Sciatica vs. SI Joint Pain: How to Tell the Difference Without MRI - A physiotherapist’s clear guide

Folarin Babatunde PT PhD
Dec 3, 2025
6 min read

Cogent Rehab Blog

Folarin Babatunde PT PhD MScSEM MScPT BScPT

December 3, 2025

Introduction

When you feel pain in your lower back, buttock, or leg, two of the most common causes are:

Sciatica – irritation or compression of the sciatic nerve
Sacroiliac (SI) joint pain – irritation or dysfunction of the joint where your spine meets your pelvis

They can feel similar, but they’re not the same problem, and the treatment approach is different. The good news: in most cases, a skilled physiotherapist can distinguish between them without an MRI, using a detailed history and movement-based assessment.

If you’re dealing with ongoing back or leg pain, you can learn more about our approach on our Back Pain Physiotherapy in Burlington page.

What Is Sciatica?

Sciatica refers to pain caused by irritation or compression of the sciatic nerve or its roots in the lower spine (usually L4–S1). Common contributors include disc herniation, spinal stenosis, or inflammation around the nerve.

Illustration of the sciatic nerve running from the lower back through the buttock and down the leg, highlighting sciatica pain pattern — Sciatic Nerve

Typical clinical features:

Pain that starts in the low back or buttock and runs down the back of the leg, often below the knee
Described as burning, sharp, or “electric shock–like” pain
Often accompanied by numbness, tingling, or weakness in the leg or foot
Frequently worse with prolonged sitting, bending, coughing, or sneezing

Studies show that nerve-root irritation produces dermatomal patterns — meaning symptoms follow predictable nerve paths. You can read more about how we treat nerve-related back and leg pain here:

Back Pain & Sciatica – Cogent Rehab Burlington

What Is SI Joint Pain?

The sacroiliac (SI) joints connect the sacrum (base of the spine) to the pelvic bones on either side. SI joint pain arises when this joint and its supporting ligaments become irritated, stiff, or unstable.

Typical clinical features:

One-sided pain in the lower back or buttock, near the “dimple” at the back of the pelvis
Pain that often stays above the knee, though it may refer into the posterior thigh or groin
Worsens with transitional or single-leg tasks such as:
- Standing up from sitting
- Climbing stairs or walking uphill
- Rolling or turning in bed

Research shows that SI joint dysfunction often presents as non-radiating buttock pain, worsened by asymmetric loading.

If your pain feels more “pelvic,” hip or groin related, our Hip, Thigh & Groin Pain page explains how we assess and treat these regions in more detail.

Sciatica vs. SI Joint Pain – Key Differences

Physiotherapist Comparison Table

Use this as an educational guide, not a self-diagnosis tool. Your pattern may not fit perfectly into one column, especially if more than one structure is irritated.

Feature	Sciatica (Lumbar Radiculopathy)	SI Joint–Driven Pain
Primary pain area	Starts in low back or buttock, runs down the back of the leg.	Deep ache or sharp pain around the back of the pelvis/buttock on one side.
Radiation pattern	Commonly travels below the knee into calf or foot along a nerve path.	Usually stays above or around the knee; may refer to posterior thigh or groin but rarely below the knee.
Pain quality	Burning, sharp, electric, shooting; may feel like a “jolt.”	Dull ache with episodes of sharp or stabbing pain deep in the buttock or pelvis.
Neurological signs (numbness, tingling, weakness)	Common: sensory changes and weakness in a dermatomal distribution (e.g., L5, S1).	Usually absent. If numbness or weakness is present, another diagnosis (e.g., radiculopathy) should be considered.
Aggravating positions	Often worse with sitting, bending, coughing, sneezing, or straining.	Often worse with sit-to-stand, prolonged standing/walking, stair climbing, single-leg loading, rolling in bed.
Typical movement pattern	Flexion-sensitive: slouching, bending, or lifting may flare leg pain; walking sometimes eases symptoms.	Load-transfer sensitive: difficulty with asymmetrical tasks (standing on one leg, walking uneven ground, stairs, turning in bed).
Key clinical tests	Straight Leg Raise (SLR) and Slump test tend to reproduce leg symptoms below the knee.	Cluster of SI provocation tests (distraction, compression, thigh thrust, sacral thrust, FABER). 2–3+ positive tests strongly suggest SI joint involvement.
Imaging / MRI	MRI can show disc herniation or stenosis but is not routinely required unless red flags or severe/progressive deficits are present.	SI joint dysfunction is primarily a clinical diagnosis; imaging and diagnostic injections are used when the picture is unclear or persistent.

