Radiological Evaluation of Lumbar Instability

Abstract

Lumbar instability of the lumbar spine is thought to be a possible mechanical mechanism underlying low back pain and is often an important factor in determining surgical indication for spinal fusion and decompression. Instability of the lumbar spine, however, remains a poorly understood subject. Clinical presentation is not specific, and the relationship between radiologic imaging of instability and its symptoms is controversial. Because of its simplicity, low expense, and pervasive availability, functional flexion-extension radiography is the most thoroughly studied and the most widely used method in the imaging diagnosis of lumbar intervertebral instability. In this article, we provide an overview of the current concepts of vertebral instability, focusing on degenerative lumbar intervertebral instability, and review the different imaging modalities most indicated in diagnosing vertebral instability. The spine is made up of segments, described as " locomotive segments, " consisting of two vertebrae and the interconnecting soft tissue. In normal conditions of daily life, the spine is able to meet essential functional requirements: strength, mobility, and stability. Spinal stability is defined as the ability for the vertebrae to maintain their relationship and limit their relative displacements during physiologic postures and loads. The requirement of stability is essential to the spinal column to prevent premature mechanical and biologic deterioration of its components. It is also fundamental to protect the spinal cord and nerve roots and to minimize energy expenditure. One important mechanical function of the lumbar spine is to support the upper body by transmitting compressive and shearing forces to the lower body during the performance of everyday activities. To enable the successful transmission of these forces, mechanical stability of the spinal system must be ensured. Stability of the lumbar spine as a whole is maintained by the cooperation of disks, joints, ligaments, and muscles. Degenerative processes in the disk and facet joints affect the stability of the motion segment. Although segmental instability is often used synonymously with degenerative spondylolisthesis, it is clear there are numerous other conditions that are potentially unstable (spinal acute trauma, surgery, spondylolysis, tumors, or infections).