To the Editor.—
Dr Chintapalli1 reports a single example of a spectrum of disorders of the spinal canal that can create both progressive myelopathy, as well as progressive radiculopathy. It calls attention to the biconvex2 "trefoil" narrowing of the spinal canal space as one of the mechanisms of acquired spinal stenosis. Figure 4 of Dr Chintapalli's report1 demonstrates a mild degree of such osteophytic hypertrophy with mild trefoil alteration of the spinal canal space. Others have demonstrated that such spinal canal stenoses can occur at thoracic, as well as cervical and lumbar levels.2,3 Verbiest3 points out that hypertrophy of the facets is an important additional cause of this trefoil alteration in spinal canal space.Furthermore as Verbiest3 has demonstrated, triangular excrescences near the facets may not only be calcified ligamentum flavum but actual excrescences of the facet itself. He also discusses calcification of ligamentum
Olson WL. Progressive Myelopathy. JAMA. 1985;254(19):2740–2741. doi:10.1001/jama.1985.03360190046019
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