Note: These patterns combine current research with established diagnostic frameworks used in physiotherapy, orthopaedics and pain medicine. Not every case will fit perfectly into one column, and some people may have involvement from both the lumbar spine and SI joint.

For more complex or mixed presentations, a full assessment through our Orthopaedic Physiotherapy service in Burlington is often the best starting point.

Person with SI joint pain holding the back of their pelvis while climbing stairs

Do I Need an MRI to Know Which One It Is?

In most cases, no.

Current guidelines recommend against routine imaging for low back–related leg pain unless there are “red flag” signs such as:

Significant or progressive leg weakness
Changes in bladder or bowel control
History of major trauma, cancer, infection, or serious systemic illness
Severe, worsening pain not responding to appropriate care

A physiotherapist can usually determine whether your symptoms behave more like sciatica or SI joint pain through:

A detailed history of how the pain started and what makes it better/worse
Careful movement testing of your spine, hips, and pelvis
Neurological screening (strength, reflexes, sensation)
Specific nerve tension tests and SI provocation tests

If we’re concerned about red flags or atypical findings, we’ll communicate with your family doctor or specialist about whether imaging is needed.

For spinal-related pain patterns in the mid-back, you can also read our page on Thoracic Spine Pain in Burlington.

How Physiotherapy Helps Sciatica

For sciatica, physiotherapy at Cogent Rehab typically focuses on:

Reducing irritation of the nerve (manual therapy, graded traction techniques where appropriate)
Restoring healthy motion through the lumbar spine, hips, and pelvis
Nerve mobility exercises (“nerve glides”) to improve neural tolerance
Progressive core and hip strength to support the spine under load
Advice on sitting, lifting, sleep positions, and activity pacing
Gradual return to walking, daily tasks, and sport with a structured progression

You’ll find more detail on our approach to low back and nerve pain here:

Back Pain & Sciatica – Cogent Rehab Burlington

Patient receiving one-on-one back pain assessment at Cogent Rehab Burlington physiotherapy clinic.

How Physiotherapy Helps SI Joint Pain

When the SI joint is the main pain driver, treatment looks different:

Gentle mobilization or specific manual therapy to the SI joint and surrounding structures
Targeted strengthening of the gluteal muscles, deep core, and hip stabilizers to improve load transfer across the pelvis
Correcting contributing issues such as hip stiffness, lumbar movement patterns, or leg-length–related asymmetry
Coaching functional tasks (sit-to-stand, stairs, turning in bed, walking mechanics)
Guidance on braces, taping, and exercise progressions where needed

To read more about our approach to hip, pelvic and groin-related pain, visit:

Hip, Thigh & Groin Pain – Cogent Rehab Burlington

More complex cases may also benefit from our broader

Orthopaedic Physiotherapy service.

When to Seek Urgent Medical Help

Regardless of whether the source is nerve or joint, you should seek urgent medical attention (emergency room or same-day medical care) if you notice:

Loss of bladder or bowel control
Numbness in the saddle area (inner thighs, around the anus or genitals)
Sudden, significant leg weakness
Unexplained fever, weight loss, or feeling very unwell with back pain

These may indicate rare but serious conditions such as cauda equina syndrome or infection and require immediate medical assessment.

How We Approach This at Cogent Rehab Burlington

At Cogent Rehab Burlington, your assessment with a physiotherapist will typically include:

A thorough conversation about your pain, activities, and goals
Movement testing of your lumbar spine, hips, SI joints and thoracic spine where relevant
Neurological screening to check strength, sensation, and reflexes
Specific tests to stress the sciatic nerve and the SI joint
A clear explanation of our clinical impression (in plain language)
A personalized treatment plan, including hands-on care and a home program