Age-related regional deterioration patterns and changes in nanoscale characterizations of trabeculae in the femoral head

Quantitative Analysis of Primary Compressive Trabeculae Distribution in the Proximal Femur of the Elderly

OBJECTIVE

As osteoporosis progresses, the primary compressive trabeculae (PCT) in the proximal femur remains preserved and is deemed the principal load-bearing structure that links the femoral head with the femoral neck. This study aims to elucidate the distribution patterns of PCT within the proximal femur in the elderly population, and to assess its implications for the development and optimization of internal fixation devices used in hip fracture surgeries.

METHODS

This is a retrospective cohort study conducted from March 2022 to April 2023. A total of 125 patients who underwent bilateral hip joint CT scans in our hospital were enrolled. CT data of the unaffected side of the hip were analyzed. Key parameters regarding the PCT distribution in the proximal femur were measured, including the femoral head's radius (R), the neck-shaft angle (NSA), the angle between the PCT-axis and the head-neck axis (α), the distance from the femoral head center to the PCT-axis (δ), and the lengths of the PCT's bottom and top boundaries (L-bottom and L-top respectively). The impact of gender differences on PCT distribution patterns was also investigated. Student's t-test or Mann-Whitney U test were used to compare continuous variables between genders. The relationship between various variables was investigated through Pearson's correlation analysis.

RESULTS

PCT was the most prominent bone structure within the femoral head. The average NSA, α, and δ were 126.85 ± 5.85°, 37.33 ± 4.23°, and 0.39 ± 1.22 mm, respectively, showing no significant gender differences (p > 0.05). Pearson's correlation analysis revealed strong correlations between α and NSA (r = -0.689, p < 0.001), and R and L-top (r = 0.623, p < 0.001), with mild correlations observed between δ and NSA (r = -0.487, p < 0.001), and R and L-bottom (r = 0.427, p < 0.001). Importantly, our study establishes a method to accurately localize PCT distribution in true anteroposterior (AP) radiographs of the hip joint, facilitating precise screw placement in proximal femur fixation procedures.

CONCLUSION

Our study provided unprecedented insights into the distribution patterns of PCT in the proximal femur of the elderly population. The distribution of PCT in the proximal femur is predominantly influenced by anatomical and geometric factors, such as NSA and femoral head size, rather than demographic factors like gender. These insights have crucial implications for the design of internal fixation devices and surgical planning, offering objective guidance for the placement of screws in hip fracture treatments.

Morphologic and mechanical adaptive variations in Saiga tatarica calcaneus: A model for interpreting the bone functional adaptation of wild artiodactyl in captivity

Background and Aim

Captivity alters the locomotor behavior of wild artiodactyls and affects the mechanical loading of the calcaneus; however, the resulting adaptive changes in calcaneus morphology have not been sufficiently studied to date. This study aimed to investigate the morphological and mechanical adaptive variations in the calcaneus of Saiga tatarica to understand further the functional adaptation of the calcaneus in wild artiodactyl to captivity.

Materials and Methods

Paired calcanei from autopsy samples of six captive wild artiodactyls (S. tatarica) and six domesticated artiodactyls (Ovis aries) were divided into skeletally immature and mature groups using X-ray evaluation of growth plate closure. High-resolution microcomputed tomography revealed a calcaneal diaphyseal cross-section. The mechanical and nanomorphological characteristics of the trabecular bone were determined by atomic force microscopy.

Results

The percent cortical bone area (%CA), cortical thickness ratio (CTR), and Young's modulus (E) differed between species in the immature groups but not in the mature groups. S. tatarica had significantly higher growth rates for %CA, CTR, and E in the mid-shaft than O. aries (p < 0.05).

Conclusion

The calcaneus morphology of S. tatarica converges with that of domesticated O. aries during ontogeny. These results indicate that the calcaneus of wild artiodactyls can undergo potentially transitional changes during the short-term adaptation to captivity. The above parameters can be preliminarily identified as morphological signs of functional bone adaptation in artiodactyls.

