Microarchitectural caracterisation of trabecular bone in metastatic patients using micro-computed tomography
Résumé
Introduction Bone metastases in oncologic patients cause increasing fracture risk and impair their quality of life. The most frequent site of pathological fractures are vertebrae and proximal femur. Numerical models were developed to estimate the fracture risk and guide prophylactic fixation [1]. Previous reported studies showed altered mechanical properties in metastatic vertebrae [2], but few studied specifically the proximal femur [3]. As femoral bone presents a specific pattern of trabeculae, a better comprehension of bone architecture in pathologic areas could be a key element to estimate their mechanical properties, to incorporate them into numerical models. The aim of this study was to characterize the microarchitecture of metastatic and normal femoral bone. Methods After ethical approval, 5 human proximal femurs were harvested during a prosthetic replacement performed for a lytic bone metastasis (Figure 1). All patients presented a known solid cancer or a multiple myeloma. Each sample was dehydrated and fixed in ethanol and scanned at 9 μm using a micro-CT device (Skyscan® 1176, Brucker, Kontich Belgium, 50kV, 500μA, Al 0.5mm filter). Microarchitectural parameters, namely bone volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), connectivity, and Structure Model Index (SMI) were evaluated on 3 specimens and compared in the normal and the metastatic area of each sample. Results As intended, BV/TV was lower in metastatic areas (2.3% [0.1-6.5%] vs 28.3% [19.4-44.7%]) (Figure 2). Trabeculae were thinner (89μm [76-98μm] vs 192μm [157-221μm]) and more separated (1167μm [411-1852μm] vs 370μm [231-481μm]) than the normal bone. Connectivity was lower (355 [7-1024] vs 3365[225-6803]) and the SMI showed more “plates” than “rods” in the metastatic area (2.8 [2.6-3.0] vs 1.8 [1.8-1.9]). Discussion Mechanical properties used in numerical models are frequently estimated using bone density. Nevertheless, this is not the only parameter determining bone resistance, as shown in osteoporotic patients [4]. Microarchitectural parameters need to be assessed in metastatic patients and linked to mechanical properties. More results are needed to confirm these data. Because of the different bone pattern in the different regions of the proximal femur, it may be necessary to evaluate separately the microarchitectural parameters depending of the localization of the metastasis. Metastatic invasion of the bone tissue involves focal areas on lysis, surrounded by a border area with intermediate bone alteration. A better comprehension of the modifications of the bone pattern in these regions can improve the reliability of our numerical models. References 1. Eggermont et al, Bone, 130:115101, 2020 2. Bailey et al, J Bone Miner Res 37(5):896-907, 2022. 3. Kochetkova et al, Bone 177, 2023. 4. Aaron et al, Clin Orthop Relat Res 215:260-71, 1987
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