The Association of Sacral Table Angle Measurements With Spondylolytic and Spondylolisthetic Defects at the Lumbosacral Articulation: A Radiographic Analysis.

Study Design: Retrospective radiographic study of 6 patients with L5 spondylolysis observed prospectively before the onset of lysis through adulthood. A radiographic analysis of 50 pediatric control subjects was compared with the study group.

Objective: To determine whether sacral table angle (STA) measurements bear etiologic association with the development of spondylolysis and/or subsequent spondylolisthesis.

Summary Of Background Data: Although radiographic parameters in association with spondylolysis and isthmic spondylolisthesis have been studied, no parameter has been shown to definitively have a role in development of this disease process. The STA is a recently described radiographic parameter useful in measuring anatomic changes across the lumbosacral articulation. This measurement's role as a predictor of pars lysis and subsequent slippage remains unknown.

Methods: The researchers examined the longitudinal plain radiographs of 6 patients observed from childhood, before the development of spondylolysis, through adulthood. Measurements of STA and percent slippage were performed. Fifty pediatric control subjects' radiographs were also examined with STA measurements. Statistical analysis was conducted on results.

Results: Mean STA of the study group before the development of spondylolysis was 95° ± 5.5°. Mean STA from the control group was 97.5° ± 4.3°. No statistical difference was found between groups (p > .05). No index patient had an abnormal STA before spondylolysis (less than 89°, defined as being outside 2 standard deviations from the control mean). Four of 6 index patients with spondylolysis developed spondylolisthesis. A negative correlation (r = .54) was seen for STA as a function of increasing percent slip when assessed longitudinally.

Conclusions: Abnormal STA measurement was not seen before the development of spondylolysis in this study population. Decreasing STAs were seen secondarily in patients with L5 spondylolisthetic progression. This finding points to anatomic change and secondary remodeling of the upper sacrum as a result of slippage.