Comparative Sacral Morphology in Spondylolisthesis Patients

Study design: Retrospective comparative case series.

Objectives: Evaluation of sacral morphology in spondylolisthesis patients compared with asymptomatic controls.

Summary of background data: Patients with spondylolisthesis are known to differ from asymptomatic controls in sagittal plane anatomy, but few studies examine the coronal and axial plane differences in these cohorts.

Methods: This is a retrospective evaluation of magnetic resonance imaging of the lumbosacral spine in 29 spondylolisthesis patients and an asymptomatic cohort (n = 154). Measurements of the linear distance and angular position of L5 and sacrum were performed in the sagittal, coronal, and axial planes. Receiver operating characteristic (ROC) curve analysis quantified these associations. High- and low-grade spondylolisthesis patients were compared with two-sample t-tests. All p-values are two-sided and considered significant when p < .05.

Results: Axial measurements showed the distance of the right to left anterior ala and the L5 body width did not differ between the cohorts. Sacroiliac (SI) joint angles in the spondylolisthesis cohort were closer to the true sagittal plane than in the controls 109° versus 121° (p < .001). In the sagittal plane, the linear measurement of the ratio of the midpoint anteroposterior width L5 to the sacral end plate was larger in the high-grade patients than the low-grade patients and controls. In addition, the kyphosis between S1-S2 and S2-S3 was larger in the spondylolisthesis cohort.

Conclusions: The SI joints in patients with spondylolisthesis were orientated closer to the sagittal plane than in the controls. An awareness of this positioning may be important in surgical implant insertion as well as rehabilitation of hip extensor weakness. The main anatomical differences found in this study were in the sagittal plane. Sacral end plate abnormalities were well visualized and consistent with radiographic findings in the literature.

Level of evidence: Level III, diagnostic.