Reduced cortical bone thickness increases stress and strain in the female femoral diaphysis analyzed by a CT-based finite element method: Implications for the anatomical background of fatigue fracture of the femur

The cross-sectional morphology of the proximal femoral diaphysis is defined by the anteversion angle

Osteoporosis in postmenopausal women is one of the causes of femoral fractures and is prevented by the administration of bisphosphonates. Individual morphologies are considered to increase the risk of atypical fractures associated with long-term administration. To evaluate cortical bone morphology quantitatively, we established a method to measure the distance from the center point of a cross-section to the external and internal borders based on CT images. Using this method, 44 sides of a female femoral skeleton specimen were examined and areas of protrusion and thickening in the medial anterior and lateral posterior regions just below the lesser trochanter were identified. These positions strongly correlated with the anteversion angle, suggesting the involvement of the distribution of the load received from body weight defined by the angle. The finite element method was used to examine the relationships between the positions of these areas with compressive and tensile stress distribution areas in the one-legged standing condition. The medial anterior region and lateral posterior region protruded and thickened in response to compressive and tensile stress, respectively. In addition, a hierarchical relationship was observed between the anteversion angle, tensile stress distribution, protrusion, and thickening in femurs with thinning of cortical bone, indicating that morphogenesis occurs adaptively to loading. The present results demonstrate the usefulness of this method in considering the formation mechanism and function of the femoral diaphysis and suggest that bone remodeling is necessary to maintain adaptability.

Osteon shape variation in the femoral diaphysis: A geometric-morphometric approach on human cortical bone microstructure in an elderly sample

Geometric morphometrics (GMM) have been applied to understand morphological variation in biological structures. However, research studying cortical bone through geometric histomorphometrics (GHMM) is scarce. This research aims to develop a landmark-based GHMM protocol to depict osteonal shape variation in the femoral diaphysis, exploring the role of age and biomechanics in bone microstructure. Proximal, midshaft, and distal anatomical segments from the femoral diaphysis of six individuals were assessed, with 864 secondary intact osteons from eight periosteal sampling areas being manually landmarked. Observer error was tested using Procrustes ANOVA. Average osteonal shape and anatomical segment-specific variation were explored using principal component analysis. Osteon shape differences between segments were examined using canonical variate analysis (CVA). Sex differences were assessed through Procrustes ANOVA and discriminant function analysis (DFA). The impact of osteonal size on osteonal shape was investigated. High repeatability and reproducibility in osteon shape landmarking were reported. The average osteon shape captured was an elliptical structure, with PC1 reflecting more circular osteons. Significant differences in osteon shape were observed between proximal and distal segments according to CVA. Osteon shape differed between males and females, with DFA showing 52% cross-validation accuracies. No effect of size on shape was reported. Osteonal shape variation observed in this study might be explained by the elderly nature of the sample as well as biomechanical and physiological mechanisms playing different roles along the femoral diaphysis. Although a larger sample is needed to corroborate these findings, this study contributes to the best of our knowledge on human microanatomy, proposing a novel GHMM approach.

Ex vivo analysis of cortical microarchitecture of the distal clavicle: implications for surgical management of fractures

BACKGROUND

Cortical thickness and porosity are two main determinants of cortical bone strength. Thus, mapping variations in these parameters across the full width of the distal end of the clavicle may be helpful for better understanding the basis of distal clavicle fractures and for selecting optimal surgical treatment.

METHODS

Distal ends of 11 clavicles (6 men, 5 women; age: 81.9 ± 15.1 years) were scanned by micro-computed tomography at 10-µm resolution. We first analyzed cortical thickness and porosity of each 500-μm-wide area across the superior surface of distal clavicle at the level of conoid tubercle in an antero-posterior direction. This level was chosen for detailed evaluation because previous studies have demonstrated its superior microarchitecture relative to the rest of the distal clavicle. Subsequently, we divided the full width of distal clavicle to three subregions (anterior, middle, and posterior) and analyzed cortical porosity, pore diameter, pore separation, and cortical thickness.