Femoral neck system versus multiple cannulated screws for the fixation of Pauwels classification type II femoral neck fractures in older female patients with low bone mass

BACKGROUND

Femoral neck fractures in older adult patients are a major concern and often necessitate surgical intervention. This study compared the clinical outcomes of 2 surgical techniques: the femoral neck system (FNS) and cannulated compression screws (CCSs).

METHODS

A total of 40 female patients (mean age 73.50 ± 11.55 years) with femoral neck fractures of Pauwels classification type II and receiving surgical fixation between 2020 and 2022 were enrolled. The patients were categorized into an FNS group (n = 12) or a CCS group (n = 28), and surgical duration, intraoperative blood loss, length of hospital stay, and incidence of postoperative adverse events were analyzed.

RESULTS

No significant intergroup differences in demographic characteristics were discovered. The mean surgical duration for all patients was 52.88 ± 22.19 min, with no significant difference between the groups. However, the FNS group experienced significantly higher intraoperative blood loss (P = 0.002) and longer hospital stay (P = 0.023) than did the CCS group. The incidence of osteonecrosis was higher in the CCS group, whereas the incidence of nonunion or malunion was higher in the FNS group. The surgical method did not appear to be a significant risk factor. The main risk factor for revision surgery was longer duration until the first adverse event (P = 0.015).

CONCLUSION

The FNS does not appear to provide superior surgical outcomes compared with CCSs in older adult women with Pauwels classification type II femoral neck fractures. A longer duration between surgical fixation and the first adverse event before stabilization of the fracture site may be a risk factor for revision surgery.

Incremental Element Deletion-Based Finite Element Analysis of the Effects of Impact Speeds, Fall Postures, and Cortical Thicknesses on Femur Fracture

The proximal femur’s numerical simulation could give an effective method for predicting the risk of femoral fracture. However, the majority of existing numerical simulations is static, which does not correctly capture the dynamic properties of bone fractures. On the basis of femoral fracture analysis, a dynamic simulation using incremental element deletion (IED)-based finite element analysis (FEA) was developed and compared to XFEM in this study. Mechanical tests were also used to assess it. Different impact speeds, fall postures, and cortical thicknesses were also studied for their implications on fracture types and mechanical responses. The time it took for the crack to shatter was shorter when the speed was higher, and the crack line slid down significantly. The fracture load fell by 27.37% when the angle was altered from 15° to 135°, indicating that falling forward was less likely to cause proximal femoral fracture than falling backward. Furthermore, the model with scant cortical bone was susceptible to fracture. This study established a theoretical foundation and mechanism for forecasting the risk of proximal femoral fracture in the elderly.

Strain Distribution Evaluation of Rat Tibia under Axial Compressive Load by Combining Strain Gauge Measurement and Finite Element Analysis

This study is aimed at providing an effective method for determining strain-load relationship and at quantifying the strain distribution within the whole tibia under axial compressive load on rats. Rat tibial models with axial compressive load were designed. Strains in three directions (0°, 45°, and 90°) at the proximal shaft of the tibia were measured by using a strain gauge rosette, which was used to calculate the maximum and minimum principal strains. Moreover, the strain at the midshaft of the tibia was measured by a single-element strain gauge. The slopes of the strain-load curves with different peak loads were calculated to assess the stability of the strain gauge measurement. Mechanical environment in the whole tibia by the axial compressive load was quantified using finite element analysis (FEA) based on microcomputed tomography images. The von Mises elastic strain distributions of the whole tibiae were evaluated. Slopes of the strain-load curves showed no significant differences among different peak loads (ANOVA; P > 0.05), indicating that the strain-load relationship obtained from the strain gauge measurement was reasonable and stable. The FEA results corresponded to the experimental results with an error smaller than 15% (paired Student's t-test, P > 0.05), signifying that the FEA can simulate the experiment reasonably. FEA results showed that the von Mises elastic strain was the lowest in the middle and gradually increased to both sides along the lateral direction, with the maximal von Mises elastic strain being observed on the posterior side under the distal tibiofibular synostosis. The method of strain gauge measurements and FEA used in this study can provide a feasible way to obtain the mechanical environment of the tibiae under axial compressive load on the rats and serve as a reference for further exploring the mechanical response of the bone by axial compressive load.

