The role of collagen abnormalities in ultrasound and densitometry assessment: In vivo evidence

There is little information concerning how the mutation of collagen affects bone mineralization and the assessment of bone properties. To estimate these influences, we performed ultrasonic assessments of the calcaneus and bone mineral density (BMD) measurements of the hip and lumbar spine. Females with diseases related to the mutation of collagen [Ehlers- Danlos syndrome (EDS) type III and systemic sclerosis (SSc)] participated in this study. We compared the broadband ultrasound attenuation (BUA and UBI- 4), the average transit time through the heel (TTH), and a multiple factor index (UBI-4T) with control subjects matched on age, race, and menstrual status. Both groups of patients had BMD of the spine (L2-L4) within the normal range for their age and sex (for EDS: n = 23, 1.14 ± 0.14 g/cm² and z-score = 0.37; for SSc: n = 15, 0.98 ± 0.15 g/cm² and z-score = 0.20). EDS and SSc subjects had lower BMD of the femoral neck (FN) compared with controls (for EDS: 0.91 ± 0.13 g/cm², z-score = -0.41, P = 0.025; for SSc 0.67 ± 0.13 g/cm², z-score = -0.92, P = 0.006). Subjects with EDS and SSc also had lower BUA values (P = 0.051-0.001) compared with controls. After adjusting for body weight, height, and the level of physical activity, the difference in FN BMD between EDS or SSc and controls became marginal (EDS: P = 0.072; SSc: P = 0.086). However, the significant difference for BUA between subjects and controls remained for EDS (P = 0.008), and disappeared for SSc (0.70) after adjusting for weight, height, level of physical activity, and BMD. These results suggest that the abnormalities of collagen may impact on bone mass measurements differently depending on skeletal site, modality of the assessment, and the source and nature of collagen defects. To determine whether collagen properties influence QUS, proper models in vivo and in vitro should be used.