RESULTS

We found the largest number of low-thickness and high-porosity areas in the anterior subregion. Cortical porosity, pore diameter, pore separation, and cortical thickness varied significantly among the three subregions (p < 0.001 p = 0.016, p = 0.001, p < 0.001, respectively). Cortex of the anterior subregion was more porous than that of the middle subregion (p < 0.001) and more porous and thinner than that of the posterior subregion (p < 0.001, p = 0.030, respectively). Interaction of site and sex revealed higher porosity of the anterior subregion in women (p < 0.001). The anterior subregion had larger pores than the middle subregion (p = 0.019), whereas the middle subregion had greater pore separation compared with the anterior (p = 0.002) and posterior subregions (p = 0.006). In general, compared with men, women had thinner (p < 0.001) and more porous cortex (p = 0.03) with larger cortical pores (p < 0.001).

CONCLUSIONS

Due to high cortical porosity and low thickness, the anterior conoid subregion exhibits poor bone microarchitecture, particularly in women, which may be considered in clinical practice.

LEVELS OF EVIDENCE

Level IV.

Stress reduction through cortical bone thickening improves bone mechanical behavior in adult female Beclin-1+/- mice

Fragility fractures, which are more prevalent in women, may be significantly influenced by autophagy due to altered bone turnover. As an essential mediator of autophagy, Beclin-1 modulates bone homeostasis by regulating osteoclast and chondrocyte differentiation, however, the alteration in the local bone mechanical environment in female Beclin-1+/- mice remains unclear. In this study, our aim is to investigate the biomechanical behavior of femurs from seven-month-old female wild-type (WT) and Beclin-1+/- mice under peak physiological load, using finite element analysis on micro-CT images. Micro-CT imaging analyses revealed femoral cortical thickening in Beclin-1+/- female mice compared to WT. Three-point bending test demonstrated a 63.94% increase in whole-bone strength and a 61.18% increase in stiffness for female Beclin-1+/- murine femurs, indicating improved biomechanical integrity. After conducting finite element analysis, Beclin-1+/- mice exhibited a 26.99% reduction in von Mises stress and a 31.62% reduction in maximum principal strain in the femoral midshaft, as well as a 36.64% decrease of von Mises stress in the distal femurs, compared to WT mice. Subsequently, the strength-safety factor was determined using an empirical formula, revealing that Beclin-1+/- mice exhibited significantly higher minimum safety factors in both the midshaft and distal regions compared to WT mice. In summary, considering the increased response of bone adaptation to mechanical loading in female Beclin-1+/- mice, our findings indicate that increasing cortical bone thickness significantly improves bone biomechanical behavior by effectively reducing stress and strain within the femoral shaft.

Thinner femoral cortical thickness in patients with destructive rheumatoid arthritis of the knee

BACKGROUND

The examination of femoral cortical bone thickness in patients with rheumatoid arthritis (RA) has been notably limited in prior research. We aimed to compare femoral cortical thickness in patients with rheumatoid arthritis (RA) and healthy controls and to investigate the association between femoral cortical thickness and clinical parameters within the RA group.

METHODS

Forty-four patients (58 limbs) with RA who underwent total knee arthroplasty were enrolled. Preoperative computed tomography images of the lower limbs were analyzed. The femoral cortex was divided into the proximal, central, and distal diaphysis regions and further into the anterior, posterior, medial, and lateral regions. The divisions were measured using Stradwin® software and standardized by femoral length. Femoral cortical thickness was compared between RA and healthy control (n = 25) groups. Correlation analyses between standardized cortical thickness and disease parameters were performed in the RA group.

