Is osteoporosis an independent risk factor for sacral fracture after lumbosacral spinal fusion in adults? A retrospective cohort study.

Abstract

Sacral fracture is a rare complication following lumbosacral fusion in adults linked to postsurgical biomechanical changes. There are mixed research results suggesting that osteoporosis may or may not be a contributing factor. To determine if osteoporosis is an independent risk factor for sacral fracture after lumbosacral fusion. A propensity-matched retrospective cohort study that was preregistered on open science framework. After matching, patients (n=14,302; 82% female) who underwent lumbosacral fusion had a mean age of 64 years and were divided into the osteoporosis cohort (n=7,151) or the no osteoporosis cohort (n=7,151). The primary outcome measure was the risk ratio (RR) of sacral fracture through 2 years after lumbosacral fusion. We secondarily explored the RR for pelvic fixation with instrumentation. We assessed negative control outcomes such as further imaging and major trauma, targeting near-null point estimates. We included adults (≥18 years old) in the TriNetX database from 2005 to 2023 who underwent primary lumbosacral fusion, divided into two cohorts depending on the presence or absence of osteoporosis (ie, osteoporosis and no osteoporosis cohorts) and propensity matched via key risk factors. There were 261 (1.8%) sacral fractures in the entire patient population (n=14,302). Comparing the osteoporosis cohort to no osteoporosis cohort, there was a statistically significant increase in risk of sacral fracture (RR: 1.75 [1.36, 2.24]; p<.001; 166 [2.3%] vs 95 [1.3%] cases), with a median time to event of 154 and 181 days in each cohort, respectively. There was also a statistically significant increase in risk of pelvic fixation with instrumentation (RR: 1.87 [1.25, 2.78]; p=.002). The likelihood of polytrauma (RR=0.98), subdural hemorrhage (RR=1.24), and diagnostic imaging (RR: 0.93) approximated the null between cohorts, suggesting findings would not be explained by differences in these variables. Osteoporosis appears to be independently associated with a statistically and clinically significant risk of sacral fracture through 2 years after lumbosacral fusion. Further research may be warranted for corroboration.