Spondylolisthesis without isthmus defect.

Abstract

With the development and widespread use of the moving grid in the 1920's, permitting satisfactory roentgenographic study of the lower spine, good understanding of congenital and acquired bone lesions in this area has become almost universal among roentgenologists, orthopedists, and industrial physicians interested in the low back. A great body of literature has developed concerning anomalies, residues of trauma, and degenerative disease of intervertebral disks and bone. We have observed in increasing frequency in older age groups, but in many who have presented low back problems in industry, a lesion which we believe has not had sufficient recognition. This belief is based on the sparse attention given to the lesion in the standard textbooks and in the literature (1, 2) and on discussion with our colleagues interested in diagnostic roentgenology and orthopedics. Spondylolisthesis, the term used to describe the extensive cases first observed by Kilian (3), may be translated literally as “falling of the vertebrae.” He dealt with extreme cases of forward dislocation of the fifth lumbar vertebral body over the sacrum, resulting in a large palpable mass in the pelvis, partially blocking the pelvic inlet in obstetrical cases. Most of the common cases now seen in x-ray study show only limited displacement, and spondylolisthesis has come to mean forward (or backward) slipping of one or more vertebral bodies on the segment below. Spondylolisthesis resulting from a defect in the isthmus or pars interarticularis has been recognized as a frequent and important structural lesion of the low spine. Spondylolisthesis also results, though less frequently, from anomalies of the articular processes and facets, fractures of the isthmus or articular processes, and destruction of these parts by inflammatory or malignant disease. In our experience, however, an increasing number of individuals have been seen with varying degrees of spondylolisthesis due to erosion of the facet joints in the lower spine by a degenerative arthritic process. The erosion of the cartilage and the subchondral bone in response to mechanical stress over the years is sufficient in some cases to permit forward displacement of certain lumbar bodies more than 1 cm. (Figs. 1 and 2). This process was apparently first described by Junghanns (2) in 1931 as “pseudospondylolisthesis.” We prefer to describe the lesion as a form of spondylolisthesis, recognizing that forward (or backward) slipping can result from a variety of causes. There are a few simple points of differentiation between spondylolisthesis resulting from isthmus defect and that due to degenerative arthritic erosion of the facet joints as demonstrated on lateral roentgenograms. When the lesions are clear cut and sharply defined, the interpretation is not difficult.