RESULTS

The RA group had significantly lower standardized femoral cortical thickness at the anterior and medial distal diaphysis than healthy controls. Standardized proximal lateral and central lateral in the RA group were significantly larger than those in the healthy control groups. Standardized femoral cortical thickness was significantly correlated with bone mineral density (BMD) in 11 areas, except the posterior central diaphysis, and with body mass index in 8 areas, except the central posterior, distal lateral, distal anterior, and distal medial diaphysis.

CONCLUSIONS

Femoral cortical thinning was noted in patients with RA complicated with destructive knee, particularly at the anterior and medial distal diaphysis. Femoral cortical thickness was significantly correlated with BMD and body mass index (BMI); thus, patients with RA and low BMD and BMI should be cared for to prevent fragility fractures.

Changes in tibial cortical dimensions and density associated with long-term locking plate fixation in goats

PURPOSE

Cortical porosis, secondary to either vascular injury or stress-shielding, is a comorbidity of fracture fixation using compression bone plating. Locking plate constructs have unique mechanics of load transmission and lack of reliance on contact pressures for fixation stability, so secondary cortical porosis adjacent to the plate has not been widely investigated. Therefore, this study aimed to assess the effects of long-term locking plate fixation on cortical dimensions and density in a caprine tibial segmental ostectomy model.

METHODS

Data was acquired from a population of goats enrolled in ongoing orthopedic research which utilized locking plate fixation of 2 cm tibial diaphyseal segmental defects to evaluate bone healing over periods of 3, 6, 9, and 12 months. Quantitative data included tibial cortical width measurements and three-dimensionally reconstructed slab density measurements, both assessed using computed tomographic examinations performed at the time of plate removal. Additional surgical and demographic variables were analyzed for effect on cortical widths and density, and all cis-cortex measurements were compared to both the trans-cortex and to the contralateral limbs.

RESULTS

The tibial cis-cortex was significantly wider and more irregular than the trans-cortex at the same level. This width asymmetry differed in both magnitude and direction from the contralateral limb. The bone underlying the plate was significantly less dense than the trans-cortex, and this cortical density difference was significantly greater than that of the contralateral limb. These cortical changes were independent of both duration of fixation and degree of ostectomy bone healing.

CONCLUSIONS

This study provides evidence that cortical bone loss consistent with cortical porosity is a comorbidity of locking plate fixation in a caprine tibial ostectomy model. Further research is necessary to identify risk factors for locking-plate-associated bone loss and to inform clinical decisions in cases necessitating long-term locking plate fixation.

A Scientific Proposal for Surgical Decision-Making in Occult Intertrochanteric Fractures Based on Finite Element Analysis

Background In the treatment of femoral intertrochanteric fractures, there is still a lack of consensus on the optimal approach for isolated greater trochanteric fractures and insufficient intertrochanteric fractures. The limited number of patients and restricted access to accurate assessment of fracture extension using magnetic resonance imaging contribute to the unclear treatment strategy. This study aims to utilize finite element (FE) analysis to analyze stress values at the fracture line and investigate their influence on intertrochanteric fracture extension under different loading conditions. The hypothesis is that fracture extension occurs following certain conditions, supporting the need for surgery based on scientific evidence. Methodology Osseous data from a computed tomography (CT) scan was used to create a proximal femur FE model using FEA software. CT scan data were converted to Digital Imaging and Communications in Medicine format and used to generate the FE model. Trabecular bone and cortex were meshed into tetrahedral elements. The model consisted of 1,592,642 elements and 282,530 nodes. Two models were created, namely, healthy proximal femur (HF) and femoral insufficient intertrochanteric fracture (FIF). Material properties were assigned based on CT values and conversion equations. The distal end of the femur was constrained. Stress analysis using the dynamic explicit approach was performed. Von Mises stresses were calculated for the proximal femur. The number of elements exceeding yield stress was counted to predict fracture risk by focusing on fracture line spots. In this study, the distribution of von Mises stress was compared between the HF and the FIF models. Six loading combinations were considered, namely, two weight-bearing conditions (3 W loading simulating for walking and 1/3 W for touch-down standing) and three hip flexion angles (0°, 15°, and 23°). Results Under 3 W loading, no significant stress elevations were observed in the HF model at any flexion angles. However, the FIF model exhibited increased stress at the site of the posterior fracture line extension. This stress-induced element destruction was observed in both cortical and cancellous bone. For the 1/3 W loading condition, only minimal stress elevation was observed in both HF and FIF models. To assess the influence on fracture extension, the number of yielded elements was evaluated along the fracture line edges (greater trochanter and middle of the intertrochanteric ridge). Under 3 W loading, the HF model had only one yielded element, indicating minimal fracture risk. In contrast, the FIF model exhibited a notable presence of yield elements in various regions (total/greater trochanter/shaft) at different flexion angles: 0° (115/16/28), 15° (265/158/23), and 23° (446/233/34). Under the 1/3 W loading condition, neither the HF nor the FIF models showed any yielding elements, regardless of the direction of external force. Conclusions The results demonstrated elevated stress levels at the fracture line in the FIF model, particularly during walking, indicating a higher risk of fracture extension at the flex position. However, under reduced weight-bearing conditions, the stress at the fracture site remained within the yield stress range, suggesting a relatively low risk of fracture extension. These findings hold significant clinical implications for developing surgical protocols that consider patients' compliance with weight-bearing restrictions.

