Pelvic Instability: Hidden Cause of Back Pain

From Dr. Verg Chiropractic, Vancouver, WA and Clackamas, OR

Many people with low back, pelvic, or hip pain have been told it is a disc, arthritis, sciatica, or “just a strain.” They do the exercises, take the medication, maybe get an MRI that shows nothing dramatic, and the pain keeps coming back. In my experience, one of the most common reasons is that nobody checked whether the pelvis itself was stable.

Pelvic instability means the joints of the pelvis, the two sacroiliac (SI) joints in the back and the pubic bone joint in the front, move more than they should, or move unevenly from side to side. The ligaments that normally hold these joints together have been stretched or sprained. The muscles around them then turn on at the wrong time, trying to guard the joint, and the pain can show up in the low back, the buttock, the groin, the hip, or down the leg.

I treat the pelvis in almost every low back visit in our office, because I find it involved in nearly every one. This article explains what pelvic instability is, why it is so often missed, what a thorough evaluation should include, and how we treat it. Whether you live near our Vancouver, WA or Clackamas, OR offices or across the country, you can use it to judge whether your own pain has been properly evaluated.

Key Takeaways

Pelvic instability means the SI joints and pubic bone joint move too much, or unevenly, because their ligaments are stretched or sprained.
Research suggests the SI joint is the main source of pain in roughly 15% to 30% of people with low back pain, and many more have it alongside a disc problem.
It is missed because X-rays and MRI are still pictures of a problem of movement, and many exams never test the pelvis.
A joint that feels “stuck” may actually be unstable. Cracking it again and again gives short relief but does not hold.
Good care has two steps: restore balanced motion with gentle adjustments, then stabilize with a pelvic belt and targeted exercises.

What Pelvic Instability Is

Your pelvis is a ring. The sacrum, the triangular bone at the base of your spine, sits between the two pelvic bones and is held there by some of the strongest ligaments in the body. At the front, the two pelvic bones meet at the pubic bone joint (the pubic symphysis). Every step, lift, and twist sends force through this ring from your upper body to your legs.

These joints are supposed to move, but only a little. Serola Biomechanics, a company that has researched the sacroiliac joint since the late 1980s, describes the ligaments as the primary stabilizers of the joint and the SI joints as “two of the most important support centers of the body” (Serola FAQs). When those ligaments are sprained, the joint surfaces separate slightly more than normal, and the joint becomes hypermobile (Serola: Hypermobility & Hypomobility).

Two points from this research match what I see in our office every week:

A joint that feels stuck may actually be unstable. An overstretched SI joint can shift into a position where it locks. Researchers have called this a “fixated instability.” Adjusting it hard, again and again, without stabilizing it, does not fix the problem.
The front and back of the pelvis work as a unit. When one SI joint is too loose, the other is relatively fixed, and the pubic bone joint is often involved too (Serola: Symphysis Pubis Dysfunction). This is why I check the pubic bone on nearly every low back patient.

How common it is

The research Serola summarizes shows the SI joint alone is the main pain source in a large share of low back pain (Serola: Incidence):

Study	Patients	SI joint as the main source of low back pain
Bernard & Kirkaldy-Willis, 1987	1,293	22.5%
Schwarzer et al., 1995	chronic low back pain	13% to 30%
Cohen, 2005 (review)	low back pain	15% to 25%
Sembrano & Polly, 2009	368 new patients	up to 25% (hip or SI joint)

That means roughly one in four to one in five people with low back pain may have a pelvic problem as the main cause, before counting the many who have it alongside a disc or joint problem.

How it starts

In one study of 54 patients with injection-confirmed SI joint pain, 44% began with a traumatic event, 21% with cumulative strain, and 35% with no clear cause (Serola: Mechanisms of Injury). The common causes:

Car accidents: 13 of the 54 cases. Hard braking and side impacts twist the pelvis. See our page on chiropractic care after a car accident.
Falls onto the buttocks, missed steps, and hard landings on the feet.
Bending, lifting, and twisting at the same time, the combination the SI joint handles worst.
Pregnancy and childbirth: hormones soften the ligaments, and overstretched ligaments can tear.
Repetitive sports with rotation or one-leg landings, such as golf, bowling, skating, and running.
Contributing factors such as a leg-length difference, scoliosis, or gait problems.

Why Pelvic Instability Gets Missed

Pelvic instability is not rare. It is missed because of how most low back pain is evaluated.

