Abstract
BackgroundA number of minimally invasive sacroiliac (SI) joint fusion solutions for placing implants exist, with reduced post-operative pain and improved outcomes compared to open procedures. The objective of this study was to compare two MIS SI joint fusion approaches that place implants directly across the joint by comparing the ilium and sacrum bone characteristics and SI joint separation along the implant trajectories.MethodsNine cadaveric specimens (n = 9) were CT scanned and the left and right ilium and sacrum were segmented. The bone density, bone volume fraction, and SI joint gap distance were calculated along lateral and posterolateral trajectories and compared using analysis of variance between the two orientations.ResultsIliac bone density, indicated by the mean Hounsfield Unit, was significantly greater for each lateral trajectory compared to posterolateral. The volume of cortical bone in the ilium was greater for the middle lateral trajectory compared to all others and for the top and bottom lateral trajectories compared to both posterolateral trajectories. Cortical density was greater in the ilium for all lateral trajectories compared to posterolateral. The bone fraction was significantly greater in all lateral trajectories compared to posterolateral in the ilium. No differences in cortical volume, cortical density, or cancellous density were found between trajectories in the sacrum. The ilium was significantly greater in density compared with the sacrum when compared irrespective of trajectory (p < 0.001). The posterolateral trajectories had a significantly larger SI joint gap than the lateral trajectories (p < 0.001).ConclusionUse of the lateral approach for minimally invasive SI fusion allows the implant to interact with bone across a significantly smaller joint space. This interaction with increased cortical bone volume and density may afford better fixation with a lower risk of pull-out or implant loosening when compared to the posterolateral approach.
Highlights
A number of minimally invasive sacroiliac (SI) joint fusion solutions for placing implants exist, with reduced post-operative pain and improved outcomes compared to open procedures
This study will compare the overall bone, cortical, and cancellous bone density, and bone fraction lying along the two most common MIS Sacroiliac joint (SIJ) fusion trajectories that place implants directly across the joint, the posterolateral and lateral approaches, by using a simulated surgical model
The posterolateral approach was developed because it was the more direct trajectory of the two and did not necessitate retracting through large quantities of soft tissue dissection, with implants placed starting near the PSIS, traversing the ilium, crossing the ligamentous portion of the SI joint, and into the sacral ala [15]. While these differences are apparent in the clinical literature, our goal was to ascertain the differences in the trajectories not based in their directness of approach or soft tissue characteristics, but the overall quality of the bone that was traversed in patients with conditions such as osteoporosis and low bone density
Summary
A number of minimally invasive sacroiliac (SI) joint fusion solutions for placing implants exist, with reduced post-operative pain and improved outcomes compared to open procedures. This study will compare the overall bone, cortical, and cancellous bone density, and bone fraction lying along the two most common MIS SIJ fusion trajectories that place implants directly across the joint, the posterolateral and lateral approaches, by using a simulated surgical model (other dorsal approaches that place implants within the joint were not considered in this analysis). This will be accomplished through the introduction of virtual cylindrical dowels across the joint and the analysis of the different qualities of bone in the lateral versus posterolateral trajectories
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