We performed a systematic review of the scientific literature to date on the on the natural history of lytic pars defects and lytic spondylolisthesis in different communities, especially which radiological features predict the development of spondylolisthesis in patients with lytic pars defects.
We identified 21 studies in the literature which proposed a total of 10 risk factors across three imaging modalities (X-ray, Computed Tomography and Magnetic Resonance Imaging). The risk factors were: Disc degeneration, a narrow transverse process, disturbed spino-pelvic alignment, high lumbar lordosis, coronally oriented facets above the level of the defect, facet joint tropism at the level of the defect, multifidus atrophy, lateral extensor muscle hypertrophy, thickened mucosal fat, and thickened subcutaneous fat.
We review the strength of the evidence for each risk factor, the practicalities/impracticalities of incorporating each into clinical practice and deficits and opportunities in the literature as a whole.
We found no single radiological feature that can accurately predict which patients with pars defects will develop spondylolisthesis and which will not.
Many radiological features were associated with development of isthmic spondylolisthesis, however most of these have been identified by cross sectional comparison of patients with isthmic spondylolisthesis to control groups either without pars defects or with pars defects but no spondylolisthesis.
The lack of longitudinal data makes it difficult to separate causes and predictors of spondylolisthesis from effects of spondylolisthesis.
Certain radiological features allow a surgeon to infer that some particular patients presenting with pars defects are at higher risk of progression, but no tool unifying the various disparate predictors exists to allow him or her to quantify this precisely.