Femur Bone Mineral Density and Pentosidine Level Distinguish Ankylosing Spinal Disorder Patients with and without Sacroiliac Ankylosis

Introduction: When spinal fracture occurred in ankylosing spinal disorder (ASD) patients, it is important to evaluate not only the long lever arm but also bone density and bone quality for the determination of treatment strategies. This case-controlled study examined bone mineral density (BMD), bone metabolism markers, and pentosidine levels in patients with ASD.Methods: Subjects with bridging of minimum four contiguous vertebral bodies were classified into ASD group and the rest into non-ASD group. The former was further divided into two subgroups based on the presence/absence of sacroiliac joint ankylosis (SJA). We compared BMD, bone metabolism markers, and pentosidine levels in these groups.Results: The BMD T and Z scores of the femur proximal extremity were lower in the ASD with SJA group than those in the ASD without SJA group. When groups were matched for age, weight, and eGFR, compared with the non-ASD group, the ASD with SJA group had lower BMD of the lumbar spine and femur proximal extremity and the ASD without SJA group had significantly higher BMDs of the lumbar spine and femur proximal extremity. After matching, the ASD without SJA group showed a significantly higher pentosidine level than the non-ASD group.Conclusions: Patients with SJA have low femur proximal extremity BMD, whereas those with ASD without SJA have a higher BMD of the femur proximal extremity with high pentosidine level. Investigating the presence or absence of SJA is important for the determination of treatment strategies in fractured ASD patients.