Low Trabecular Bone Score Associated With New Bone Formation Independent of Fat Metaplasia in Ankylosing Spondylitis

Researchers evaluated the association between trabecular bone score and new bone formation in ankylosing spondylitis.

Low trabecular bone score (TBS) is associated with new bone formation independent of fat metaplasia on spinal MRI in patients with ankylosing spondylitis (AS), according to study results published in Scandinavian Journal of Rheumatology.

In this study, the researchers aimed to evaluate the association between TBS and new bone formation independently of fatty lesions on spinal MRI, both on a patient and vertebral level.

The study included 68 Korean patients between 2011 and 2015 with AS who underwent spinal MRI and dual-energy x-ray absorptiometry of the lumbar spine to measure TBS and bone mineral density at baseline. Lateral radiographs of the cervical and lumbar spine (baseline and 2 years follow-up) were evaluated for new bone formation, according to the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS). Change in mSASSS from a score of 0 or 1 to 2 or 3 was defined as syndesmophyte formation, and change from a score of 2 to 3 was defined as syndesmophyte growth. Spinal MRIs were evaluated for the presence or absence of fat metaplasia at the first to the fourth lumbar vertebrae.

Results revealed new bone formation in 25% of patients (n=17) at the 2-year follow up. Compared with the control group, the patient group with new bone formation had an increased percentage of fat metaplasia on spinal MRI and an increased number of fat metaplasia occurrences (P =.023 and P =.013, respectively). In addition, patients with new bone formation showed a lower TBS (P =.041) and were more likely to be in the TBS high-risk fracture group at baseline (P =.018). At the patient level, fat metaplasia on MRI and low TBS (<1.23) were significantly associated with new bone formation. At the vertebral level, of the 231 vertebrae in the lumbar spine, new bone formation formed in 25 (11%) after 2 years. Vertebrae with vs without fat metaplasia on MRI at baseline revealed significantly increased new bone formation 24% vs 5%, respectively; P <.001); low TBS also revealed increased new bone formation (32% vs 12%, respectively; P <.001). Syndesmophytes and low TBS independently increased the risk for new bone formation at the vertebral level.

Study limitations included small sample size, confounding interactions, lack of analysis of sequential fat metaplasia occurrence, and the use of statistical analysis, which does not fully reflect correlations between vertebrae from the same patient.

Based on the study findings, the researchers concluded, “This leads us to suggest the possibility of TBS as a predictor of spinal progression in AS.”


Kang KY, Jung J-Y, Lee SK, et al. Trabecular bone score value is associated with new bone formation independently of fat metaplasia on spinal magnetic resonance imaging in patients with ankylosing spondylitis [published online April 21, 2020]. Scand J Rheumatol. doi:10.1080/03009742.2019.1704053