Added value of distal forearm bone mineral density assessment in routine DXA scanning

Osteoporosis is usually diagnosed by evaluating Bone Mineral Density (BMD) at hip and spine in central DXA (cDXA). In certain cases, cDXA alone may miss patients with BMD loss in cortical bones such as distal radius resulting in underdiagnoses and treatment. We evaluated the incremental role of 33% distal radius BMD/peripheral DXA (pDXA) in correctly classifying the WHO category of BMD which may otherwise be mislabeled on routine cDXA.

Retrospective analysis of 454 DXA scans acquired between January 2018 and July 2024. Patients over 18 years with both cDXA and pDXA, regardless of gender or cancer history, were included. Exclusions included pediatric patients, those on antiresorptive therapy and osseous metastases. BMD at scanned sites, demographics and FRAX risk factors were noted. Descriptive statistics included means and standard deviations for quantitative data, and frequencies with percentages for categorical variables. McNemar's test and logistic regression were used to assess BMD discordance and its predictors. FRAX 10-year major osteoporotic and hip fracture probabilities were calculated using online FRAX tool with pDXA-derived BMD values and compared with cDXA-derived BMD values. Differences in the proportion of patients meeting treatment thresholds were assessed, with statistical significance defined as p < 0.05.

Most patients were females (85%) with mean age of 62 years. Addition of pDXA increased the proportion of patients classified as having osteoporosis from 32% to 46%. Overall, 26% of patients were reclassified to a lower BMD category, most commonly from osteopenia to osteoporosis (73%), followed by normal to osteopenia (10.9%) and normal to osteoporosis (7.6%). Low distal radius BMD was particularly frequent among patients with rheumatoid arthritis and those with multiple osteoporosis risk factors. Comparing routine FRAX risk calculation on cDXA with 33% distal radius (pDXA) BMD, in >50% of patients, there was a statistically significant increase in those qualifying for initiation of bone strengthening treatment (p-value = 0.04).

The addition of pDXA to existing cDXA protocols led to worsening of WHO BMD category in one in four of our population, highlighting the value of including 33% distal radius in bone health evaluation especially in women, elderly, patients with rheumatoid arthritis, and those with multiple FRAX risk factors. Using pDXA BMD value in FRAX calculation increases the predicted likelihood of major osteoporotic and/or hip fracture and therefore would have a significant impact on treatment.