Introduction:: Sacroiliac joint (SIJ) fixation has historically been an open and relatively invasive procedure. With the advent of recent minimally invasive techniques, complications and morbidity have declined. However, there remain significant clinical challenges associated with this complex anatomic joint. with appropriate diagnosis as a clinical challenge Low back pain can be attributed to involvement of the hip, lumbosacral spine or the SIJ in some combination with the latter consider after other anatomic site have been dismissed. The current study addresses use and functionality of a novel intra-articular implant that stabilizes the SIJ by transfixing across the SI joint by engaging both the sacrum and ilium. Stabilization is achieved by imparting a 3D toothed rectangular implant where the corners engage both the sacrum and ilium. Up to two devices can be placed perpendicular to each other establishing a convergence. The goal of the current study is to determine if such a minimally invasive surgical procedure can provide sufficient stability across the SIJ by employing a uniquely shaped implantation site consisting of triangular grooves in both the ilium and sacrum thus allowing the implant corners to lock into the triangular grooves. The investigators hypothesized that such a technique will stabilize the SIJ by engaging the bone surfaces within the triangular grooves thereby creating a compressive force across the SIJ and establish stability. It is further hypothesized that such a configuration will lead to initial stability, and result in comparable stability to the contralateral SIJ instrumented with a traditional screw fixation after cyclic loading.
Materials and Methods:: 7 specimens (4 males; 63-86, 3 females; 54-74) were denuded except for the sarco-pelvic restraining ligaments. The distal aspects of the pelvic wings and the L3 vertebra were independently embedded in resin thereby unconstraining motion of the pelvic wings. 3D motion sensors 1.8 mm in diameter were placed bi-laterally on either side of the SIJ to acquire motion data (Polhemus VIPER™ Polhemus, Colchester, VT) (Figure 1). In addition, customized Arc transducers were fabricated to measure the SIJ gap motion (Figure 2, Inset).1 The output voltage from these devices is linear with respect to the deformation across the radius which spanned the sacroiliac joint (Figure 2).Specimens were subjected to 6 continuous cycles of compressive loading from -75 N to -750 N through L3 at 1Hz with 3D motion data collected at 30 frames/s and Arc transducer data acquired at 40Hz/channel (Intact Condition)(Figure 3). Implantation of a single (worst case condition) 3D rectangular implant and a 6.5 mm cannulated screw were performed (bilateral) (Figure 4). Following implantation, the 6-cycle continuous loading test was repeated (Post-Implantation Condition). All specimens were then subjected to 20,000 cycles of fatigue loading at the prescribed loading levels. At 10,000 cycles, 3D motions and Arc transducer data was acquired (Mid-Fatigue Condition). Upon completion of fatigue loading the prescribed 6 cycles of testing was repeated (Post-Fatigue Condition).A 1-way ANOVA with Šídák's multiple comparisons test was used to determine statistical differences between the implants. 3D motion data was compared using the implanted state as the baseline.
Results, Conclusions, and Discussions:: All sevens specimens and implants survived the fatigue protocol. Device translational motion was examined for the 3D rectangular implant and a 6.5 mm cannulated screw under loading and revealed no statistically significant differences between the implanted, Mid-Fatigue and the Post-Fatigue conditions (Figure 4). Rotational motion between the 3D rectangular implant and a 6.5 mm cannulated screw revealed no statistically significant differences between the implanted, Mid-Fatigue and the Post-Fatigue conditions (P >0.117; Transverse Plane, P >0.497; Frontal Plane, P >0.058; Sagittal Plane). With respect to the sacroiliac joint gap measurements using the Arc transducers, both devices were comparable at each testing condition (P >0.236 for all).Both devices provided stability within the clinically acceptable range (Figure 5)1 The application of traditional mechanical loading to failure of a surgical construct does not represent a clinically viable scenario unless one considers resistance to traumatic loads. The current study investigated the response to cyclic loading of the SIJ in the transfixed and intact conditions. Common methods employ three-dimensional motion sensors or optics to ascertain SIJ motion. While commonplace, the resolution associated with these systems make their application challenging when applied to the SIJ where changes are often less than 1 mm. Using custom fabricated and calibrated transducers mounted directly across both sacroiliac joints, we were able to measure micromotion across the respective joints under cyclic loading resulting from device implantation. While both devices provided comparable performance, the ease of insertion and mitigation of trauma associated with the TransLoc device leads to a more clinically viable option.
Acknowledgements (Optional): : 1. Stallmeyer, M., Zoarski, G.H. (2004). Sacroiliac Joint Injection. In: Johnson, B.A., Staats, P.S., Wetzel, F.T., Mathis, J.M. (eds) Image-Guided Spine Interventions. Springer, New York, NY. https://doi.org/10.1007/0-387-21794-0_13.
References (Optional): : 1. Stallmeyer, M., Zoarski, G.H. (2004). Sacroiliac Joint Injection. In: Johnson, B.A., Staats, P.S., Wetzel, F.T., Mathis, J.M. (eds) Image-Guided Spine Interventions. Springer, New York, NY. https://doi.org/10.1007/0-387-21794-0_13.
