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 definitio n 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 me thod. Nineteen of the 33 patients with instability underwent decompression and instrumented fusion. The 14 remaining patients with instability underwe nt decompression alone. Twenty-seven patients without instability were trea ted by decompression alone. Patients treated by decompression and fusion ob tained the best results. Good results also could be obtained by decompressi on alone only if patients did not have instability. However, patients treat ed by decompression alone in the presence of instability bad the worst resu lts. The Posner's definition of instability proved useful for selecting pat ients with instability for fusion treatment.