An evaluation of sacroiliac joint stability with differing implant configurations in synthetic, cadaveric, and finite element models

Abstract

The sacroiliac joint (SIJ) bilaterally connects the sacrum and the ilium with an undulating articular surface and strong, stabilizing ligamentous structures that transfer load from the trunk to the lower extremities. The SIJ has been identified as the primary pain generator in 15-30% of patients presenting with low back pain and surgical fusion of the SIJ with instrumentation is frequently indicated to alleviate pain. The work presented in this thesis evaluated the biomechanical performance of a titanium triangular SIJ fusion system to characterize how implant quantity, pattern, and depth affect SIJ stability. First, mechanical testing was performed using a synthetic foam SIJ model to systematically evaluate multiple implant configurations before and after cyclic loading under physiological loads. Cadaveric biomechanical testing was then conducted to assess the SIJ stability with the use of two versus three implants. Finally, a basic SIJ finite element model was developed and used to further analyze the stability of different implant configurations. The results from these studies were used to identify implant placement recommendations to enhance the immediate post-operative stability of instrumented SIJ fusion procedures. The following recommendations are suggested for maximizing SIJ fusion stability: 1) use 3 implants whenever possible, 2) maximize implant spacing, 3) maximize implant depth, and 4) use non-collinear implant patterns.