Lightning Podiums: Spinal Potpourri - 803B

Presented by: B. Cheng


D. Cook(1), C. Payne(1), M. Yeager(1), G. Schmidt(2), M. Oh(1), B. Cheng(1), D. Lindsey(3), S. Yerby(3)

(1) Allegheny Health Network, Neuroscience Institute, Pittsburgh, PA, United States
(2) Allegheny Health Network, Department of Orthopaedic Surgery, Pittsburgh, PA, United States
(3) SI-BONE, Inc., San Jose, CA, United States


Background: Surgical implant trajectories within the CT scan of human cadaveric pelvises of three lateral (L) and two posterolateral (PL) placements were analyzed to compare bone density and joint gap along them.

Methods: Nine human cadaveric specimens were CT scanned using a clinical CT scanner. The sacrum and ilia of each specimen were segmented. Cylindrical volumes approximating each trajectory were defined. The voxels of each CT scan lying within these volumes, and within the intersection of these volumes and each sacrum and ilium were identified. The voxel Hounsfield Units (HU) of these intersecting volumes were analyzed. The gap distance along each respective trajectory between the ilium and sacrum was calculated by finding the intersection of the trajectory and each of the bodies obtained from segmentation of the CT scan and defined as the joint gap distance. A two-way ANOVA on joint gap distance was conducted by (L vs. PL) with Bonferonni-correction post hoc analysis. A 2-Way MANOVA on Mean, Median, Cortical Volume, Bone Density, Cortical Density, Cancellous Density and Bone Fraction was conducted over Body and Orientation with Bonferroni-corrected post-hoc analysis.

Results: A significantly greater gap distance was found for the PL orientation compared to L (p< 0.001). The gap distance of PL1 was significantly greater than all other trajectories (p< 0.001), and that of PL2 was significantly greater than Top (p=0.003), Middle (p< 0.001), and Bottom (p=0.005) L trajectories. No significant differences were found in gap distance between any of the trajectories in the L Orientation. All bone quality measures except cancellous density were found to be significantly greater in the Ilium for the L trajectories compared to PL (p< 0.001). No significant differences were detected between orientations within the Sacrum. All seven measures of bone quality were significantly greater in the Ilium compared to the Sacrum when compared irrespective of orientation (p< 0.001).

Conclusions: The results of this study indicate greater bone density in the Ilium along the Lateral trajectory compared to the Posterolateral trajectory. The finding of greater density along this trajectory is driven not only by a greater volume of cortical bone in the lateral region, but also by a greater mean density of the cortical bone found there. These findings indicate a potential for superior fixation within the Lateral ilium compared to the Posterolateral. This study also demonstrates a greater gap between bony surfaces across the sacroiliac joint when approached posterolaterally. This may indicate greater obstacles to fusion across the fibrous tissues between the joint surfaces in that region compared to the lateral trajectory.

Figure 1 - Lateral and Posterolateral Trajectories

Figure 2 - Mean HU Between Lateral and Posterol