Artificially low cortical bone mineral density in Turner syndrome is due to the partial volume effect

We aimed to show that the decrease in the cortical bone mineral density (BMD) in the radius in Turner syndrome (TS) is artificially caused by the partial volume effect. We confirmed that the partial volume effect-corrected cortical BMD is not decreased in TS compared to in the healthy controls. Other factors are responsible for the increased fracture rate in TS. Introduction Decreased cortical bone mineral density (BMD) has been reported in Turner syndrome (TS), using peripheral quantitative computerised tomography, and it is perceived as one of the major factors leading to increased fracture risk. We tested the hypothesis that low cortical BMD in the radius is caused artificially by the partial volume effect. Methods A cross-sectional study was conducted at the university hospital referral centre between March and October 2013. Thirty-two participants with TS who consented to the study were included (mean age 15.3 +/- 3.2 years). We assessed the cortical BMD in the radius as well as the tibia, where the cortex is thicker compared with the radius. Results Whereas the cortical BMD was decreased in the radius (mean +/- SD Z-score -0.6 +/- 1.5, p = 0.037), it was increased in the tibia (mean Z-score 0.83 +/- 1.0, p < 0.001). After correcting the cortical BMD for the partial volume effect, the mean Z-score was normal in the radius in TS (0.4 +/- 1.3, p = 0.064). The corrected cortical BMD values were similar in the radius and tibia (1108 +/- 52 vs. 1104 +/- 48, group difference p = 0.75). Conclusions The cortical BMD is not decreased in TS. The partial volume effect is responsible for previous findings of decreased cortical BMD in the radius. Altered bone geometry or other factors rather than low cortical BMD likely play a role in the increased fracture risk in TS.