A HISTOPATHOLOGICAL STUDY OF THE LIGAMENTUM FLAVUM/FACET JOINT COMPLEX IN PATIENTS WITH LUMBAR CANAL STENOSIS; NEW INSIGHTS INTO THE ANATOMY AND PATHOLOGY OF JUXTAFACET CYSTS.

Introduction: Thickened ligamentum flavum (LF) is a major contributor to the clinical syndrome of lumbar canal stenosis (LCS). The patho-mechanisms responsible for this phenomenon remain unclear. Cysts adjacent to facet joints (FJ) in the spine are regarded as rare entities that may uncommonly contribute to LCS. Inaccurate pathological interpretation and unawareness of a key anatomical feature has generated erratic terminology and confusion about their origin. Methods: Twenty-seven consecutive patients with radiologically confirmed central canal or lateral recess stenosis underwent lumbar laminectomy for neurogenic symptoms. Surgical specimens comprising en bloc excision of LF and medial inferior facet (to retain LF and FJ relationships) were examined microscopically following staining with haematoxylin-eosin and Miller’s elastic stain. Controls were facet/LF specimens from 89 cadaver lumbar spines. Results: Mean LF thickness was 8.9 mm (+/− 0.3 mm SEM) at the operated levels and 2.9 mm (+/− 0.3 mm) at the non-operated, adjacent levels (p Discussion: Para-facetal intraspinal cysts are common in degenerative lumbar spinal stenosis. DS is also a frequent finding but is statistically unrelated to cyst formation (Chi-square: p=0.187). We have found that debris from osteoarthritic facet joints enters a bursa-like cleft within the LF where it becomes incorporated into the wall where it excites a granulomatous reaction leading to blockage and synovial cyst formation. The existence of this channel has not been reported previously. We suggest that microscopic synovial cysts contribute significantly to the ligamentous thickening seen in LCS. We also present a novel classification of juxtafacet cysts based on our pathological findings.