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A two-stage model is proposed for investigating remodelling characteristics in bone over time and distance to the growth plate. The first stage comprises a partial differential equation (PDE) for bone density as a function of time and distance from the growth plate. This stage clarifies the contributions to changes in bone density due to remodelling and growth processes and tracks the rate at which new bone emanates from the growth plate. The second stage consists of simulating the remodelling process to determine remodelling characteristics. Implementing the second stage requires the rate at which bone moves away from the growth plate computed during the first stage. The second stage is also needed to confirm that remodelling characteristics predicted by the first stage may be explained by a realistic model for remodelling and to compute activation frequency. The model is demonstrated on microCT scans of tibia of juvenile female rats in three experimental groups: sham-operated control, oestrogen deprived, and oestrogen deprived followed by treatment. Model predictions for changes in bone density and remodelling characteristics agree with the literature. In addition, the model provides new insight into the role of treatment on the density of new bone emanating from the growth plate and provides quantitative descriptions of changes in remodelling characteristics beyond what has been possible to ascertain by experimentation alone., (© 2024. The Author(s).)

This preliminary study quantified tibia cartilage thickness (Cart.Th), subchondral bone plate thickness (SBPl.Th) and subchondral trabecular bone (STB) microarchitecture in subjects with varus‐ or valgus‐ malaligned knees diagnosed with end‐stage knee osteoarthritis (OA) and compared them to controls (non‐OA). Tibial plateaus from 25 subjects with knee‐OA (undergoing knee arthroplasty) and 15 cadavers (controls) were micro‐CT scanned (17 µm/voxel). Joint alignment was classified radiographically for OA subjects (varus‐aligned n = 18, valgus‐aligned n = 7). Cart.Th, SBPl.Th, STB bone volume fraction (BV/TV) and their medial‐to‐lateral ratios were analyzed in anteromedial, anterolateral, posteromedial and posterolateral subregions. Varus‐OA and valgus‐OA were compared to controls. Compared to controls (1.19–1.54 mm), Cart.Th in varus‐OA was significantly lower anteromedially (0.58 mm, −59%) and higher laterally (2.19–2.47 mm, +60–63%); in valgus‐OA, Cart.Th was significantly higher posteromedially (1.86 mm, +56%). Control medial‐to‐lateral Cart.Th ratios were around unity (0.8–1.1), in varus‐OA significantly below (0.2–0.6) and in valgus‐OA slightly above (1.0–1.3) controls. SBPl.Th and BV/TV were significantly higher medially in varus‐OA (0.58‐0.72 mm and 37–44%, respectively) and laterally in valgus‐OA (0.60–0.61 mm and 32–37%), compared to controls (0.26–0.47 mm and 18–37%). In varus‐OA, the medial‐to‐lateral SBPl.Th and BV/TV ratios were above unity (1.4–2.4) and controls (0.8–2.1); in valgus‐OA they were closer to unity (0.8‐1.1) and below controls. Varus‐ and valgus‐OA tibia differ significantly from controls in Cart.Th, SBPl.Th and STB microarchitecture depending on joint alignment, suggesting structural changes in OA may reflect differences in medial‐to‐lateral load distribution upon the tibial plateau. Here we identified an inverse relationship between cartilage thickness and underlying subchondral bone, suggesting a whole‐joint response in OA to daily stimuli. [ABSTRACT FROM AUTHOR]