Modified pedicle screw fixation under guidance of stress analysis for cervicothoracic junction: Surgical technique and outcomes

BACKGROUND

In cervicothoracic junction, the use of strong fixation device such as pedicle screw placement is often needed.

OBJECTIVE

The current study aimed to evaluate the accuracy and safety of pedicle screw placement using stress conduction analysis in the clinical application.

METHODS

We retrospectively collected patients who underwent pedicle screw internal fixation in cervicothoracic junction. Patients were divided into conventional nail placement (Group A) and modified pedicle screw implantation under guidance of stress analysis (Group B) according to the methods of pedicle screw placement. The accuracy of pedicle screw placement was assessed by computed tomography (CT) examination, and the success rate was calculated.

RESULTS

A total of 80 patients who underwent pedicle screw internal fixation in cervicothoracic junction were included. There were no obvious differences in baseline characteristics between two groups. The success rate of total screw placement, cervical spine screw placement and upper thoracic spine screw placement in Group B was higher than those in Group A (P< 0.001, P= 0.005, P= 0.008). Additionally, Heary Grade I in the Group B was higher than Group A (P= 0.001).

CONCLUSION

Stress analysis-guided technique can increase the accuracy of pedicle screw placement. Importantly, it meets the requirements of internal fixation of the cervicothoracic junction.

Cross-sectional geometry of the femoral diaphyseal cortical bones: analysis of central mass distribution

A detailed analysis of differences in skeletal shape among many individuals is expected to reveal the mechanical significance behind various morphological features. To confirm the distribution of the cortical bone region in cross sections, the relative position of the central mass distribution (CMD) of the cortical bone region to the CMD of the entire cross section was examined. A total of 90 right human femoral skeletons were examined using clinical multi-slice computed tomography. For nine cross sections of each femur, we determined the CMD of the whole area, including both cortical bone and medullary areas, as CMD-W, and that of the cortical bone region in the same cross section as CMD-C, and they were compared. The medial and anterior portion of the cortex was relatively thick just below the lesser trochanter. The posterior cortical bone tended to be relatively thick in the region from the center to the distal part of the diaphysis. Females had a significantly more medially deviated CMD than males throughout the entire diaphysis. These results suggest that femurs with advanced cortical bone thinning tend to have a concentration of cortical bone in their medial portion. CMD-C was located farther from the diaphysis axis as the degree of medial bending increased. Conversely, the greater the lateral bending of the diaphysis, the closer CMD-C was to the diaphysis axis. As the amount of bone decreases with age, self-adjustment could occur so that the cortical bone's critical area remains to prevent a decrease in mechanical strength.

