Spinal instability is the excess mobility of one vertebra on another. This can arise from an injury, or a longstanding degeneration of the joints and ligaments responsible for keeping the spine stable.
Spinal instability is suspected if imaging studies (such as an MRI, a CT, or plain X-rays) show disks or vertebral endplates with evidence of abnormal “wear and tear”, or a frank dislocation (spondylolisthesis) of one vertebra with respect to another.
Imaging studies suggesting instability. Left: Modic changes showing abnormal wear and tear on the disk. Right: A spondylolisthesis, or slippage of one vertebra over the other.
Spinal instability generally causes neck or back pain that worsens with motion. If it is severe enough to cause a disk herniation or stenosis (see above) it can cause arm or leg symptoms as well.
Though conservative nonoperative treatments such as steroidal and nonsteroidal anti-inflammatories, narcotic analgesics, epidural and facet injections, physical therapy, and braces may be helpful in managing symptoms, true instability eventually must be addressed surgically with a fusion procedure such as an ALIF, PLF, PLIF, TLIF, or XLIF along with minimally invasive lumbar instrumentation with screws and rods.