Why Preventing Osteoporosis of the Spine Needs a Different Approach

Findings from a study presented at ACR 2020 showed a clear difference in co-morbidities and medication use associated with osteoporosis at different lumbar levels. Here, a Q&A with the co-author.

Risk factors for low bone mineral density (BMD) are not equal throughout the lumbar spine and differ from traditional osteoporotic risk factors for osteoporosis of the hip, according to investigators reporting at the annual meeting of the American College of Rheumatology.

The team said its findings highlight the need to consider risk factors specific to lumbar spine osteoporosis when planning prevention and management of vertebral fragility fractures.

BMD measurements at the hip are used to predict fracture risk using tools like FRAX. As dual energy X-ray absorptiometry (DEXA) can be used to measure BMD at lumbar vertebrae, the investigators set out to determine whether predictors of hip osteoporosis and fracture mimic those for vertebral osteoporosis.

In this Q&A, study co-author Mrinalini Dey, MB, BChir, MA, MRCP, NIHR Academic Clinical Fellow at the Institute of Life Course and Medical Sciences, University of Liverpool, and Registrar in Rheumatology at Aintree University Hospital, Liverpool, UK, discusses the findings.

The study included 26119 female patients, with an average age of 65 years, presenting for BMD estimation in North West England between 2004 and 2016. In addition to BMD in L1-4, demographics, fracture history, and risk factors were recorded. Logistic regression models at each lumbar vertebral level were used to identify predictors of osteoporosis (T-score≤-2.5).

The results showed a clear difference in co-morbidities and medication use associated with osteoporosis at different lumbar levels and that traditional risk factors for osteoporosis were not associated with decreased BMD in the lumbar spine. Patients with vertebral osteoporosis were more likely to sustain fragility fractures as expected.

Hormone replacement therapy is bone-protective and was associated with significantly decreased likelihood of osteoporosis. Current aromatase inhibitor use also was associated with decreased likelihood of osteoporosis at all lumbar levels, and current corticosteroid use was associated with decreased likelihood of osteoporosis in the lower lumbar region. Both medications are known to reduce BMD, but the results were confounded by concurrent use of calcium, vitamin D, and bisphosphonate treatment.

Systemic lupus erythematosus (SLE) was associated with reduced likelihood of osteoporosis at the superior and inferior lumbar spine, but this finding was also likely confounded by treatment. Consistent with previous studies current hyperthyroidism was associated with significantly increased risk of osteoporosis averaged across the spine, while current alcohol intake was associated with decreased risk of osteoporosis at L3.

Rheumatology Network: Why was the study conducted?

Mrinalini Dey, MB, BChir, MA, MRCP: The most common site of osteoporotic fragility fractures is the thoracic spine, but it is not known if predictors of hip osteoporosis and fracture mimic those for vertebral osteoporosis. We therefore aimed to evaluate factors associated with osteoporosis in the lumbar spine in female patients presenting for BMD estimation.

We conducted a large retrospective observation cohort study in patients presenting for bone mineral density estimation at a district general hospital in North West England over a period of twelve years, using logistic regression models to identify patient, disease and drug factors associated with vertebral osteoporosis.

RN: What is the most important take home from this study for rheumatologists?

Dey: Our main finding from this study is that traditional risk factors for osteoporosis at the hip are not associated with decreased BMD in the lumbar spine.

RN: Why do you think this was the case?

Dey: It is likely that the difference in risk factors is due to the difference in bone structure between the hip and vertebrae, i.e. trabecular vs cortical bone.

The vertebrae are one of the most common sites of osteoporotic fragility fractures. Our study indicates that further research is needed on the risk factors for vertebral osteoporosis, especially in light of the prevalence of fragility fractures affecting the spine. Larger clinical trials as a result of observational studies such as ours are likely to provide the evidence required to change the way in which we assess fracture risk in the spine compared to the hip.

RN: Did anything surprise you about the findings?

Dey: We were surprised to find an association between certain conditions and decreased likelihood of osteoporosis at various lumbar levels, including systemic lupus erythematosus (SLE) and hyperthyroidism. Aromatase inhibitor use and corticosteroid use were also associated with decreased likelihood of osteoporosis. However, in both cases it is important to remember that this is an observational study and therefore association does not equate with causality. Secondly, we did not have access to information on treatment with vitamin D supplementation, for example, and the dose and duration of all drugs, which are likely to have confounded these results.

RN: What are the future implications for practice of your findings?

Dey: We have demonstrated in this large observational study, that risk factors for low bone mineral density are not equal throughout the lumbar spine, and differ from traditional osteoporotic risk factors, including those commonly used in predictive scores for fracture. Established scoring systems are based on bone mineral density at the hip. Our results suggest a need to consider risk factors specific to lumbar spine osteoporosis when planning prevention and management of vertebral fragility fractures, although, larger clinical trials are needed in order to inform this change in clinical practice.

Osteoporosis and fragility fractures constitute a large burden of morbidity and mortality worldwide. Through this work, and in previous studies, we have demonstrated the utility in using real-world observational data in order to identify possible predictors of osteoporosis and fragility fracture in at-risk populations.2,3 Such research can help to inform policy determining prophylaxis and management of fragility fractures, and inform the need for larger clinical trials in this area.

REFERENCES:

1. ABSTRACT 0544. “Risk Factors for Lumbar Vertebral Osteoporosis Do Not Reflect Factors Traditionally Associated with Osteoporosis at the Hip.” The annual meeting of the American College of Rheumatology. 9:00 AM, Saturday, Nov. 7, 2020.

2. Dey M, Bukhari M. OP0294 Differential influence of co-morbidities on site of fragility fractures. Ann Rheum Dis [Internet]. 2020;79(Suppl 1):183. Available from: https://ard.bmj.com/content/79/Suppl_1/183.2

3. Dey M, Bukhari M. Predictors of fragility fracture and low bone mineral density in patients with a history of parental fracture. Osteoporos Sarcopenia [Internet]. 2019 Mar 15 [cited 2019 Mar 15]; Available from: https://www.sciencedirect.com/science/article/pii/S240552551830205X?via%3Dihub