Журнал «Боль. Суставы. Позвоночник» 3 (15) 2014

Статья опубликована на с. 90

Osteoporosis is a skeletal disorder characterized by low bone strength and increased fracture risk. Bone mineral density (BMD) is considered the standard measurement for the diagnosis of osteoporosis. In daily clinical routine, it is evaluated by dual-energy X-ray absorptiometry (DXA). Patients who sustain osteoporosis-related fragility fractures have reduced bone mass and alterations in their bone structure. However, most of the fragility fractures occur in patients with osteopenia or even normal BMD, suggesting that BMD is of limited benefit in fracture risk prediction. In addition, there is a considerable overlap in BMD values of patients with and without fractures.This suggests that BMD alone is not a reliable indicator of the factors that contribute to fracture risk. Several factors are known to influence bone strength and fracture risk, including the anatomic dimensions of cortical bone, the microstructure of trabecular bone, microdamage, as well as bone mineralisation and turnover. To address these issues, advanced analytical methods have been invented to assess cortical and trabecular microarchitecture separately, most precisely by invasive methods, such as transiliac biopsies. In clinical routine, transiliac biopsies are restricted to untypical, unclear and complicated cases in the diagnosis of osteoporosis, since it is an invasive procedure. Furthermore, there have been doubts whether the iliac crest is a representative site. Among noninvasive techniques, high resolution peripheral quantitative computed tomography (HR-pQCT) and magnetic resonance imaging (MRI) allow direct measurement of the bone microarchitecture. However these two methods remain unsuitable for routine screening due to high costs, the availability of devices or the lack of validation studies. Therefore, Trabecular Bone Score (TBS), a new grey-scale textural analysis to estimate trabecular microarchitecture from the anterior/posterior (AP) Spine DXA, has been introduced. It is a texture measurement that can be applied to any X-ray image, including DXA images, by quantifying variations in grey levels using the experimental variogram approach. TBS is able to differentiate between 3D microarchitectures that exhibit the same BMD but different trabecular characteristics. The benefit of TBS in addition to BMD for fracture risk assessment has been documented in several cross-sectional and prospective studies. On the structural level of bone tissue significant correlations have been identified between TBS and 3D parameters of bone microarchitecture independent of any correlation between TBS and BMD. The analysis was performed however in human cadaver vertebrae. The aim of this cross-sectional study was to evaluate correlations between TBS of the spine and microarchitectural parameters of transiliac bone biopsies in females with idiopathic osteoporosis and fragility fractures. As a result, the clinical impact and precision of TBS in bone quality assessment was evaluated. The following structural parameters of transiliac bone biopsies from 12 treatment-naіve and otherwise healthy females (mean 47; range 34 to 69.5 years) with fragility fractures were analyzed by a microtomographic imaging system: Bone volume/total volume (BV/TV), trabecular thickness (TbTh), trabecular separation (TbSp), number of trabeculi (TbN), connectivity density (ConnD) and structure model index (SMI). Spine BMD was assessed by DXA and site-matched spine TBS parameters were extracted from the DXA image using the TBS iNsight calculator. Laboratory tests did not reveal any evidence of metabolic disorder in any of our subjects. There was a correlation between TBS and the following 3D parameters: TBS and BV/TV: r = 0.70 (p < 0.01), TBS and TbSp: r = –0.70 (p < 0.01), TBS and TbN: r = 0.58 (p < 0.05), and TBS and SMI: r = –0.75 (p < 0.01). Even after adjustment for spine BMD, the correlation between TBS and BV/TV, TbN, TbSp and SMI remained significant. Using the stepwise regression approach the best models combining density and microarchitecture predicted 97% of the TBS parameters. The association between TBS and microarchitectural parameters indicated that low TBS showed a marked deteriorated microarchitecture related to low TbN, high TbSp, altered SMI as well as low BV/TV. Hence, TBS is a reliable tool for assessment of the trabecular tissue structure in transiliac bone biopsies.