AN ANALYSIS OF THE APPEARANCE ON SUPINE MRI OF OPEN AND CLOSED SUBLUXATIONS OF THE LUMBAR SPINE

Abstract

Objective: An anatomical study to describe the radiographic pattern of canal, foraminal and lateral recess stenosis in degenerative lumbar stenosis associated with open and closed subluxations of the lumbar spine.

Introduction: Degenerative lumbar scoliosis is a three-dimensional deformity frequently associated with facet joint subluxation. It is suggested that the causative mechanism of open subluxation is vertebral rotation, whereas closed subluxation is driven by erosion of the convex facet joint. Patients with degenerative lumbar scoliosis are predominantly symptomatic on standing. However, standing MRI scans are not currently feasible to investigate this dynamic problem, therefore an accurate interpretation of the standing and lateral radiographs is essential to effectively treat this condition. We have undertaken a study to compare standing radiographs with supine MRI to determine the pattern of nerve root entrapment with open and closed facet joint dislocations in DLS.

Methods: Plain radiographs and MRI scans of 35 consecutive patients with de novo degenerative lumbar scoliosis (average age 72 years) were evaluated. Radiographic measurements included the angle of the dislocation, degree of translation, position of osteophytes, vertebral rotation and the degree and location of any stenosis present on the axial MRI images.

Results: Open dislocations were associated with a pre-dominant contralateral lateral recess and/or foraminal stenosis in 74% of cases. Closed dislocations were associated with ipsilateral lateral recess and/or foraminal stenosis in 82% of cases. Both open and closed dislocations had a similar degree of vertebral rotation.

67% of open subluxations occurred at L3/4. In closed subluxations the most frequent level involved was LI/2 (53% of cases). Open dislocations are located closest to the apex of the curve, with closed dislocations being more peripheral. The curve was noted to rotate towards the apex.

Conclusion: Open and closed subluxations of the lumbar spine result in different, but predictable, patterns of stenosis. The findings are important in the diagnosis and planning of treatment in patients with lumbar spinal stenosis, when associated with degenerative scoliosis and lateral spondylolisthesis.