Usefulness of Posner's definition of spinal instability for selection of surgical treatment for lumbar spinal stenosis.

The aim of this study was to determine the usefulness of Posner's definition of spinal instability for selection of surgical therapy for lumbar spinal stenosis. Sixty patients with lumbar spinal stenosis were studied. Thirty-three patients were found to have instability, as defined using Posner's method. Nineteen of the 33 patients with instability underwent decompression and instrumented fusion. The 14 remaining patients with instability underwent decompression alone. Twenty-seven patients without instability were treated by decompression alone. Patients treated by decompression and fusion obtained the best results. Good results also could be obtained by decompression alone only if patients did not have instability. However, patients treated by decompression alone in the presence of instability had the worst results. The Posner's definition of instability proved useful for selecting patients with instability for fusion treatment.