Bin Zheng,* Panfeng Yu,* Haiying Liu, Yan Liang

Spine Surgery, Peking University People’s Hospital, Beijing, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Yan Liang, Email liangyan_spine@163.com

Background: Ankylosing spondylitis (AS) is a chronic autoimmune disease that affects the spine and peripheral joints, often leading to kyphosis, joint stiffness, and even ankylosis. Sagittal parameters, such as total thoracic kyphosis (TTK), thoracic kyphosis (TK), major thoracic kyphosis (MTK), and thoracolumbar kyphosis (TLK), are crucial indices for evaluating spinal alignment in AS patients and can reflect disease progression. This study aims to explore the relationship between bone mineral density (BMD), sagittal parameters, and joint ankylosis in AS patients.
Methods: A retrospective study was conducted on 147 AS patients. Participants were divided into three groups based on cervical and hip joint mobility. BMD was measured using quantitative computed tomography (QCT). Sagittal parameters (TTK, TK, MTK, TLK) were assessed using X-rays. Ordinal multinomial logistic regression and Spearman correlation analyses were performed to identify factors influencing joint stiffness.
Results: Significant differences in age, BMD, and sagittal parameters (TTK, TK, MTK, TLK) were observed among the groups. Ordinal logistic revealed that BMD (Estimate = 0.012) was negatively correlated with joint stiffness, while TTK (Estimate = 0.020) and TLK (Estimate = 0.030) were positively correlated. Age, TK, and MTK do not have a significant impact on joint stiffness. Spearman analysis showed no correlation between BMD and sagittal parameters (TTK and TLK). Besides, TTK and TLK were correlated.
Conclusion: In AS patients, BMD is an independent protective factor against joint stiffness, whereas sagittal parameters (TTK and TLK) contribute to increased joint stiffness. These findings highlight the importance of monitoring both bone mineral density and key sagittal parameters in clinical practice. Early anti-osteoporosis treatment, alongside interventions targeting abnormal spinal alignment, may help preserve joint mobility and potentially prevent progression to joint ankylosis.
Plain Language Summary: BMD is independent protective factor for joint ankylosis in ankylosis spondylitis. It is imperative to start early anti-osteoporosis treatment to preserve cervical and hip mobility.

Keywords: ankylosis spondylitis, BMD, osteoporosis, kyphosis, sagittal parameters