Within the mineralized bone, osteocytes form a multifunctional mechanosensitive network orchestrating bone remodelling. A preserved osteocyte population is a crucial determinant of bone quality. In human auditory ossicles, the early decrease in osteocyte numbers but maintained integrity remains an unexplained phenomenon that might serve for sound transmission from air to the labyrinth. Here we analysed the frequency, size and composition of osteocyte lacunae in the auditory ossicles of 22 individuals from early postnatal period to old age. Mineralization of the bone matrix was determined using backscattered electron imaging. No signs of bone remodelling were observed above the age of 1 year. We detected characteristics of early bone tissue aging, such as decrease in osteocytes, lower total lacunar density and lacunar area, as well as high matrix mineralization accompanied by distinct accumulation of micropetrotic lacunae and decreased indentation depths. The majority of these changes took place in the first months and years of life, while afterwards only minor reorganization was present. With osteocyte apoptosis potentially being a consequence of low mechanical stimuli, the early loss of osteocytes without initiation of bone remodelling indicates an adaptive response conserving the architecture of the auditory ossicles and ensuring stable sound transmission throughout life.The human auditory ossicles malleus, incus and stapes present with their final morphology at birth, while in later life decades only minor morphological changes occur 1 . The ossicles are located in the air-filled middle ear and serve for transmission of sound-induced mechanical vibrations from the eardrum to the oval window of the fluid-filled cochlea 2 . Damage or deformation of the ossicular chain lead to conductive hearing loss 3 . While malleus and incus develop from the first pharyngeal arch, the stapes which is the smallest bone in the human body has two embryologically distinct parts. In fact, the cranial end of the second pharyngeal arch forms an independent anlage, which develops into a superior and an inferior part. The superior part gives origin to the base of the stapes, whereas the inferior part forms the limbs (anterior and posterior crus) and the head of the stapes 4 . As sound transmission is the major function of the auditory ossicles and biomechanical loads are minor 5 , adaptive bone remodelling might be unnecessary here. In general, the absence of bone remodelling as seen with aging would be associated with hypermineralization of the bone matrix itself, but also with the accumulation of hypermineralized (micropetrotic) osteocyte lacunae 6,7 . The latter describes the in vivo formation of intra-lacunar calcification 8 , which is believed to follow apoptosis of some osteocytes 7 . Hypermineralized osteocyte lacunae accumulate in aged 6 , osteoporotic 9 and osteoarthritic 10 bone. In the ossicles, increased numbers of dead osteocytes as a sign of impaired bone remodelling have been reported 11,12 , however the degree of miner...

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Background:Total hip arthroplasty (THA) is frequently accompanied by acetabular bone loss, which constitutes a major challenge in revision procedures. Structural allografts can be implanted to restore a stable osseous foundation for the acetabular prosthesis. As previous studies were limited to clinical data or included very few cases, the extent to which the graft bone is incorporated over time has remained unclear.Methods:Thirteen acetabula were retrieved post mortem, and the incorporation properties of the bone allografts were analyzed using a hierarchical approach of imaging techniques including contact radiography, high-resolution peripheral quantitative computed tomography (HR-pQCT), histological analysis of undecalcified specimens, and quantitative backscattered electron imaging (qBEI). The distance between the current allograft bone and host bone borders (i.e., current overlap) as well as the distance between the original allograft bone and host bone borders (i.e., total ingrowth) were assessed.Results:In 10 of 13 cases, the complete interface (100%) was characterized by direct contact and additional overlap of the allograft bone and host bone, while the remaining 3 cases demonstrated direct contact along 25% to 80% of the interface. The allograft bone showed an intact trabecular structure and significantly higher mineralization compared with the host bone. The mean current overlap (and standard deviation) was 2.3 ± 1.0 mm, with a maximum of 5.3 ± 2.4 mm. Importantly, the total ingrowth reached much further, to a mean of 7.2 ± 2.3 mm (maximum, 10.5 ± 4.0 mm). Neither the time that the allograft was in situ nor the degree of contact between the host and allograft bone correlated with the current overlap and the time in situ did not correlate with total ingrowth.Conclusions:This study showed bone remodeling with subsequent interconnection of the host and allograft bone along the majority of the interface, leading to adequate incorporation of the allograft. The lack of complete incorporation of the graft did not lead to graft collapse up to 22 years after revision surgery.Clinical Relevance:Our study provides the first systematic multiscale evaluation of successfully implanted structural allografts and forms the scientific basis for their clinical use in revision THA.