Imaging rarely shows it. An X-ray or MRI is a still picture, and pelvic instability is a problem of movement. Serola notes that SI joint pain “is difficult to visualize with methods that are used to diagnose a herniated disc” and that dysfunction is “not necessarily evident in a single moment” (Serola). In one study Serola cites, 90% of women whose bone scans showed SI joint inflammation had normal X-rays. When the MRI shows a mild disc bulge, which many adults have, the disc gets the blame.

It often hides behind a disc problem. In the Bernard and Kirkaldy-Willis study, a third of the patients with SI joint problems also had a second condition. In our office this is the rule, not the exception. Many of my sciatica patients have both an irritated disc and an unstable pelvis, and they only get better when both are treated. As I tell patients, “We’re going to treat the pelvis and the disc separately.”

The pain shows up somewhere else. An unstable SI joint can refer pain to the buttock, the groin, the side of the hip, the front of the thigh, and down the leg. That looks like sciatica, a hip problem, or a groin strain. One study found that groin pain was the only symptom that set SI joint patients apart from other low back pain patients. If your main complaint is the hip, our article on hip pain causes and non-surgical chiropractic relief covers the other common causes.

The joint feels stuck, so it gets cracked, again and again. A loose joint can shift and lock. Patients tell me their hip feels “stuck” or that it “always cracks” and then feels better for a day. Adjusting that joint brings relief, but without stabilizing it, it slips again. As I explained to one patient after her first visit: “That tells us that we have pelvic instability. It can shift and get stuck again.” The real problem is not stiffness. It is that the joint is not held in place.

Nobody tested the pelvis. A quick exam of the low back checks bending, reflexes, and a straight-leg raise. Unless the examiner also tests the SI joints, the pubic bone, leg length, and the hips, pelvic instability simply never comes up.

Signs You May Have Pelvic Instability

These are the patterns I hear most often from patients who turn out to have an unstable pelvis:

Pain on one side of the low back, right over the dimple at the top of the buttock.
Buttock pain, or pain that travels into the groin, the side of the hip, the front of the thigh, or down the leg.
Pain or tenderness right at the pubic bone.
Leaning to one side when you sit, or not being able to sit straight.
Pain when you stand up from sitting, roll over in bed, climb stairs, or get in and out of the car.
A hip that feels “stuck,” cracks, feels better, then gets stuck again.
A hip or leg that “gives out” without warning.
Pain that flares after walking, running, or strength training, even when you are doing your exercises.
Low back pain that started after a car accident, a fall, lifting and twisting, or pregnancy and childbirth.
One leg that seems shorter than the other.

If several of these sound familiar and your treatment so far has focused only on the disc or the low back muscles, your pelvis may never have been properly examined.

What This Looks Like in Our Office

These are real patients from our clinic, described without identifying details.

“Sciatica” that was also an unstable pelvis

A young woman came in with constant right hip pain shooting down her leg to her foot, with numbness in the foot. It had started after she moved homes and lifted boxes. The pain sometimes made her cry. She could not sit straight and leaned to the left to keep weight off her right hip. She told me her hip felt “stuck.”

What I found: the right SI joint was restricted and inflamed, and the right pubic bone was tender. Testing the SI joint caused sharp pain that eased only when it cracked. Her straight-leg raise reproduced pain to the ankle at just 30 degrees. I also suspected an irritated disc at L4-L5.
Diagnosis: pelvic instability with right-sided sciatica and radiculopathy, plus a likely disc herniation.
Treatment: gentle drop-table adjustments of the right hip and pubic bone, a pelvic adjustment lying on her back, and gentle mid-back work. No forceful twisting. I asked her to wear a pelvic belt low around the pubic bone every night and whenever she sat, for two weeks straight, and planned decompression for the disc.
Improvement in the same visit: her straight-leg raise improved from 30 to 45 degrees after the pelvic adjustment. She could bend forward about 20 degrees farther, sit straight without leaning, and said her leg was “actually better.”

This is the case I use to explain the problem to patients. Her disc was real, but the pelvis was making it much worse. Treating only the disc would have missed half the problem.

Leg pain that shrank from three toes to one

A woman had pain radiating down her left leg into three toes. Her exam showed a muscle spasm pulling on the right side of the pelvis and a tight left iliopsoas, the deep hip flexor that attaches to the low back and pelvis. I treated her with pelvic decompression, which gently separates the pelvic bones to calm the spasm, plus hip work and a release of the iliopsoas.

Improvement: within about two weeks, the radiating pain had shrunk from three toes to one, and it appeared only briefly when she stood up from sitting. At one point in the visit she had no leg radiation at all. She continued with a home program of hip flexor and inner-thigh stretches, shallow lunges, squats, and band work.

