Maximum number of bone cross-linked vertebrae: an index for BMD in diffuse idiopathic skeletal hyperostosis

Introduction: The maximum number of vertebral bodies with bony bridges between adjacent vertebrae (max VB) helps assess the risk of fracture in diffuse idiopathic skeletal hyperostosis (DISH). In addition to max VB, the maximum thickness of bone cross-bridges (max TB) may be an index of bone mineral density (BMD). Therefore, this study investigated the relationship among max VB, max TB, and BMD. Materials and methods: The participants in this cross-sectional study were male patients (n = 123) with various max VB from the thoracic vertebrae to the sacrum without sacroiliac ankylosis. The participants were grouped by max VB. For example, a group with max VB from 4 to 8 would be listed as max VB (4–8). The relation between femur proximal BMD and mean max TB and max VB was assessed. Femur proximal BMD was then compared after adjusting for confounding factors. Results: The results indicated that max VB was correlated with femur proximal BMD in max VB (0–8) and max VB (9–18) groups. The mean max TB was correlated only with femur proximal BMD in max VB (0–8). After adjusting, max VB (4–8) showed a significantly higher femur proximal BMD than max VB (0–3) and max VB (9–18). Conclusion: Femur proximal BMD and mean max TB showed different trends after max VB = 9, which suggests that max VB is an index of BMD, and that DISH has at least two possible populations in terms of BMD and bone cross-link thickness.