Radiology of Lumbar Instability

In an era of increasing use of spinal hardware whether for fusion or to preserve segmental motion, radiologic determination of spinal instability plays a prominent role in the treatment algorithm for practically all disorders affecting the spine. Although the presence of spinal instability does not always equate to symptoms directly related to the instability, spinal imaging in combination with clinical history and physical examination can provide valuable insights into the preoperative evaluation of patients, the selection of treatment options, and the subsequent postoperative follow-up. For instance, patients with confirmed instability are currently contraindicated for total disc replacements because of concerns with the long-term survival of the discs, while the presence of instability at the segment above a fusion or disc prosthesis is indicative of adjacent level disease. This article reviews the radiology of spinal instability in patients with degenerative disc disease. Instability secondary to other common causes such as trauma, congenital anomalies, deformity, inflammatory disorders, and prior surgery are outside the scope of this review.