“Your spine is unstable” is an alarming thing to be told, and in most cases it isn’t accurate. Here is what true instability is, and what it isn’t.
If you have struggled with chronic lower back pain and been told your spine is unstable, it is an unsettling phrase to hear. It is also, in my experience, one of the most frequently misused terms in spinal medicine. True instability is uncommon. The word gets applied to a great many situations where it does not belong.
How a normal spine holds together
Your spine is a stack of bones called vertebrae, held together by ligaments and cushioned by discs sitting between them. On an MRI scan of a normal spine you can see good alignment, with the natural backward curvature preserved.
Each segment is secured in two places:
- At the front, by the disc and the ligaments surrounding it
- At the back, by two joints called facets, again strapped together with ligaments
When you move, each segment should angulate only: a little rotation, some forward and backward bending, some sideways bending. What it should not do is slip forwards or backwards over the segment below.
What true instability means
By definition, true instability is excessive abnormal motion of a spinal segment. It matters because that motion can threaten the neurological structures, the nerves or the spinal cord, and because it causes mechanical pain.
It is usually the result of a failure of the spine’s structural integrity. A fracture is one obvious cause. It can also develop through excessive degenerative change in the facet joints, discs and ligaments, allowing one segment to slip gradually forwards or backwards over another.
Treating the patient, not the test result
Here is where the nuance lies. Finding abnormal alignment on a scan, where one bone sits slightly forward of another, is called a spondylolisthesis. It does not automatically mean the spine is dangerously unstable.
I have treated patients with exactly that finding whose back pain was minimal. Their problem was nerve pain from compression, causing symptoms radiating down the legs. What they needed was simply to have the nerves freed up. No instrumentation to stabilise the spine was required at all.
Similarly, where a scan shows the L5 vertebra slipped forward relative to the one below but the nerves in the canal are entirely free, there is no need to rush into surgery. Rather than stabilising the segment with metalwork, we can often build a rigid, powerful muscular brace around it through exercises taught by a good physiotherapist.
When surgery is warranted, and which operation
If conservative measures fail, there are effective procedures.
For a spondylolisthesis, my protocol depends on the level:
- At L5/S1, I usually approach from the front, with an anterior lumbar interbody fusion: a cage placed between the two bones, secured with screws, realigning and stabilising the segment.
- Above that level, I tend to fuse from the back, using a minimally invasive transforaminal interbody fusion (TLIF), with screws posteriorly and a cage in the disc space.
Both are very effective in the right patient.
A fracture with progressive deformity, where fragments threaten the nerves or spinal cord, is a clearer indication. An operation using screws and rods to realign the segment, reduce the fracture and decompress the nerves works well.
Where the word gets misused
Everything described above is genuinely uncommon. Yet I hear “instability” used constantly in situations that do not meet the definition.
A tear in the disc. Someone has long-standing back pain with flare-ups, a scan shows a disc tear, and the disc is labelled unstable on the grounds that it might herniate in time. In practice the lining usually scars over and heals. What we need to do is prevent a recurrence, which again comes back to building that muscular brace and, importantly, learning to trust your spine.
A herniated disc. I hear “the disc is unstable” here too. All it actually means is that the central fragment has poked out and may be pinching a nerve, causing sciatica. In the majority of cases this repairs itself well and needs no surgery. If surgery is needed, it is not a lumbar fusion. It is simply removing the offending fragment, a microdiscectomy.
“Core stability.” I confess this is a phrase I dislike. There is no such thing as an unstable core, only a strong or weak one, and weakness alone is not the reason you have back pain. That said, in the specific circumstances described above, strengthening the core to build a muscular brace around the spine can genuinely reduce abnormal mechanical motion, and with it the pain.
The key takeaway
Most of the time, instability is not the right word.
To confirm it, it must be demonstrated on a scan or X-ray. But even then, the finding alone does not mean something serious is happening, that your nerves are at risk, or that you need an operation. It is putting the imaging and the clinical picture together that matters.
I am a firm believer in clinical direction, with a surgeon taking responsibility for leading the physiotherapists and other professionals involved in your care, informed by both the images and the clinical picture. Non-surgical methods come first. Only if those fail, or if there is progressive deformity or a neurological problem, do we consider operating.
