Why SI Joint Instability Causes Chronic Low Back Pain

By Jacqueline Weisbein, D.O.
Double Board-Certified in Physical Medicine & Rehabilitation and Pain Medicine

Quick Insights:

SI joint instability occurs when the ligaments supporting your sacroiliac joint become loose or damaged. This allows excessive movement between your pelvis and spine. The instability disrupts normal load transfer during walking, standing, and bending. Many patients describe deep pelvic pain that worsens with movement. Imaging alone often misses this diagnosis. Persistent symptoms require specialized evaluation to identify the source.

Key Takeaways

• SI joint dysfunction accounts for 15-30% of chronic low back pain cases.
• Instability often develops after pregnancy, trauma, or repetitive stress injuries.
• Diagnostic blocks are commonly used to confirm SI joint pain, though single uncontrolled blocks carry a false-positive rate of approximately 20%, which is why controlled comparative blocks are preferred for definitive diagnosis.
• In some cases, conservative treatments may not provide sufficient relief, leading to consideration of interventional options.

Why It Matters:

Understanding the biomechanical cause behind your pain helps you stop guessing—and start pursuing accurate diagnosis and targeted treatment that addresses the real problem, not just the symptoms.

Introduction

As a double board-certified physician in Physical Medicine & Rehabilitation and Pain Medicine, I've helped many patients finally uncover the source of deep pelvic pain that was dismissed or misunderstood for years. Napa residents experiencing this type of chronic discomfort often feel frustrated by treatments that never address the underlying cause. To ensure patients receive expert and personalized care, I invite you to learn more about my credentials and approach as Dr. Jacqueline Weisbein, DO—board-certified pain management physician.

SI joint instability occurs when the ligaments supporting your sacroiliac joint become loose or damaged, allowing excessive movement between your pelvis and spine. Current consensus guidelines estimate that SI joint dysfunction accounts for 15 to 30% of chronic low back pain cases, yet it remains one of the most commonly missed diagnoses. This instability disrupts normal load transfer during walking, standing, and bending, creating that characteristic deep pelvic ache that worsens with movement.

For those exploring related spine or pelvic pain topics, it may help to read more about vertebrogenic low back pain and the specific factors that make diagnosis challenging.

At Napa Valley Orthopaedic Medical Group, I perform specialized diagnostic blocks and advanced interventional procedures to address SI joint pain when conservative treatments fail. Many patients come to me feeling frustrated after treatments that never addressed the root cause—and I want you to know that frustration is completely valid.

Understanding the biomechanics behind your pain is the first step toward accurate diagnosis and targeted relief. For patients interested in comparing conditions and care approaches, see our article on chronic vs. acute back pain and when to seek specialist care.

Understanding SI Joint Instability in Napa

Your sacroiliac joint connects your pelvis to your spine, transferring forces between your upper and lower body with every step you take. When the ligaments supporting this joint become loose or damaged, excessive movement occurs between these bones. This abnormal motion is what I call SI joint instability.

Biomechanical studies demonstrate that the SI joint allows for limited movement and primarily functions to transfer weight between the lower limbs and the axial skeleton. Instability in the SI joint, often due to ligamentous laxity or injury, can result in hypermobility, leading to increased movement beyond its normal range. The result is inflammation, muscle guarding, and that deep pelvic ache many patients describe.

In my Napa practice, I see patients who've been told their imaging looks "normal" despite debilitating pain. Standard X-rays and MRIs often miss SI joint instability because they capture static images. The problem is dynamic—it happens during movement. This is why specialized diagnostic testing becomes essential for accurate diagnosis.

How Pelvic Biomechanics Affect Your Lower Back

Your pelvis functions as the foundation for your entire spine, distributing weight from your upper body down through your legs. When your SI joint is stable, this load transfer happens smoothly and efficiently. When instability develops, your body compensates by recruiting surrounding muscles to provide the stability your ligaments can no longer offer.

Clinical research shows that SI joint dysfunction can lead to altered gait patterns and repetitive stress, potentially causing muscle discomfort in the lower back, buttocks, and hip regions. Your body essentially works overtime trying to stabilize an unstable joint. Over time, this chronic muscle tension becomes a secondary source of pain on top of the joint dysfunction itself. This is why some patients tell me they feel like their entire lower body is affected—it's not just the joint, it's the cascade of compensations that follow.

