Let the Assessment Be Your Guide: A Case of Dynamic Instability

Standing was agony. Walking was worse. But the moment she sat down or lay flat, the pain would ease completely. For a woman in her sixties, with no history of back problems, this pattern was the key to understanding what her MRI couldn’t show.

The Patient

She came to see me with a puzzle. A few months earlier, she’d developed sudden onset left leg pain—radiating down the side of her thigh and into her shin. There was no injury, no incident, no obvious trigger. It simply appeared.

Her medical team had arranged imaging and concluded she had nerve impingement on the left side of her lumbar spine. The diagnosis seemed straightforward enough. But something about her symptom pattern didn’t fit the typical picture.

The Positional Clues

When I asked what made her pain worse, the answer was immediate: standing and walking. Her walking tolerance was decreasing and would bring on significant leg pain. Standing still wasn’t much better.

And what provided relief? Sitting down. Lying flat. Sleep caused absolutely no pain whatsoever. These positions weren’t just tolerable—they were positions of complete respite.

This positional pattern was telling me something important. Pain that worsens with standing and extension, but disappears when lying down, points to a very specific type of problem: dynamic instability.

What Is Dynamic Instability?

To understand what was happening, you need to understand a condition called spondylolisthesis—where one vertebra slips forward over the one below it. In some cases, this slip is fixed; the vertebra has moved and stays in that position regardless of posture.

But in other cases, the slip is dynamic. It changes depending on position. In her case, when she stood up and arched her back slightly (extension), the slip increased. When she bent forward (flexion) or lay down, it reduced. This isn’t universal—dynamic spondylolisthesis can behave differently in different patients—but for her, extension was the problem.

Why does this matter? Because when the slip increases, it narrows the spaces where nerves exit the spine—the neural foramina. Stand up, extend slightly, and you’re literally closing down the exit tunnels for your nerves. The result: compression, irritation, and pain radiating down your leg.

Lie down, and those tunnels open back up. Pain disappears.

The Assessment

When it came to examining her, the clinical findings matched perfectly with my suspicions.

I put her through a series of neurodynamic tests—assessments that tension the sciatic nerve and its roots in different spinal positions. In flexion—rounding her lower back—I could pull on those nerves with no pain whatsoever. All flexion positions were comfortable.

The minute I put her into extension—arching the back slightly—and then tensioned the nerve, it reproduced all of her pain immediately.

And what made it even worse? Standing in extension. Just standing upright and arching her back slightly, without me even pulling on the nerve, increased her pain significantly.

The assessment was telling a clear story: extension closes something down; flexion opens it up. This is a common presentation with patients that have a suspected spondylolisthesis.

Going Back to the Imaging

Armed with what the assessment had revealed, I went back to her scans with fresh eyes.

Her MRI had been reported as showing “nerve impingement.” But when I looked carefully at the images, I couldn’t see any distinct neural compression on the left side. Yes, there were some mild disc bulges at L3-L4 and L4-L5. Yes, there were severely degenerated facet joints at L5-S1. But the nerve roots themselves? The L4, L5, and S1 nerve roots were all clearly visible with plenty of space around them.

MRI showing clear L5 nerve root with no obvious compression

As we know, a disc bulge can touch a nerve and cause absolutely no symptoms. Contact doesn’t equal compression.

But there was something else. Looking at the central images of her MRI, I could see a subtle difference—a small step between the back of the L5 vertebra and the back of S1. MRIs don’t show dynamic instability, however, she did have a set of dynamic X-rays and those images told a better story…

The Dynamic X-Rays

This is where her imaging told the full story. She’d had flexion-extension X-rays—dynamic images taken while standing, bending forward, and arching backward.

When she bent forward into flexion, there was approximately a 4-millimetre slip of L5 over S1.

When she stood up and extended slightly backward, that slip increased to approximately 6 millimetres.

Flexion X-ray showing L5-S1 with approximately 4mm slip

Extension X-ray showing L5-S1 with approximately 6mm slip - a 2mm increase demonstrating dynamic instability

A 2-millimetre difference might not sound like much, but in the confined spaces of the neural foramen, it’s significant. Upon standing and extending, the increased slip was closing down the space where her L5 nerve root exits—compressing it dynamically and causing the pain that radiated down the L5 distribution on the side of her leg and into her shin.

