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Long-term immobilization in elderly females causes a specific pattern of cortical bone and osteocyte deterioration different from postmenopausal osteoporosis.

J Bone Miner Res. 2020 Jan 30;: Authors: Rolvien T, Milovanovic P, Schmidt FN, von Kroge S, Wölfel EM, Krause M, Wulff B, Püschel K, Ritchie RO, Amling M, Busse B

Immobilization as a result of long-term bed rest can lead to gradual bone loss. Due to their distribution throughout the bone matrix and remarkable interconnectivity, osteocytes represent the major mechanosensors in bone and translate mechanical into biochemical signals controlling bone remodeling. To test whether immobilization affects the characteristics of the osteocyte network in human cortical bone, femoral diaphyseal bone specimens were analyzed in immobilized female individuals and compared to age-matched postmenopausal individuals with primary osteoporosis. Premenopausal and postmenopausal healthy individuals served as control groups. Cortical porosity, osteocyte number and lacunar area, the frequency of hypermineralized lacunae as well as cortical bone calcium content (CaMean) were assessed using bone histomorphometry and quantitative backscattered electron imaging (qBEI). Bone matrix properties were further analyzed by Fourier transform infrared spectroscopy (FTIR). In the immobilization group, cortical porosity was significantly higher, and qBEI revealed a trend towards higher matrix mineralization compared to osteoporotic individuals. Osteocyte density and canalicular density showed a declining rate from premenopausal towards healthy postmenopausal and osteoporotic individuals with peculiar reductions in the immobilization group, while the number of hypermineralized lacunae accumulated inversely. In conclusion, reduced osteocyte density and impaired connectivity during immobilization are associated with a specific bone loss pattern, reflecting a phenotype clearly distinguishable from postmenopausal osteoporosis. Immobilization periods may lead to a loss of survival signals for osteocytes, provoking bone loss that is even higher than in osteoporosis states, while osteocytic osteolysis remains absent. This article is protected by copyright. All rights reserved. PMID: 31999373 [PubMed - as supplied by publisher]

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