Twelve years of low back pain

A woman in her sixties had lived with low back pain for 12 years and had been told she probably had arthritis in the SI joint. On her first visit I used only one technique, a gentle pelvic flexion drop-table adjustment. She then rose from a forward bend without holding on to anything, which she had not been able to do before.

From adjustment to stability

A man whose work kept him sitting for long hours had left-sided low back pain with compression in the lower lumbar joints. Over several weeks his bending restrictions went away and he no longer needed his back brace. Then a new pattern appeared: his left hip and SI joint ached after dumbbell workouts and walking. On that visit, testing reproduced pain at the back of the left SI joint and buttock, and I adjusted the hip on the drop table.

Then I taught him a prone half plank with a leg extension, to hold the pelvis steady. This is the stage many patients never reach. As I told him: “We just moved the joints, and that turns on the nerves so the muscles work better. Now you lock it in with the exercises.”

Pregnancy

Pregnancy hormones soften the pelvic ligaments, so pelvic instability is common late in pregnancy and after birth. A woman 32 weeks pregnant came in with sudden, sharp “lightning” pain in the pubic area. It was gone right after three gentle drop-table impulses to the pubic bone. Another patient at 36 weeks had shooting pain in her right SI joint and low back spasms that she first mistook for labor. For her, we added a pelvic belt between visits. Read more in chiropractic care during pregnancy.

After a car accident

Pelvic injuries after car accidents are among the most often missed. One patient, months after a crash, still had low back pain with bending, groin pain, and trouble sitting through long services. Her exam showed positive SI joint tests on both sides, a positive thigh thrust test on the left, and a left leg about 5 mm short. Her groin pain had improved with walking and stretching. We added a pelvic belt every couple of hours during the day and a referral to a pelvic floor therapist, because pelvic floor weakness was part of her picture.

At the other end of care, I look for the SI tests to turn negative. Another patient after a car accident reached her final exam about 85% recovered, with SI joint and Kemp’s tests negative on both sides and pain-free lumbar motion.

What a Thorough Evaluation Looks Like

You should know what a complete exam includes so you can judge whether your own injuries were properly evaluated. Don’t just trust credentials; know whether you received great care. When low back, pelvic, or hip pain keeps coming back, a complete evaluation should include:

A detailed history: how the pain started (a car accident, a fall, lifting and twisting, pregnancy, a move), where it travels, what makes it worse, and what has already been tried.
Symptoms rated on a 0 to 10 scale, including the low back, buttock, groin, hip, and leg, recorded so they can be compared later.
Daily activities: how long you can sit, stand, and walk, how much you can lift, whether you can bend, and whether pain wakes you or limits your work.
Posture and movement: standing posture, lumbar bending forward and backward measured in degrees, and a squat-and-rise test.
SI joint provocation tests on both sides, plus the thigh thrust test. Pain with these tests points to the SI joint.
The pubic bone: checked for tenderness and for one side sitting forward (pelvic torsion).
Leg length: checked lying down, because an unstable pelvis can make one leg measure shorter.
The hips: flexion and internal and external rotation on both sides, to separate a true hip problem from a pelvic one.
Disc and nerve tests: Kemp’s test, straight-leg raise with the angle recorded, reflexes, sensation, and strength, because a disc problem often comes with pelvic instability.
Hands-on palpation of the SI joints, sacrum, tailbone, iliopsoas, and the muscles and ligaments around the pelvis.
Testing before and after treatment. I re-check the straight-leg raise and bending right after a pelvic adjustment. A change in the same visit tells us the pelvis is part of the problem.
An imaging and lab plan when needed: X-rays or MRI when the history calls for it, and blood work (such as rheumatoid factor, ANA, and HLA-B27) when inflamed SI joints raise the question of inflammatory arthritis.
Written diagnoses and a written plan: visit frequency, home exercises, belt use, and activity limits.
Re-exams with measured improvement: percentage better, degrees of motion, and whether the SI tests have turned negative, with referral to a specialist (pelvic floor therapist, neurologist, orthopedist) when progress stalls.

A Brief Summary of the Treatments We Use

Treating pelvic instability takes two steps. First, restore balanced motion so no joint is stuck or overmoving. Then, teach the muscles to hold the pelvis steady. Skipping the second step is why so many people feel better for a day and then slip back. Our chiropractic back adjustments are the starting point for the first step.