What the Reports Missed

Here’s what struck me: the flexion-extension X-rays were ordered—the right test for suspected dynamic instability. But the radiology report made no mention of any spondylolisthesis. None.

I don’t know why someone ordered these specific X-rays (I wasn’t the referring clinician) and then didn’t report the finding they were designed to detect. Perhaps it was oversight in a busy department. Perhaps there were other factors I’m not aware of. But it highlights something crucial: imaging is only as useful as the interpretation, and interpretation should be guided by clinical findings.

The Actual Diagnosis

The diagnosis wasn’t simply “nerve impingement.” It was nerve root irritation due to dynamic instability at L5-S1—a spondylolisthesis that increases on standing and extension, narrowing the neural foramen and compressing the exiting L5 nerve root.

Whether the underlying cause is a long-standing fracture in the pars (isthmic spondylolisthesis) or severe facet joint degeneration (degenerative spondylolisthesis) would require a CT scan to determine definitively. But for the purposes of management, the key insight was the dynamic nature of the problem.

The Path Forward: Conservative Management

She decided to pursue conservative management rather than surgery—a reasonable choice for many patients with this condition.

But conservative management for dynamic instability looks different from typical back pain rehabilitation. Because walking is a pain-generating activity for her, we had to be strategic.

Interval Walking

She has a limited tolerance for walking before her neural pain sets in. The approach isn’t to push through that pain—it’s to walk within her tolerance, stop or sit down before the pain escalates, recover, then walk again. Interval walking rather than continuous walking.

Over time, the goal is to gradually increase that tolerance. But you can only know if you’re progressing if you track it.

Why Tracking Matters

I always emphasise to patients the importance of tracking their tolerance and daily activity. Here’s why: when it comes to pain, humans have remarkably short memories. We don’t like to remember and imprint our pain experiences. We forget them quickly. And it works both ways—when you’re having a bad day, it’s easy to forget the good days you’ve had. Pain has a way of overwhelming perspective.

Without tracking, you won’t know on a day-to-day basis whether you’re actually progressing or not. Is your tolerance increasing? Are you walking further before pain sets in? You can’t answer those questions from memory alone.

Targeted Exercises

Alongside the interval walking, I prescribed a series of home-based exercises designed to increase both muscle strength and endurance. The hope is that building better muscular support around her spine can help increase her walking tolerance over time.

She had no desire to join a gym or do Pilates—she simply wanted to walk and do exercises at home. So that’s what we built her programme around. Meeting patients where they are is essential.

The Lesson: Let Assessment Guide Interpretation

This case reinforces something I’ve seen repeatedly over 30 years of practice: imaging alone doesn’t tell you what’s causing a patient’s pain. Dynamic problems—problems that only reveal themselves with movement or position change—can hide completely.

The assessment told me this was a dynamic, extension-sensitive problem before I’d even looked at her scans. When I went back to the imaging with that clinical picture in mind, the findings made sense. Without that guidance, you might look at her MRI and conclude there’s nothing significant—just some age-appropriate changes.

For Patients: What This Means for You

If your pain has a clear positional pattern—worse in certain positions, better in others—make sure your medical team knows. This information is crucial for interpretation.

If you’ve had imaging that doesn’t seem to explain your symptoms, it doesn’t necessarily mean the imaging is wrong or that your pain isn’t real. It might mean the problem is dynamic—something that changes with position and doesn’t show up when you’re lying still in a scanner.

Advocate for clinical assessment that correlates with your imaging. The scans are one piece of the puzzle. Your symptoms, your movement patterns, your responses to different positions—these are equally important pieces.

Key Takeaways

Positional symptoms are diagnostic clues. Pain that worsens with standing and walking but eases completely when sitting or lying down may suggest a dynamic problem—one that changes with spinal position.

Dynamic X-rays are crucial for dynamic problems. Standard MRIs are taken lying down with the spine unloaded. Flexion-extension X-rays capture what happens when you move, revealing instability that static imaging might miss.

Conservative management can work. Not every spondylolisthesis requires surgery. Interval walking, targeted exercises, and careful tracking can help manage symptoms and potentially increase tolerance over time.

Assessment should guide interpretation. Let the clinical findings direct how you read the imaging, not the other way around.

For more information on spondylolisthesis, dynamic instability, and managing pre and post-surgical care, join Vertera. Start your free trial now for comprehensive, expert-guided protocols.