I've observed that Napa-area patients with SI joint instability often develop altered walking patterns without realizing it. You might favor one leg, shift your weight differently when standing, or avoid certain movements that trigger pain. These adaptations seem protective in the moment but actually perpetuate the problem by reinforcing abnormal movement patterns.

If you are struggling with ongoing back pain and are seeking the most effective therapy available, consider learning about chronic pain treatment options that can be tailored to your specific pelvic biomechanics and diagnosis.

Why Instability Creates Deep Pelvic Pain

The SI joint contains numerous nerve endings that detect position, movement, and tissue stress. When instability allows excessive motion, these nerves become irritated and send pain signals to your brain. Anatomical research on SI joint innervation confirms that the joint's abundant nerve supply, including nociceptive fibers, can generate significant pain when dysfunction creates abnormal mechanical loading and chronic irritation.

The pain typically feels deep in your pelvis, often on one side more than the other. Many patients describe it as a dull ache that sharpens with certain movements—standing from sitting, climbing stairs, or rolling over in bed. Unlike muscle pain that might ease with stretching, SI joint pain often persists because the underlying instability remains unaddressed.

In my experience, patients frequently report that their pain worsens as the day progresses. This pattern makes sense biomechanically—the more you move on an unstable joint, the more inflammation and muscle fatigue accumulate. Rest may provide temporary relief, but the pain returns once you resume normal activities.

If you are experiencing significant back pain localized near your pelvis or lower back, you may benefit from exploring minimally invasive back pain procedures that can specifically address both SI joint instability and related lumbar discomfort.

Common Causes of SI Joint Instability

Pregnancy is one of the most common causes I see in my practice. Research on postpartum pelvic dysfunction shows that hormones like relaxin and estrogen cause ligamentous laxity to facilitate delivery, and approximately 8–10% of women with pregnancy-related pelvic pain continue to experience symptoms for one to two years postpartum. These ligaments may not fully return to their pre-pregnancy state, potentially contributing to lasting SI joint instability. This explains why many mothers in Napa develop chronic low back pain months or years after delivery.

Trauma from falls, car accidents, or sports injuries can also damage the ligaments supporting your SI joint. Even repetitive stress from activities like running on uneven surfaces or heavy lifting with poor form can gradually stretch these ligaments beyond their normal capacity. Comprehensive reviews document that predisposing factors for SI joint pain include trauma, pregnancy, prior spine surgery, leg length discrepancy, and degenerative changes—often developing gradually rather than from a single event.

Degenerative changes in the spine can alter load distribution, potentially leading to increased stress and dysfunction in the SI joints.

How SI Joint Problems Are Diagnosed in Napa

Diagnosing SI joint instability requires a combination of clinical examination and specialized testing. I start by performing provocative maneuvers—specific movements and pressure tests that reproduce your typical pain pattern. Research on diagnostic accuracy shows that when three or more of six standard provocation tests are positive, sensitivity reaches 94% and specificity 78% for identifying SI joint pain.

The most definitive diagnostic tool is an image-guided SI joint block. I use fluoroscopy to precisely place numbing medication into your SI joint. In my practice, I use a 75% or greater pain reduction threshold to ensure the highest diagnostic confidence before recommending more definitive treatment. While guidelines commonly reference a 50% threshold, I prefer this more conservative standard because it helps me feel confident we've identified your true pain source. Controlled comparative blocks are considered the reference standard for confirming SI joint pain, giving us confidence to proceed with targeted treatment.

Clinical evidence confirms that identifying the correct pain generator is essential—when the SI joint is accurately diagnosed, targeted interventions can provide meaningful and sustained relief. Many patients I evaluate have undergone months or years of treatment directed at their lumbar spine when their SI joint was actually the problem. Once we identify the correct pain generator, we can offer interventional options specifically designed to address SI joint instability rather than continuing ineffective treatments.

For a deeper look at interventional spine therapies and what the recovery process entails, especially for conditions similar to SI joint problems, you might explore our detailed guide to Intracept procedure recovery.

