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Spinal Instability

After a back injury, spinal instability is an important injury mechanism that might develop. The most common cause is disc injury. But any significant structural problem affecting the vertebrae, muscles, and ligaments may lead to instability.

What does spinal instability feel like?

Spinal instability pain is typically brief. Instantaneous. There one moment and gone the next. A catch when I roll over in bed. A stab in the back with bending. A twinge. Instability is sometimes associated with cracking, but is often silent. As a clinical diagnosis—determined primarily by the assessment rather than spinal imaging—patients often feel validated when they learn of this injury mechanism.

No one has asked me about pain with rolling over in bed, one patient told me. His enthusiasm was warranted—the classic symptom for instability is rolling over in bed. Performed casually, this movement involves the de-stabilizing combination of bending and twisting. Other patients with instability tell me that they don’t have pain with rolling over in bed but, it turns out, that’s because they are rolling over with good form, even rigidly, to avoid the catch.

Instability can cause back pain. Usually, the location of this pain is at the center of the back or off center. It tends to be very brief but very severe. Common descriptions are sharp and tight. If instability is the main injury mechanism, you might have long periods of relief between the aggravations. I observe that even when instability pain is intermittent, the severity and unpredictability of this symptom make it distressing. Instability can also cause sciatica pain the micromovement crushing down on the spinal nerves and its roots.

Variable symptoms are a clue that you might have instability. If you have pain that moves around, this may reflect the chaotic micromovement pinching different tissues. The pain might move from one part of your back to the other. Or it might cause sciatic symptoms in different parts of your leg—the big toe, then the outer part of the foot, then the sole—reflecting compression of different spinal nerves. Instability pain can even migrate pain from one leg to the other.

Subtypes of Injury

Micromovements

Micromovements are small and brief instability slippages. They are invisible to spinal imaging and diagnosed clinically. Micromovements provoke instantaneous symptoms most of the time. But greater levels of instability can cause you to throw out the back, leading to a longer pain crisis.

Isthmic Spondylolisthesis

Isthmic spondylolisthesis starts with a fracture of the neural arch called spondylolysis. This fracture de-stabilizes the spinal joint and predisposes it to dislocating with bend and shear forces. A dislocation occurring with this mechanism is called isthmic spondylolisthesis. This injury is graded by the extent of slippage dislocation of one vertebra relative to vertebra below it. As the spine dislocates, there is increased disc strain and narrowing of the passageways for the spinal nerves and its roots, which may cause sciatica. Most isthmic spondylolisthesis injuries occur at the L5-S1 level.

After spondylolisthesis occurs, the level of instability in the dislocated position predicts whether further slippage will take place. The key test to measure instability with isthmic spondylolisthesis is a series of x-rays called a dynamic series. In a dynamic series, the lumbar spine is visualized from a sideways sagittal view in three postures—flexed, extended, and neutral. The radiologist measures whether the extent of slippage increases between any two postures. A slippage of 4 millimeters or more indicates an unstable spondylolisthesis at high risk for progression to a higher grade of dislocation.

An unstable spondylolisthesis can be stabilized with fusion surgery.

Degenerative Spondylolisthesis

Degenerative spondylolisthesis is another type of dislocation injury. It starts with disc degeneration associated with a loss of disc height and stiffness. This structural change shifts compression load to the facet joints which, overburdened, will develop arthritis over time. The arthritic facet joints may lose their ability to hold the vertebrae in place and excessive bending and shear causes a permanent slippage and misalignment—the degenerative spondylolisthesis.

Degenerative spondylolisthesis will not occur with disc and facet degeneration alone. Rather, there needs to be a combination of degeneration and instability. Women, who are naturally more flexible due to their more supple ligaments, develop spondylolisthesis at five times the rates of men. Another important congenital factor is the structure of the facet joints, which determines their ability to resist slippage-inducing shear loads. The L4-L5 motion segment is most prone to shear—owing to its position along the lumbar lordotic curve—and is, not coincidentally, the site of most degenerative spondylolisthesis.

Unlike isthmic spondylolisthesis, degenerative spondylolisthesis rarely progresses beyond a grade 1 level of severity. Most of the time, the spine can heal by physiologic stabilization, a process of natural fusion attained by a combination of disc height narrowing and new bone formation that locks down the unstable disc. Instability can be assessed with a dynamic x-ray series. Non-operative treatment focuses on lumbar stabilization exercises and movement quality. Avoiding excessive bending is necessary for healing.

In 10-15% of cases, surgery is performed for degenerative spondylolisthesis. One category of surgery involves decompression only. Decompression relieves nerve pressure and is the surgery of choice when there is sciatica in conjunction with a stable motion segment. If there is marked instability, however, the surgical approach may include a decompression and fusion. For degenerative spondylolisthesis, the decision to undergo surgery, as well as the extent of the surgery, requires a high level of clinical judgement.

Pain-Triggers

Highly Variable and can be one or a combination of these forces:

 

    • Bending

    • Carrying heavy loads

    • Jolting activities

    • Twisting

    • Traction

Relieving and Therapeutic Factors

 

    • Posture

The best posture is a near-neutral posture which may, depending on the case, deviate mildly into flexion or extension.

 

    • Position of Respite: Variable

    • Stability with Bracing

       

        •  Abdominal bracing

        • Thoracic Bracing

    • Avoid your pain-triggers

    • Walk briskly. The momentum from walking quickly will engage your spinal extensor muscles and stabilize you.

    • Stability Exercises

Practicing stability exercises such as the McGill Big 3 will enhance your muscular endurance and stiffen your torso muscles. This protective stiffness after a Big 3 work out lasts for up to several hours. If you notice this immediate symptom reduction, perform your stabilization exercises twice a day to extend the therapeutic effect.

Healing Mechanism — Muscular Control and Conditioning, Disc Stabilization, and Osteophyte Formation

Instability resolves for most of our patients from a combination of spine hygiene and stabilization exercises. Spine hygiene involves avoiding the pain-triggers and a combination of good spine posture, sufficient stability through bracing, and moving well. The training effect of most benefit is muscular endurance, as it allows you to control your posture. The enhanced torso muscular stiffness is another benefit, which compensates for the spinal instability. The good news is the muscles, along with the ligaments and other connective tissues, are primarily responsible for your spine’s stability. With improved mechanical conditions, the disc will slowly stabilize over the following months. This adaptive process can extend for years, with the spine growing bone spurs around the disc—your spine’s way of naturally fusing for stability.

Select References

McGill, Stuart. Low back disorders: evidence-based prevention and rehabilitation. Human Kinetics, 2015.

Jim, Lysander. Specific Spine: A Doctor’s Guide to a Healthy Back. M.D. Muse Media, 2023.

Izzo, Roberto, et al. “Biomechanics of the spine. Part I: spinal stability.” European journal of radiology, 2013.

McGill, Stuart M. “Low back stability: from formal description to issues for performance and rehabilitation.” Exercise and sport sciences reviews, 2001.

Cholewicki, Jacek, and Stuart M. McGill. “Mechanical stability of the in vivo lumbar spine: implications for injury and chronic low back pain.” Clinical biomechanics, 1996.