Surgical outcomes following spinal fusion for cervical versus noncervical fractures in ankylosing spondylitis and DISH.

Background: Ankylosing spondylitis (AS) and diffuse idiopathic skeletal hyperostosis (DISH) are 2 distinct spondyloarthropathies characterized by progressive spinal ankylosis. Despite their differing pathophysiologies, both conditions create long rigid spinal segments that are vulnerable to unstable fractures. Although the existing literature often examines postoperative outcomes of either AS or DISH-related fractures, direct comparisons between the 2 disorders remains limited. This study aims to compare 3-month, 1-year, and 2-year outcomes following spinal fusion for cervical and noncervical fractures in patients with AS and DISH. Methods: This was a retrospective cohort study. The TriNetX Global Collaborative Network database was queried using ICD-10 and CPT codes to identify adult patients (≥18 years) diagnosed with either AS or DISH who underwent spinal fusion surgery following cervical or noncervical fractures spinal fractures within the past twenty years. Propensity score matching (1:1) was performed using demographic variables and relevant comorbidities. Postoperative complications were assessed at 3-month, 1-year, and 2-year intervals and included medical, surgical, and infection-related outcomes. All statistical analyses were performed within the TriNetX platform, and a p-value < .05 was considered statistically significant. Results: Among AS patients, the cervical group exhibited a significantly lower rate of surgical site infections (SSI) at 3 months (RR 0.44, p = .016), reduced thromboembolic events (RR 0.53, p = .03) at 2 years compared with AS patients with a noncervical fractures fracture. For both AS and DISH patients, cervical fractures were significantly associated with increased risk of spinal cord injury at all time points. In DISH patients, postoperative limb paralysis was also significantly higher following cervical fracture and fixation at all time points. Comparing all AS versus DISH patients, AS was associated with significantly higher mortality at 3 months (RR 2.16, p < .001), 1 year (RR 1.77, p < .001), and 2 years (RR 1.73, p < .001). Instrumentation failure was more common in AS patients at 1 year (RR 2.27, p = .018) and 2 years (RR 1.93, p = .032). Interestingly, pseudoarthrosis was significantly less common in AS compared to DISH at 1 year (RR 0.58, p = .006) and 2 years (RR 0.59, p = .0065). Conclusions: Cervical fractures in both AS and DISH patients showed a higher risk of SCI compared to noncervical fractures, likely secondary to the narrowing of the canal within this region. Overall, AS patients had higher rates of mortality, instrumentation failure, and wound complications compared to those with DISH, while DISH patients had higher rates of pseudoarthrosis.