Gentle pelvic adjustments

Pubic bone drop-table adjustment: you lie on your back and place your hands on your pubic bone. I press through your hands as the pelvic section of the table drops about half an inch. This is my most consistent technique for a forward-shifted pubic bone, a twisted pelvis, SI sprain, and pelvic pain in pregnancy.
Pelvic flexion drop-table adjustment: knees pulled to the chest while the table drops, often with you lifting your head as in a curl. Patients with pelvic instability and acute pain told me the drop alone hurt, and the head lift relieved it because it engages the abdominals and steadies the pelvis.
Osteopathic SI and hip work: slow, controlled stretches and pressure on the sacrum, SI joints, sacrotuberous ligament, and hips.
What I avoid: when the pelvis is unstable, I skip forceful twisting adjustments of the low back. More force on a loose joint is not the answer.

Waking up the muscles

Iliac crest pressure without a thrust: for pelvic instability I press repeatedly on the top of the pelvic bone. The muscles have been turning on at the wrong time, and this helps the brain become aware of the pelvis again.
Iliopsoas release and pelvic decompression: gentle traction to separate the pelvic bones slightly, plus a release of the deep hip flexor, to calm spasm.
Flexion-distraction and spinal decompression when a disc problem comes with the pelvic one. Learn more about traction therapy and spinal decompression.

A pelvic (SI) belt

A good SI belt acts like an outside ligament while the inside ligaments heal. Serola describes its belt as working “like an external ligament” with a firm layer that stops the joint at the end of its normal motion (Serola).

Where it goes: low, around the pubic bone, not on the waist. Serola places it between the front points of the pelvis and the top of the thigh bone.
When to wear it: usually at night and whenever you sit, or every couple of hours during the day, for the period I prescribe, often two weeks without missing a day.
Why not a wide back brace: as I explain to patients, the SI belt “tightens our bones… the body begins to shorten ligaments and we get more stability,” while a wide lumbar belt “has negative consequences if we wear it for a long time.”

Stabilization exercises

Once the joints move well, the exercises lock it in: abdominal bracing before every movement, dead bug (“if I lose this abdominal tension, the exercise ends”), prone half plank with leg extension, side plank, pelvic tilts, cat-camel with side bending, clamshells, and a single-leg bridge “to load one SI joint and help stabilize it.” Rehab is different from a workout: we want to feel tension, not pain.

Working with other specialists

When the picture calls for it, we coordinate with pelvic floor therapists, neurologists, and orthopedists, and order imaging or blood work.

Frequently Asked Questions About Pelvic Instability

What is pelvic instability?

Pelvic instability means the two sacroiliac joints and the pubic bone joint move more than they should, or move unevenly from side to side, because their supporting ligaments have been stretched or sprained. The surrounding muscles then guard the joint, and pain can appear in the low back, buttock, groin, hip, or leg.

Can pelvic instability cause sciatica-like leg pain?

Yes. An unstable SI joint can refer pain into the buttock, the side of the hip, the front of the thigh, and down the leg. Many sciatica patients have both an irritated disc and an unstable pelvis, and they improve only when both are treated.

Why doesn’t my MRI or X-ray show it?

Pelvic instability is a problem of movement, and an X-ray or MRI is a still picture. Diagnosis depends on hands-on testing: SI joint provocation tests, the thigh thrust test, a check of the pubic bone and leg length, and re-testing after a pelvic adjustment.

Is it safe to keep cracking a hip that feels stuck?

It may bring a day of relief, but if the joint is loose it will slip and lock again. Adjusting it hard without stabilizing it does not fix the problem. I use gentle, non-twisting adjustments, then a pelvic belt and stabilization exercises to hold the pelvis steady.

How long do I wear a pelvic belt?

I usually prescribe a pelvic (SI) belt worn low around the pubic bone at night and whenever sitting, or every couple of hours during the day, often for two weeks without missing a day. Placement and duration depend on your exam.

Get Your Pelvis Checked

If your low back, pelvic, or hip pain keeps returning, and no one has tested your SI joints, pubic bone, and hips, the pelvis may be the missing piece. In our office, pelvic evaluation is part of every low back exam, not an afterthought. Use the checklist above with any provider. If you are near Vancouver, WA or Clackamas, OR, we would be glad to see you. If your pain started in a crash, see our car accident chiropractor page, and if shoulder pain is part of your story, read our shoulder pain guide. More articles are in our Research Corner.

Dr. Verg Chiropractic offers a free consultation for new patients at both of our locations:

Vancouver, WA — 109 SE 101st Ave — (360) 203-6000
Portland / Clackamas, OR — 10001 SE Sunnyside Rd #120 — (503) 386-9819

Sources

This article is for general educational purposes and does not replace an individualized medical evaluation. Case examples describe individual patients without identifying details; results vary. Please consult Dr. Verg or another qualified healthcare provider about your condition.

Pelvic Instability: The Commonly Missed Cause of Low Back, Pelvic, and Hip Pain