A Novel Posterior Implant System for Sacroiliac Joint Fusion: Preliminary Cadaveric and Clinical Results

Background Sacroiliac joint fusion is performed to stabilize and fuse the joint in patients with degenerative sacroiliitis and joint dysfunction. While several posterior techniques and implants exist as alternatives to lateral approaches, biomechanical and clinical performance data for these systems used as standalone remains limited. This article provides a preliminary cadaveric and clinical assessment of a novel posterior intra-articular sacroiliac fusion implant system. Methods A cadaveric biomechanical evaluation was conducted comparing the posterior implant to a posterolateral transiliac implant, evaluating each device's ability to reduce flexion/extension motion after initial fixation and fatigue loading when used as standalone fixation. Anatomical safety analysis was performed on each implant's post-fixation position, measuring minimum distances to critical SI landmarks on computed tomography (CT) scans. A retrospective clinical evaluation was also conducted, assessing early patient-reported outcomes for patients treated with the posterior device as standalone. Results Biomechanical stability in flexion/extension loading was greater with the posterior implant than the posterolateral implant, both post-fixation (31% motion reduction posterior; 4% increase posterolateral) and after fatigue loading (28% motion reduction posterior; 5% increase posterolateral). Strong effect sizes between implant groups were computed post-fixation (d = 1.92, p = 0.201) and post-fatigue (d = 1.63, p = 0.207), although these differences were not statistically significant with the limited sample size and inter-specimen variability. Compared to the posterolateral implants, the posterior implants were positioned approximately five times further from the sacral foramen (+13.6 mm, p = 0.020) and four times further from the anterior sacral border (+18.5 mm, p = 0.104). Clinical data on 10 patients treated with 13 standalone posterior implants found statistically significant improvements for mean Numerical Rating Scale (NRS) pain scores (4.7 points, 59% improvement, p = 0.014) and Oswestry Disability Index (ODI) scores (10 points, p = 0.029) at an average follow-up of 97 days. All domains of the Patient-Reported Outcomes Measurement Information System (PROMIS-29) assessment also improved (17% mean improvement), with most (4/7) domains showing statistically significant improvement. No device-related adverse events, removals, revisions, or follow-up procedures were reported. Conclusion These preliminary results suggest potential advantages in stability and safety for the novel posterior implant used as a standalone when compared to standalone posterolateral fusion. Early clinical data are promising, showing timely, statistically significant improvements in patient-reported outcomes. Additional biomechanical data and long-term prospective clinical data, including radiographic fusion evaluation, will be necessary to validate these results and further evaluate device performance.