’s worth separating what the MRI shows, what symptoms it could explain, and what next step is reasonable before committing.
Not sure whether your MRI explains your sciatica?
Get a written MRI/case review from a board-certified spine surgeon. SpineClarity helps translate your MRI report into plain language and explains what next-step category may fit your situation — such as continued conservative care, injection discussion, surgical consultation, or urgent in-person evaluation when appropriate.SpineClarity is not emergency care and does not replace an in-person physician relationship.
Key Takeaways
- Sciatica is nerve-type leg pain, not a single diagnosis.
- The most common causes are disc herniation and spinal stenosis.
- MRI findings matter most when they match the side, level, and pattern of symptoms.
- Many cases improve without surgery; some need injections or surgery.
- Bladder or bowel changes, saddle numbness, or worsening weakness require urgent care.
Frequently Asked Questions
Can sciatica go away on its own?
Often, yes — many cases improve over weeks as nerve inflammation settles. But not always. Worsening weakness, severe lasting pain, or red flags can change the plan.
Does sciatica always show up on MRI?
No. Sometimes symptoms come from inflammation, small nerve irritation, or a non-spine cause, and findings can be hard to interpret without an exam and symptom map.
Is physical therapy or an epidural steroid injection better for sciatica?
It depends on the cause, pain severity, duration, and whether pain is limiting movement. They aren’t always competing choices — therapy and injection are sometimes used at different points in the same treatment path.
References
Ropper AH, Zafonte RD. Sciatica. New England Journal of Medicine. 2015;372(13):1240-1248. doi:10.1056/NEJMra1410151
Koes BW, van Tulder MW, Peul WC. Diagnosis and treatment of sciatica. BMJ. 2007;334(7607):1313-1317. doi:10.1136/bmj.39223.428495.BE
Kreiner DS, Hwang SW, Easa JE, et al. An evidence-based clinical guideline for the diagnosis and treatment of lumbar disc herniation with radiculopathy. Spine Journal. 2014;14(1):180-191. doi:10.1016/j.spinee.2013.08.003
Kreiner DS, Shaffer WO, Baisden JL, et al. An evidence-based clinical guideline for the diagnosis and treatment of degenerative lumbar spinal stenosis. Spine Journal. 2013;13(7):734-743. doi:10.1016/j.spinee.2012.11.059
Katz JN, Harris MB. Lumbar spinal stenosis. New England Journal of Medicine. 2008;358(8):818-825. doi:10.1056/NEJMcp0708097
Patel ND, Broderick DF, Burns J, et al. ACR Appropriateness Criteria® Low Back Pain: 2021 Update. Journal of the American College of Radiology. 2021;18(11S):S361-S379. doi:10.1016/j.jacr.2021.08.002