A cross-sectional study on the age-related cortical and trabecular bone changes at the femoral head in elderly female hip fracture patients

Bone is in a continuous state of remodeling whereby old bone is absorbed and new bone is formed in its place. During this process, new formations reinforce the bone in the direction of the dominant stress trajectories through a functional adaptation. In normal aging, the balance between bone resorption and formation can be shifted. How this affects the functional adaptation remains to be investigated. Furthermore, how or whether the bone continues to change beyond the age of 85 is not yet studied in detail. In this study we examined the age-related changes in the cortical and trabecular bone in old age, and assessed whether we can find evidence of the presence of functional adaptation. We measured cortical and trabecular parameters from micro-computed tomography scans of the femoral head extracted from hip fracture patients between the age of 70 and 93 years. A significant decrease in global trabecular bone mineral density (38.1%) and cortical thickness (13.0%) was seen from the 9th to the 10th decade of life. The degree of anisotropy was maintained globally as well as locally in both high and low stress regions. The local trabecular bone mineral density decreased in both high stress and low stress regions between the 9th and 10th decade of life with similar trends. This suggests that the role of functional adaptation in maintaining the bone structural integrity in old age may be limited. This study highlights the need for a controlled clinical trial examining the cause of the continued bone degradation throughout old age.

Measuring bone stiffness using spherical indentation

Objectives

Bone material properties are a major determinant of bone health in older age, both in terms of fracture risk and implant fixation, in orthopaedics and dentistry. Bone is an anisotropic and hierarchical material so its measured material properties depend upon the scale of metric used. The scale used should reflect the clinical problem, whether it is fracture risk, a whole bone problem, or implant stability, at the millimetre-scale. Indentation, an engineering technique involving pressing a hard-tipped material into another material with a known force, may be able to assess bone stiffness at the millimetre-scale (the apparent elastic modulus). We aimed to investigate whether spherical-tip indentation could reliably measure the apparent elastic modulus of human cortical bone.

Materials and methods

Cortical bone samples were retrieved from the femoral necks of nineteen patients undergoing total hip replacement surgery (10 females, 9 males, mean age: 69 years). The samples underwent indentation using a 1.5 mm diameter, ruby, spherical indenter tip, with sixty indentations per patient sample, across six locations on the bone surfaces, with ten repeated indentations at each of the six locations. The samples then underwent mechanical compression testing. The repeatability of indentation measurements of elastic modulus was assessed using the co-efficient of repeatability and the correlation between the bone elastic modulus measured by indentation and compression testing was analysed by least-squares regression.

Results

In total, 1140 indentations in total were performed. Indentation was found to be repeatable for indentations performed at the same locations on the bone samples with a mean co-efficient of repeatability of 0.4 GigaPascals (GPa), confidence interval (C.I): 0.33–0.42 GPa. There was variation in the indentation modulus results between different locations on the bone samples (mean co-efficient of repeatability: 3.1 GPa, C.I: 2.2–3.90 GPa). No clear correlation was observed between indentation and compression values of bone elastic modulus (r = 0.33, p = 0.17). The mean apparent elastic modulus obtained by spherical indentation was 9.9 GPa, the standard deviation for each indent cycle was 0.11 GPa, and the standard deviation between locations on the same sample was 1.01 GPa. The mean compression apparent elastic modulus was 4.42 GPa, standard deviation 1.02 GPa.

