1. 2022;25;E469-E479Transfixation of the Sacroiliac Joint: Biomechanical Stability of a Dual-Implant Minimally Invasive Procedure
   Animal Study
   Steven M. Falowski, MD, and Antonio Valdevit, PhD.

BACKGROUND: Despite minimally invasive techniques for sacroiliac joint fixation, clinical challenges remain. The investigators hypothesized the studied technique will transfix the sacroiliac joint to a level comparable to the intact sacroiliac joint.

OBJECTIVES: The study objective was to determine the dynamic stability of a square inter-joint implant using a triangular notch in opposing bone segments spanning the joint space.

STUDY DESIGN: Stability was assessed by measuring micromotion using contralaterally placed transducers spanning the sacroiliac joint of a specimen during cyclic loading.

SETTING: A porcine in-vitro model was equipped with micromotion transducers on the intact and surgically implanted sacroiliac joint. Cyclic loading was applied on the L4 vertebra and the recorded micromotion data at each sacroiliac joint was analyzed.

METHODS: Porcine specimens from L3 to the sacrum including the pelvic ring were used to biomechanically evaluate the implantation technique. A novel technique consisting of a square inter-joint implant was placed so as to create a triangular stabilization notch within adjacent boney components of the sacroiliac joint. Displacement transducers were placed across implanted and contralateral porcine sacroiliac joint. Specimens were subjected to compressive loading between -10N and -100N followed by bending/rotation between 0.4Nm and 4.0Nm. Tests were conducted at 0.5Hz for 200 cycles. For each loading mode, transducer deflections (or rotations) were averaged at five-cycle intervals. Student’s t-tests were used to compare fitted parameters between implanted and intact sacroiliac joint.

RESULTS: In compression, implanted SIJ displayed reduced deflection compared to intact sacroiliac joint (P < 0.0001). In bending/rotation, initial rotation for the intact sacroiliac joint was increased compared to implanted sacroiliac joint (P < 0.0001). The computed Half-Life parameter represents the number of cycles at which the initial rotation decreases by 50% and was found to be statistically reduced for implanted sacroiliac joint as compared to intact sacroiliac joint.

LIMITATIONS: The use of porcine specimens resulted in uniform and good quality bone purchase. Further study may be required to evaluate the technique in older patients where bone quality is reduced.

CONCLUSIONS: Compared to the intact sacroiliac joint, the implant and procedure in this study demonstrated decreased motion under cyclic compression. Under rotation, the implanted sacroiliac joint displayed increased initial stability that subsequently normalized to intact sacroiliac joint values.

KEY WORDS: Transfixation, Minimally invasive, Sacroiliac Joint, Micromotion, Biomechanics, Dynamic Loading, Stability, In-Vitro