Radiographic Assessment of Lumbar Facet Distance Spacing and Spondylolysis

Abstract

In Brief Study Design. Spondylolytic defects at L5 are influenced by insufficient differential spacing between the inferior articular facets of L4 and superior facets of S1. These structures then impinge on the intervening L5 pars interarticularis during hyperlordosis, contributing to fracture and resorption of the pars. Objectives. Articular facet spacing was evaluated on clinical radiographs of normal and spondylolytic patients. Summary of Background Data. Spondylolysis ranges from a hairline fracture through the pars to a complete pseudarthrotic defect. Insufficient increase in the distance between articular facets from L4–L5 to L5–S1 has been associated with chronic lytic defects in a skeletal sample. Methods. Anteroposterior radiographs of 39 patients with L5–S1 spondylolysis were compared with radiographs from 42 normal individuals. Differences in transverse distances between lumbar articular facets and pedicles were compared using 2-tailed t tests. Results. Patients with spondylolysis exhibited a smaller increase in interfacet distance from the L3–L4 facet joints to the L5–S1 joints than do normal patients, even relative to vertebral size. Conclusions. Spondylolytic fractures at L5 are influenced by an inadequate increase in interfacet distances between adjacent vertebrae. Individuals lacking sufficient increase in lower lumbar transverse interfacet dimensions are at greater risk of developing and maintaining spondylolytic defects. Inadequate increase in mediolateral separation between articular facets from L4 to S1 is associated with chronic L5 spondylolysis in an osteologic collection. Using standard anteroposterior clinical radiographs, we demonstrate that lytic patients have less interfacet distance increase from the L4–L5 to L5–S1 facet joints than do normal individuals.