Discussion

Spherical-tip indentation was found to be a repeatable test for measuring the elastic modulus of human cortical bone, demonstrated by a low co-efficient of repeatability in this study. It could not, however, reliably predict cortical bone elastic modulus determined by platens compression testing in this study. This may be due to indentation only probing mechanical properties at the micro-scale while platens compression testing assesses millimetre length-scale properties. Improvements to the testing technique, including the use of a larger diameter spherical indenter tip, may improve the measurement of bone stiffness at the millimetre scale and should be investigated further.

Tissue-Level Mechanical Properties of Bone Contributing to Fracture Risk

Tissue-level mechanical properties characterize mechanical behavior independently of microscopic porosity. Specifically, quasi-static nanoindentation provides measurements of modulus (stiffness) and hardness (resistance to yielding) of tissue at the length scale of the lamella, while dynamic nanoindentation assesses time-dependent behavior in the form of storage modulus (stiffness), loss modulus (dampening), and loss factor (ratio of the two). While these properties are useful in establishing how a gene, signaling pathway, or disease of interest affects bone tissue, they generally do not vary with aging after skeletal maturation or with osteoporosis. Heterogeneity in tissue-level mechanical properties or in compositional properties may contribute to fracture risk, but a consensus on whether the contribution is negative or positive has not emerged. In vivo indentation of bone tissue is now possible, and the mechanical resistance to microindentation has the potential for improving fracture risk assessment, though determinants are currently unknown.

Modeling the Mechanical Consequences of Age-Related Trabecular Bone Loss by XFEM Simulation

The elderly are more likely to suffer from fracture because of age-related trabecular bone loss. Different bone loss locations and patterns have different effects on bone mechanical properties. Extended finite element method (XFEM) can simulate fracture process and was suited to investigate the effects of bone loss on trabecular bone. Age-related bone loss is indicated by trabecular thinning and loss and may occur at low-strain locations or other random sites. Accordingly, several ideal normal and aged trabecular bone models were created based on different bone loss locations and patterns; then, fracture processes from crack initiation to complete failure of these models were observed by XFEM; finally, the effects of different locations and patterns on trabecular bone were compared. Results indicated that bone loss occurring at low-strain locations was more detrimental to trabecular bone than that occurring at other random sites; meanwhile, the decrease in bone strength caused by trabecular loss was higher than that caused by trabecular thinning, and the effects of vertical trabecular loss on mechanical properties were more severe than horizontal trabecular loss. This study provided a numerical method to simulate trabecular bone fracture and distinguished different effects of the possible occurrence of bone loss locations and patterns on trabecular bone.

Quantification of Age-Related Tissue-Level Failure Strains of Rat Femoral Cortical Bones Using an Approach Combining Macrocompressive Test and Microfinite Element Analysis

Bone mechanical properties vary with age; meanwhile, a close relationship exists among bone mechanical properties at different levels. Therefore, conducting multilevel analyses for bone structures with different ages are necessary to elucidate the effects of aging on bone mechanical properties at different levels. In this study, an approach that combined microfinite element (micro-FE) analysis and macrocompressive test was established to simulate the failure of male rat femoral cortical bone. Micro-FE analyses were primarily performed for rat cortical bones with different ages to simulate their failure processes under compressive load. Tissue-level failure strains in tension and compression of these cortical bones were then back-calculated by fitting the experimental stress–strain curves. Thus, tissue-level failure strains of rat femoral cortical bones with different ages were quantified. The tissue-level failure strain exhibited a biphasic behavior with age: in the period of skeletal maturity (1–7 months of age), the failure strain gradually increased; when the rat exceeded 7 months of age, the failure strain sharply decreased. In the period of skeletal maturity, both the macro- and tissue-levels mechanical properties showed a large promotion. In the period of skeletal aging (9–15 months of age), the tissue-level mechanical properties sharply deteriorated; however, the macromechanical properties only slightly deteriorated. The age-related changes in tissue-level failure strain were revealed through the analysis of male rat femoral cortical bones with different ages, which provided a theoretical basis to understand the relationship between rat cortical bone mechanical properties at macro- and tissue-levels and decrease of bone strength with age.