Radiographic signs of implant loosening in sacroiliac joint fusion: an 11-year retrospective cohort study

INTRODUCTION: Sacroiliac (SI) joint dysfunction, an under-recognized cause of chronic low back pain, is predominantly prevalent in women. In selected patients it can be treated using minimally invasive fusion with stabilizing implants. While short-term outcomes of SI joint fusion (SIJF) are well documented, long-term effects and incidence of implant loosening remain relatively unknown. This study aims to determine both the incidence and potential risk factors of loosening after SIJF. METHOD: A retrospective longitudinal single-center study was conducted including all patients who underwent SIJF between 2011 and 2021. A subset with postoperative radiographs was analyzed for radiographic signs of implant loosening, indicated by radiolucency around the implant. Survival analyses were conducted to assess occurrence of loosening rates, and a risk factor analysis was performed. Additionally, specific locations of radiographic loosening signs were evaluated. RESULTS: A total of 297 interventions (211 patients, 187 females, mean age 47 years) were included. In all cases triangular titanium implants were used. Signs of radiographic implant loosening were observed in 39 SI joints. The one-year incidence of radiographic implant loosening was 2.0%, and the five-year incidence was 15.0%. The only factor associated with a higher risk of radiographic implant loosening was moderately impaired mobility (P < 0.001). Loosening signs were predominantly observed at the sacral side of the implant (67.2%). CONCLUSION: A one- and five-year incidence of respectively 2% and 15% of implant loosening was observed in SIJF. Moderately impaired mobility was significantly associated with loosening, but causality remains uncertain.