Effects of processing and gamma radiation on mechanical properties and organic composition of frozen, freeze-dried and demineralised human cortical bone allograft.

Bone processing and radiation were reported to influence mechanical properties of cortical bones due in part to structural changes and denaturation of collagen composition. This comparative study was to determine effects of bone processing on mechanical properties and organic composition, and to what extent the radiation damaging after each processing. Human femur cortical bones were processed by freezing, freeze-drying and demineralisation and then gamma irradiated at 5, 15, 20, 25 and 50 kGy. In the compression test, freeze drying significantly decreased the Young's Modulus by 15%, while demineralisation reduced further by 90% (P < 0.05) when compared to the freezing. Only demineralisation significantly reduced ultimate strength of bone by 93% (P < 0.05). In the bending test, both freeze drying and demineralisation significantly reduced the ultimate strength and the work to failure. Radiation at 25 kGy showed no effect on compression for ultimate strength in each processing group. However, high dose of 50 kGy significantly reduced bending ultimate strength by 47% in demineralisation group. Alterations in collagen in bones irradiated at 25 and 50 kGy showed by the highest peak of the amide I collagen in the Fourier Transfer Infra-Red spectra indicating more collagen was exposed after calcium was removed in the demineralised bone, however radiation showed no effect on the collagen crosslink. The study confirmed that demineralisation further reduced the ability to resist deformation in response to an applied force in freeze-dried bones due to calcium reduction and collagen composition. Sterilisation dose of 25 kGy has no effect on mechanical properties and collagen composition of the processed human cortical bone.

Three-dimensional morphometric study of the trapezium shape of the trochlea tali.

The trapezium shape of the talar dome limits the use of 2-dimensional plain radiography for morphometric assessment because only 2 of the 4 required parameters can be measured. We used computed tomography data to measure the 4 morphologic parameters of the trochlea tali: anterior width, posterior width, trochlea tali length, and angle of trapezium shape. A total of 99 subjects underwent computed tomography scanning, and the left and right talus bones were both virtually modeled in 3 dimensions. The 4 morphologic parameters were measured 3 times each to obtain the intraclass correlation, and analysis of variance was used to check for any significant differences between the repeated measurements. The average intraclass correlation coefficient for the measurements for 2 to 3 trials was 0.94 ± 0.04. Statistical analyses were performed on the data from all 198 talus bones using SAS software, comparing male and female and left and right bones. All 4 morphometric values were greater in the male group. No significant differences were found between the left and right talus bones. A strong positive correlation was observed between the trochlea tali length and the anterior width. The angle of trapezium shape showed no correlation with the other 3 parameters. The measurements were compared with the dimensions of the current talar components of 4 total ankle arthroplasty implants. However, most of them did not perfectly match the trapezium shape of the talus from our population. We successfully analyzed the trapezium shape of the trochlea tali using reliable virtual 3-dimensional measurements. Compared with other published reports, our study showed a relatively smaller dimension of the trochlea tali than the European counterparts.

Effects of conform, non-conform, and hybrid conformity toward stress distribution at the glenoid implant and cement: A finite element study.

Glenoid conformity is one of the important aspects that could contribute to implant stability. However, the optimal conformity is still being debated among the researchers. Therefore, this study aims to analyze the stress distribution of the implant and cement in three types of conformity (conform, non-conform, and hybrid) in three load conditions (central, anterior, and posterior). Glenoid implant and cement were reconstructed using Solidwork software and a 3D model of scapula bone was done using MIMICS software. Constant load, 750 N, was applied at the central, anterior, and posterior region of the glenoid implant which represents average load for daily living activities for elder people, including, walking with a stick and standing up from a chair. The results showed that, during center load, an implant with dual conformity (hybrid) showed the best (Max Stress-3.93 MPa) and well-distributed stress as compared to other conformity (Non-conform-7.21 MPa, Conform-9.38 MPa). While, during eccentric load (anterior and posterior), high stress was located at the anterior and posterior region with respect to the load applied. Cement stress for non-conform and hybrid implant recorded less than 5 MPa, which indicates it had a very low risk to have cement microcracks, whilst, conform implant was exposed to microcrack of the cement. In conclusion, hybrid conformity showed a promising result that could compromise between conform and non-conform implant. However, further enhancement is required for hybrid implants when dealing with eccentric load (anterior and posterior).

Fluid-structure interaction (FSI) modeling of bone marrow through trabecular bone structure under compression.

The present study has sought to investigate the fluid characteristic and mechanical properties of trabecular bone using fluid-structure interaction (FSI) approach under different trabecular bone orientations. This method imposed on trabecular bone structure at both longitudinal and transverse orientations to identify effects on shear stress, permeability, stiffness and stress regarded to the trabeculae. Sixteen FSI models were performed on different range trabecular cubes of 27 mm3 with eight models developed for each longitudinal and transverse direction. Results show that there was a moderate correlation between permeability and porosity, and surface area in the longitudinal and transverse orientations. For the longitudinal orientation, the permeability values varied between 3.66 × 10-8 and 1.9 × 10-7 and the sheer stress values varied between 0.05 and 1.8 Pa, whilst for the transverse orientation, the permeability values varied between 5.95 × 10-10 and 1.78 × 10-8 and the shear stress values varied between 0.04 and 3.1 Pa. Here, transverse orientation limits the fluid flow from passing through the trabeculae due to high shear stress disturbance generated within the trabecular bone region. Compared to physiological loading direction (longitudinal orientation), permeability is higher within the range known to trigger a response in bone cells. Additionally, shear stresses also increase with bone surface area. This study suggests the shear stress within bone marrow in real trabecular architecture could provide the mechanical signal to marrow cells that leads to bone anabolism and can depend on trabecular orientation.

Impacts of dynamic degradation on the morphological and mechanical characterisation of porous magnesium scaffold.

This study employs a computational approach to analyse the impact of morphological changes on the structural properties of biodegradable porous Mg subjected to a dynamic immersion test for its application as a bone scaffold. Porous Mg was immersed in a dynamic immersion test for 24, 48, and 72 h. Twelve specimens were prepared and scanned using micro-CT and then reconstructed into a 3D model for finite element analysis. The structural properties from the numerical simulation were then compared to the experimental values. Correlations between morphological parameters, structural properties, and fracture type were then made. The relative losses were observed to be in agreement with relative mass loss done experimentally. The degradation rates determined using exact (degraded) surface area at particular immersion times were on average 20% higher than the degradation rates obtained using original surface area. The dynamic degradation has significantly impacted the morphological changes of porous Mg in volume fraction, surface area, and trabecular separation, which in turn affects its structural properties and increases the immersion time.