Bone mineral density of the ultra-distal radius: are we ignoring valuable information?

Associations between ultra-distal forearm bone mineral density and incident fracture in women

Bone mineral density measured at the ultra-distal forearm site was associated with any fracture, as well as distal radius fracture in women from a longitudinal cohort study.

PURPOSE

Femoral neck (BMDhip) and lumbar spine (BMDspine) bone mineral density (BMD) are routinely used to assess fracture risk. More data are needed to understand how ultra-distal forearm BMD (BMDUDforearm) may assist fracture prediction.

METHODS

Using a Lunar DPX-L, Geelong Osteoporosis Study women (n = 1026), aged 40-90 years, had BMD measured. Incident low-trauma fractures were radiologically verified. Using Cox proportional hazard models, hazard ratios (HR) were calculated for BMDUDforearm as a continuous variable (expressed as a one-unit decrease in T-score) and a categorical variable (normal/osteopenia/osteoporosis). Areas under receiver operating characteristics (AUROC) curves were calculated. Analyses were conducted for any fracture and distal radius fractures.

RESULTS

During 14,270 person-years of follow-up, there were 318 fractures (85 distal radius). In adjusted models, continuous BMDUDforearm was associated with any (HR 1.26;95%CI 1.15-1.39) and distal radius fractures (HR 1.59;95%CI 1.38-1.83). AUROCs for continuous BMDUDforearm, 33% forearm(BMD33%forearm), BMDhip, BMDspine, and FRAX without BMD were similar for any fracture (p > 0.05). For distal radius fracture, the AUROC for BMDUDforearm was higher than other sites and FRAX (p < 0.05). In adjusted models, those with osteoporosis had a higher likelihood of any fracture (HR 2.12; 95%CI 1.50-2.98). For distal radius fractures, both osteopenia and osteoporosis had a higher risk (HR 4.31; 95%CI 2.59-7.15 and 4.81; 95%CI 2.70-8.58). AUROCs for any fracture were similar for categorical BMD at all sites but lower for FRAX (p < 0.05). For distal radius fractures, the AUROC for BMDUDforearm, was higher than other sites and FRAX (p < 0.05).

CONCLUSION

Ultra-distal forearm BMD may aid risk assessments for any distal radius fractures.

The effect of forearm rotation on the bone mineral density measurements of the distal radius

INTRODUCTION

Forearm dual-energy X-ray absorptiometry (DXA) is often performed in clinics where central DXA is unavailable. Accurate bone mineral density (BMD) measurement is crucial for clinical assessment. Forearm rotation can affect BMD measurements, but this effect remains uncertain. Thus, we aimed to conduct a simulation study using CT images to clarify the effect of forearm rotation on BMD measurements.

MATERIALS AND METHODS

Forearm CT images of 60 women were analyzed. BMD was measured at the total, ultra-distal (UD), mid-distal (MD), and distal 33% radius regions with the radius located at the neutral position using digitally reconstructed radiographs generated from CT images. Then, the rotation was altered from - 30° to 30° (supination set as positive) with a one-degree increment, and the percent BMD changes from the neutral position were quantified for all regions at each angle for each patient.

RESULTS

The maximum mean BMD changes were 5.8%, 7.0%, 6.2%, and 7.2% for the total, UD, MD, and distal 33% radius regions, respectively. The analysis of the absolute values of the percent BMD changes from the neutral position showed that BMD changes of all patients remained within 2% when the rotation was between - 5° and 7° for the total region, between - 3° and 2° for the UD region, between - 4° and 3° for the MD region, and between - 3° and 1° for the distal 33% radius region.

CONCLUSION

Subtle rotational changes affected the BMD measurement of each region. The results showed the importance of forearm positioning when measuring the distal radius BMD.