Primary press-fit fixation of femoral knee prostheses is obtained thanks to the inside dimensions of the implant being undersized with respect to the bone cuts created intra-operatively, dictated by a press-fit specified by the implant design. However, during prostheses press-fit implantation, high compressive and shear stresses at the implant-bone interface are generated, which causes permanent bone damage. The extent of this damage is unknown, but it may influence the implant stability and be a contributing factor to aseptic loosening, a main cause of revisions for knee arthroplasty. The aim of this ex-vivo study was to quantify, using high-resolution peripheral quantitative computed tomography (HR-pQCT) imaging and Digital Volume Correlation (DVC), permanent bone deformation due to press-fit femoral knee implantation of a commonly used implant. Six human cadaveric distal femora were resected and imaged with HR-pQCT (60.7 μm/voxel, isotropic). Femurs were fitted with cementless femoral knee implants (Sigma PFC) and rescanned after implant removal. For each femur, permanent deformation was examined in the anterior, posterior-medial and posterior-lateral condyles for volumes of interest (VOIs) of 10 mm depth. The bone volume fraction (BV/TV) for the VOIs in pre- and post-implantation images was calculated, at increasing depth from the bone surface. DVC was applied on the VOIs pre- and post-implantation, to assess trabecular bone displacements and plastically accumulated strains. The "BV/TV post /BV/TV pre ratio vs. depth" showed, consistently among the six femurs, three consecutive points of interest at increasing bone depth, indicating: bone removal (ratio<100%), compaction (ratio>100%) and no changes (ratio = 100%). Accordingly, the trabecular bone displacement computed by DVC suggested bone compaction up to 2.6 ± 0.8 mm in depth, with peak third principal strains of −162,100 ± 55,000 με (mean absolute error: 1,000–2,000 με, SD: 200–500 με), well above the yield strain of bone (7,000–10,000 με). Combining 3D-imaging, at spatial resolutions obtainable with clinical HR-pQCT, and DVC, determines the extent of plastic deformation and accumulated compressive strains occurring within the bone due to femoral press-fit implantation. The methods and data presented can be used to compare different implants, implant surface coatings and press-fit values. These can also be used to advance and validate computational models by providing information about the bone-implant interface obtained experimentally. Future studies using these methods can assist in determining the influence of bone damage on implant stability and the subsequent osseointegration. Image 1 • Permanent bone deformation is generated due to press-fit femoral knee implantation. • HR-pQCT and DVC can quantify the generated plastic bone deformation. • "BV/TV post /BV/TV pre ratio" showed 3 points of interest at increasing bone depth: • Bone removal (ratio<100%), compaction (ratio>100%), unchanged (ratio = 100%). • DVC confirms bone compaction; peak 3rd principal strains above yield strain of bone. [ABSTRACT FROM AUTHOR]

ABSTRACT Tibial subchondral bone plays an important role in knee osteoarthritis (OA). Microarchitectural characterization of subchondral bone plate (SBP), underlying subchondral trabecular bone (STB) and relationships between these compartments, however, is limited. The aim of this study was to characterize the spatial distribution of SBP thickness, SBP porosity and STB microarchitecture, and relationships among them, in OA tibiae of varying joint alignment. Twenty-five tibial plateaus from end-stage knee-OA patients, with varus ( n = 17) or non-varus ( n = 8) alignment were micro-CT scanned (17 μm/voxel). SBP and STB microarchitecture was quantified via a systematic mapping in 22 volumes of interest per knee (11 medial, 11 lateral). Significant within-condylar and between-condylar (medial vs. lateral) differences ( p < 0.05) were found. In varus, STB bone volume fraction (BV/TV) was consistently high throughout the medial condyle, whereas in non-varus, medially, it was more heterogeneously distributed. Regions of high SBP thickness were co-located with regions of high STB BV/TV underneath. In varus, BV/TV was significantly higher medially than laterally, however, not so in non-varus. Moreover, region-specific significant associations between the SBP thickness and SBP porosity and the underlying STB microarchitecture were detected, which in general were not captured when considering the values averaged for each condyle. As subchondral bone changes reflect responses to local mechanical and biochemical factors within the joint, our results suggest that joint alignment influences both the medial-to-lateral and the within-condyle distribution of force across the tibia, generating corresponding local bony responses (adaptation) of both the subchondral bone plate and underlying subchondral trabecular bone microarchitecture. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1927-1941, 2017. [ABSTRACT FROM AUTHOR]

Digital volume correlation (DVC) provides experimental measurements of displacements and strains throughout the interior of porous materials such as trabecular bone. It can provide full-field continuum-and tissue-level measurements, desirable for validation of finite element models, by comparing image volumes from subsequent mCT scans of a sample in unloaded and loaded states. Since the first application of DVC for measurement of strain in bone tissue, subsequent reports of its application to trabecular bone cores up to whole bones have appeared within the literature. An "optimal" set of procedures capable of precise and accurate measurements of strain, however, still remains unclear, and a systematic review focussing explicitly on the increasing number of DVC algorithms applied to bone or structurally similar materials is currently unavailable. This review investigates the effects of individual parameters reported within individual studies, allowing to make recommendations for suggesting algorithms capable of achieving high accuracy and precision in displacement and strain measurements. These recommendations suggest use of subsets that are sufficiently large to encompass unique datasets (e.g. subsets of 500 mm edge length when applied to human trabecular bone cores, such as cores 10 mm in height and 5 mm in diameter, scanned at 15 mm voxel size), a shape function that uses full affine transformations (translation, rotation, normal strain and shear strain), the robust normalized cross-correlation coefficient objective function, and high-order interpolation schemes. As these employ computationally burdensome algorithms, researchers need to determine whether they have the necessary computational resources or time to adopt such strategies. As each algorithm is suitable for parallel programming however, the adoption of high precision techniques may become more prevalent in the future. [ABSTRACT FROM AUTHOR]