The impact of accurate positioning on measurements made by peripheral QCT in the distal radius.

Summary: Data from pQCT sections at the forearm were examined to assess the impact of positioning on measurements. Two thousand five hundred fifty one scans were analysed. The results showed 25% of scans were not performed in the same anatomical location at follow-up when one section was scanned. These results have implications for accurate follow-up BMD measurements.

Introduction: pQCT of the distal radius is routinely performed using a single section of 2 mm thickness. Accurate positioning is essential to maximise long-term repeatability. We perform two adjacent sections which, permits us to select sections at baseline and follow-up that are in the most similar anatomical site for calculating longitudinal change. This study aimed to assess baseline and follow-up pQCT forearm data to examine variability and determine whether performing two sections, as opposed to one section, improved accuracy when monitoring long-term change in BMD.

Methods: Two adjacent 1.2 mm pQCT radial sections were performed at: baseline n = 2,551 (1,896F:655M) and follow-up n = 335F.

Results: Baseline: difference between adjacent 1.2 mm forearm sections: total BMD 19.3 mg/cm(3) (females) and 16.7 mg/cm(3) (males); trabecular BMD 3.1 mg/cm(3) (females) and 2.35 mg/cm(3) (males); CSA 16.2 mm(2) (females) and 17.7 mm(2) (males) (all significant).

Follow-up: percentage of scans at baseline and follow-up performed in the same anatomical location: one section performed-75%, two sections performed-95%.

Conclusion: When performing a single section at the distal radius it is difficult to perform scans in the same anatomical location at visits. Performing two or more sections can overcome this problem in some individuals and provide more accurate BMD measurements.