The effects of Denosumab on vertebral trabecular and cortical bone mineral density measured by Quantitative Computed Tomography

Introduction: Denosumab is known to increase bone mineral density (BMD) of both trabecular and cortical bones for as long as 10 years. However, no studies have compared the effects of denosumab on trabecular and cortical BMD in the same vertebral body. This study investigated one or more repeated quantitative computed tomography (QCT)s in patients with osteopenia/osteoporosis under the denosumab treatment for up to 8.7 years.

Methods: Patients aged 49 years or older, receiving denosumab regularly for primary osteopenia/osteoporosis, were assessed for vertebral trabecular and cortical BMDs with 1 or more QCTs in LMU Klinikum between 2011 and 2022. Each vertebral trabecular and cortical BMD was measured at the same vertebral level, at the right and left sides, between the 12th thoracic and 5th lumbar vertebrae. The mean value of both sides throughout the measured vertebral bodies was calculated. Any vertebral area with fractures, sclerotic lesions, or artificial devices on QCT was excluded from the BMD measurements. We calculated the correlation coefficient between the vertebral trabecular and cortical BMDs within patients, by using multiple linear regression and two-way repeated measurement analysis of variance test. We applied multivariate linear mixed model to analyze the effect of denosumab on both BMDs over time after denosumab initiation.

Results: A total of 165 patients (143 women and 22 men, mean age 75.6±7.2 years) underwent QCT. Multiple QCTs were performed for 77 patients (65 women and 12 men), and a total of 285 QCTs were evaluated. The first QCT took place between 14 days and 4.5 years (mean 19.4±9.7 months) after denosumab initiation. The longest duration of denosumab treatment at follow-up QCT was 8.7 years. The correlation coefficient between the vertebral trabecular and cortical BMDs within patients was 0.40 (p<0.0001). Multivariate linear mixed model adjusted for age, gender, and time since denosumab initiation, showed that vertebral cortical BMD change per year was -3.60 [95% CI: -5.81 to -1.35] mg/cm³, while vertebral trabecular BMD change per year was +0.72 [95% CI: +0.20 to +1.23] mg/cm³.

Discussion: The vertebral trabecular and cortical BMDs measured within 165 patients showed a moderate positive correlation. For up to 8.7 years since denosumab initiation, our model displayed that vertebral cortical BMD decreased gradually over time, whereas the vertebral trabecular BMD was rather stable. Vertebral BMD has been commonly measured at trabecular region, however the observed discrepancy between the vertebral trabecular and cortical BMDs might suggest the potential role of vertebral cortical BMD in monitoring.

Keywords: Denosumab, Quantitative computed tomography (QCT), Cortical Bone, Trabecular Bone, Spine

Korrespondenzadresse: Saori Harada, LMU Munich, Department of Orthopaedics and Trauma Surgery, Musculoskeletal University Center Munich (MUM), Marchioninistr. 15, 81377 Munich, Deutschland, E-Mail: [e-mail]

Publication History

Article published online:
13 March 2024