Background Rheumatoid arthritis (RA)is a well known risk factor for osteoporosis (OO) and is an independent risk factor in the FRAX ™ tool, additionally the femoral neck Bone mineral density (BMD) is included in the tool as a risk factor for fracture, but not the lumbar spine.
Objectives To determine the predictors of fragility fractures in an observational cohort of patients with RA referred for BMD estimation, and whether using lumbar spine BMD would predit risk.
Methods Patients referred for BMD estimation in a scanner in the North west of England between 2004 and 2014 with a history of RA were identified from a dual X-ray absorptiometry (DEXA) database. Demographics and other risk factors were also recorded. Fragility fractures were also recorded. Initially those who had sustained a fracture were compared to those who had not sustained a fracture using chi squared test for categorical variables and Student's T test for continous variables. Subsequently univariate and multivariate logistic regression models were fitted. Variables included age at scan, gender, weight, height and body mass index (BMI),family history of fracture, alcohol, smoking, current steroid exposure, causes of secondary OP as per the FRAX™ definition, in addition to BMD in the lumbar spine (L1-L4) and the non-dominant femoral neck.
Results 1527 patients were scanned in the referral period. Mean age at scan was 64.3 year (SD 11.6), 1207 (79.0%) were female, 406 (26.6%) had sustained a fracture. Patients who had sustained a fracture were more likely to be female 347/860 (28.8%) vs 59/320 (18.4%) (p<0.001) and older 65.6 years (SD11.6) vs 63.9 years (SD11.5) (p=0.01). They also had lower BMD in the lumbar spine and the femoral neck. Results of the univariate analysis unadjusted and adjusted for age and gender are shown in table 1 with significant predictors marked with an asterisk (*).
In the multivariate model, the variables that predicted fractures in this cohort the BMD in the lumbar spine (OR 0.33 95%CI 0.14,0.80), BMD in the femoral neck (OR 0.29 95%CI 0.09,0.94)and alcohol excess (OR 2.01 95%CI 1.12,3.61)family history (OR 1.49 95%CI 1.01,2.19)and secondary osteoporosis (OR 1.50 95%CI 1.03,2.18). Using the lumbar spine only gave an area under the curve (AUC) of the model of 0.640 whilst using the lumbar spine only gave an AUC of 0.633, using both gave an AUC of 0.646.
Conclusions In univariate analysis, many risk factors are associated with fracture in this cohort with RA. Using the lumbar spine BMD improved the prediction of fractures, this is not included in the FRAX™ tool and would underestimate the fracture risk in this cohort. Further models including the L1l4 BMD should be developed to more accurately predict fractures in patients with RA.
Disclosure of Interest None declared