Spinal stability and spinal instability are terms tossed around a lot, especially in rehab clinics and personal training facilities. After a couple of Pilates classes, you may think that your lack of spinal stability is based on your pelvic position and/or how strong your core and back muscles are.
But that’s only part of the picture. Spinal stability can be related to one, two or three “sub-systems” that greatly influence your spine—all the time. These are:
the spinal column and its ligaments
your nervous system, which controls spinal movement
your muscles, which move the spine
When any one of these sub-systems becomes damaged—say from age-related degeneration, fractures, iatrogenic injury, or even spinal tumors—the other two sub-systems must compensate.
The resulting imbalance can lead to an unstable spine, which will likely have problems carrying its own weight, not to mention the weight of an external load you add by picking up children, taking the groceries in, etc.
Notice how spinal stability can be a consequence of any number of possibilities that may go wrong. This means that the way to treat it or manage it will most likely differ, depending on which sub-system is affected and what exactly is going on with it.
Getting a diagnosis for spinal stability is based on the observable signs (factors that can be measured or objectively determined) and symptoms (your subjective experience, which may include pain, other sensations and things you notice about the way your back is functioning).
Let’s take each sub-system in turn and understand how it keeps your back healthy and pain-free by contributing to spinal stability.
1/Spinal Column and Ligaments
Injury or damage to your spinal column is the most common cause of spinal instability according to Biely, et. al. in their article, "Clinical Instability of the Lumbar Spine: Diagnosis and Intervention."
The spinal column is a complex structure, which means there are a number of ways problems can develop in this subsystem. Consider:
The spinal column is a series of 33 interlocking bones with discs in between. The front part consists of cylindrical vertebral bodies with cushioning discs in between. In back (of most vertebrae) is a ring of bone. The inside of the ring is hollow, allowing the spinal cord—a key structure of your central nervous system—to pass.
On the top and bottom of the bony ring (on either side) are extended areas called facets. As a whole, facet joints help bring integrity to the spine and its movements.
Your spinal column sub-system may be altered—and therefore may be the source of instability—if any one of the following is evident from diagnostic tests:
One or more vertebrae has translated (i.e. moved parallel) relative to the bone above or below (spondylolisthesis.)
Excessive flexion or extension, often created by cervical disc disease, and which may result in kyphosis.
Bone spur on the front edge of a vertebral body (called a traction spur)
High-intensity zones in your discs
Gapping of more than 1mm at your facets joints while you’re twisting your spine
Moderate to severe degeneration (on MRI but correlated with a low-pressure discography test)
As far as ligaments are concerned, capsular ligaments which cover and support the facet joints can become lax. When they do, they introduce excessive movement—and, therefore, instability—in your spine.
Among the many possible causes of capsular ligament laxity are disc herniation, spondylosis, whiplash-related problems and more.
Muscles are the powerful engines that move your spine. Part of their job includes providing stiffness and stability, as well.
Spinal instability can be the result of weakening or damage to the muscles that support the spine, such as the multifidus or the transverse abdominal. Ultrasound may show a wasting (which is a sign of weakness) of deep spinal muscles, while electromyography (EMG) is often used to detect muscle change.
The third spinal subsystem that influences stability is the nervous system. The nervous system is responsible for receiving messages about the position of the spinal bones and column and for producing impulses to move. These impulses are relayed to the muscles, signaling them to contract. Muscle contraction powers the spinal movements and provides stability.
So, if your muscles are slow to contract or they do so in an abnormal pattern, you may have a disruption to this neural control sub-system. These two factors can be detected by an EMG test. These disruptions can cause changes in spinal movement patterns, which can be observed by a trained eye (or by a motion detector machine).
Abnormalities in the neural control sub-system can also be detected by a nerve conduction study (NCS). An NCS is often performed along with an EMG to detect associated muscle irritation or damage.
When it comes right down to it, you really can’t tease apart one spinal subsystem from the other, say Biely, et. al. Instead, clinical instability is really a multi-system dysfunction. They say that some patients develop coping mechanisms (such as developing new patterns of muscle use that take over the job of stabilizing) while others do not. The “non-copers,” as they Biely, et. al. call them are more likely to come up with signs and symptoms of spinal instability.