Understanding the Impact of L5 Spondylolysis on the Correlation between Pelvic Incidence and Sagittal Acetabular Orientation

Purpose: Surgeons are both interested in the relationship between spinopelvic parameters and acetabular orientation since concomitant diseases of the spine and hip are common. Spondylolysis of L5 is common in 4% to 8% of the population. L5 spondylolysis could potentially affect acetabular orientation since it is associated with alterations in the sacral and pelvic parameters. In our study, we aimed to assess the influence of L5 spondylolysis on acetabular orientation. Materials and Methods: In 23 patients with L5 spondylolysis and 46 control patients, we assessed the correlation between the pelvic parameters-pelvic incidence (PI), sacral anatomic orientation (SAO), and acetabular sagittal angle (ASA) using computed tomography analysis. The ASA is measured by the angle subtended by the line joining the anterior and posterior horns of the acetabulum in the midsagittal slice of the joint and the line through the anterior pelvic plane (APP). Results: Twenty-three patients with L5 spondylolysis were matched by age and sex (16 males; mean age, 46.1 years) to 46 control patients (32 males; mean age, 46.3 years). The PI and the ASA were significantly higher in those with spondylolysis, which indicates greater acetabular coverage relative to the APP. Linear regression analysis suggested a greater influence on ASA by the SAO than PI. Conclusion: Clinicians should be aware of the impact of elevated PI on the changes to the sagittal acetabular inclination and its association with spondylolysis. It should also be noted that spondylolysis alone does not appear to influence acetabular inclination in the sagittal plane.