The Basics of Spinal Instability

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:

X-ray

• 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)

MRI

• High-intensity zones in your discs

CT

• 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)

Spinal Ligaments

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.

Spinal Muscles

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.

Nervous System

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.