A Patient's Perspective

As a physician who treats SI joint pain daily, I know that patient experiences reveal what clinical descriptions sometimes miss.

When patients describe their journey to diagnosis, they help others recognize patterns they might be living with. Krista shared her experience with our practice:

"Dr. Weisbein and her team are amazing at what they do. She and her medical assistant really listened to and got to the heart of my concerns quickly. Great first experience start to finish."

— Krista

This is one patient's experience; individual results may vary.

Getting to the heart of your concerns quickly matters when you've been searching for answers. Accurate diagnosis opens the door to treatment options specifically designed for your pain source.

Conclusion

SI joint instability disrupts the biomechanical foundation your body depends on for pain-free movement. When ligaments become loose or damaged, your pelvis can no longer transfer load efficiently between your spine and legs. This creates that deep, persistent ache that interferes with work, sleep, and the activities you love. As a double board-certified physician in Physical Medicine & Rehabilitation and Pain Medicine, I've helped many patients finally identify their SI joint as the true pain source after years of misdiagnosis.

Current consensus guidelines support a diagnostic approach that combines clinical examination with image-guided blocks to confirm SI joint dysfunction. When conservative treatments fail, interventional options like radiofrequency ablation can provide meaningful relief by targeting the nerves transmitting pain signals from your unstable joint.

I know how discouraging it can be to live with pain that no one has been able to explain. If you've been searching for answers, I want you to know there's a clear path forward.

We proudly serve Napa and nearby communities such as Sonoma, Vallejo, and surrounding areas. At my practice at Napa Valley Orthopaedic Medical Group, I focus on accurate diagnosis first, then personalized treatment plans that address your specific biomechanical problem. If you're ready to explore options beyond what hasn't worked, I'd be honored to help. You can schedule a consultation in Napa today to explore personalized pain management options.

Local medical facilities in the region include Providence Queen of the Valley Medical Center. The area is also served by Adventist Health St. Helena.

This article is for educational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition or treatment options. Never disregard professional medical advice or delay in seeking it because of something you have read in this article.

Frequently Asked Questions

How do I know if my low back pain is actually coming from my SI joint?

SI joint pain typically feels deep in your pelvis, often on one side more than the other. It worsens with activities like climbing stairs, standing from sitting, or rolling over in bed. Physical examination includes specific provocative tests that reproduce your pain pattern. The most definitive diagnosis comes from an image-guided SI joint block—in my practice, I look for a 75% or greater pain reduction after the injection to confirm your SI joint as the primary pain source with the highest confidence. Many patients I evaluate have undergone months of lumbar spine treatment when their SI joint was actually the problem.

Can SI joint instability heal on its own with rest and physical therapy?

Some cases of mild SI joint dysfunction respond to conservative care including physical therapy, activity modification, and anti-inflammatory medications. However, true ligamentous instability often requires more than strengthening exercises alone. Your body may compensate temporarily, but the underlying instability persists. When conservative treatments fail after several months, interventional options like radiofrequency ablation can provide sustained relief by targeting the nerves transmitting pain signals. The key is accurate diagnosis first, then matching treatment intensity to your specific biomechanical problem rather than continuing ineffective approaches.

What happens during an SI joint diagnostic block procedure?

I perform SI joint blocks in an outpatient setting using fluoroscopy (real-time X-ray guidance) to ensure precise needle placement. After numbing your skin, I guide a small needle directly into your SI joint and inject local anesthetic. The entire procedure takes about 10-15 minutes. You'll remain awake throughout and can describe any changes in your pain level immediately. If your typical pain decreases significantly within 30 minutes, we've confirmed your SI joint as the pain generator. Controlled comparative blocks are considered the reference standard for confirming SI joint pain, giving us confidence to proceed with targeted treatment options.

Where can I find SI joint instability treatment in Napa?

Dr. Jacqueline Weisbein at Napa Valley Orthopaedic Medical Group specializes in SI joint diagnosis and treatment using advanced interventional techniques. Located in Napa and serving Sonoma, Vallejo, and surrounding Wine Country communities, our practice combines thorough diagnostic evaluation with personalized treatment plans. Schedule your consultation today to take the first step toward lasting relief.