Increased Cortical Porosity, Reduced Cortical Thickness, and Reduced Trabecular and Cortical Microhardness of the Superolateral Femoral Neck Confer the Increased Hip Fracture Risk in Individuals with Type 2 Diabetes

Individuals with diabetes mellitus type 2 (T2DM) have approximately 30% increased risk of hip fracture; however, the main cause of the elevated fracture risk in those subjects remains unclear. Moreover, micromechanical and microarchitectural properties of the superolateral femoral neck-the common fracture-initiating site-are still unknown. We collected proximal femora of 16 men (eight with T2DM and eight controls; age: 61 ± 10 years) at autopsy. After performing post-mortem bone densitometry (DXA), the superolateral neck was excised and scanned with microcomputed tomography (microCT). We also conducted Vickers microindentation testing. T2DM and control subjects did not differ in age (p = 0.605), body mass index (p = 0.114), and femoral neck bone mineral density (BMD) (p = 0.841). Cortical porosity (Ct.Po) was higher and cortical thickness (Ct.Th) was lower in T2DM (p = 0.044, p = 0.007, respectively). Of trabecular microarchitectural parameters, only structure model index (p = 0.022) was significantly different between T2DM subjects and controls. Control group showed higher cortical (p = 0.002) and trabecular bone microhardness (p = 0.005). Increased Ct.Po and decreased Ct.Th in T2DM subjects increase the propensity to femoral neck fracture. Apart from the deteriorated cortical microarchitecture, decreased cortical and trabecular microhardness suggests altered bone composition of the superolateral femoral neck cortex and trabeculae in T2DM. Significantly deteriorated cortical microarchitecture of the superolateral femoral neck is not recognized by standard DXA measurement of the femoral neck.

Triangular Mechanical Structure of the Proximal Femur

Objective

The mechanical high modulus structure of the proximal femur could guide clinical surgical treatment and instrument design of proximal femoral fractures. The purpose of this study is to analyze and verify the mechanical structure of the proximal femur.

Methods

A total of 375 patients with intertrochanteric fractures were imaged using computed tomography (CT) scans. Patients were grouped according to age and sex. Cortical and medullary cavity parameters (cortical thickness [CTh], cortical mean density [CM], upper‐lower diameter length [ULL], and medial‐lateral diameter length [MLL]) were measured at eight planes. Six proximal femoral finite element models of different sexes and ages were constructed. To verify the measurement results, Abaqus was used to implement the force load to describe the von Mises stress distribution, and the maximum von Mises stress values of each wall of the proximal femur were compared.

Results

The CTh values of the lower and upper walls were higher than those of the anterior and posterior walls of the femoral neck (p < 0.05). The CM values of the lower and upper walls were higher than those of the anterior and posterior walls of the subcephalic and middle femoral neck (p < 0.05). The ULL value gradually increased from the subcephalic region to the bottom (p < 0.05). The CTh and CM values of the medial and lateral walls were higher than those of the anterior and posterior walls in the femoral trochanteric region (p < 0.05). The MLL value decreased gradually from the plane 20 mm above the upper edge to that 20 mm below the vertex of the femoral lesser trochanter (p < 0.05). The von Mises stress was concentrated on the upper and lower walls of the femoral neck and on the medial and lateral walls of the femoral trochanteric region. The maximum von Mises stress values of the upper and lower walls were higher than those of the anterior and posterior walls of the femoral neck. The maximum von Mises stress values of the medial and lateral walls were higher than those of the anterior and posterior walls in the femoral trochanteric region, except for the plane 20 mm above the upper edge of the femoral lesser trochanter.

Conclusion

The bone mass of the proximal femur presented a triangular high‐modulus distribution, which bore the main stress of the proximal femur. The triangular mechanical structure provides a guideline for the surgical strategy and instrument design of the proximal femur.

Biomechanical Characteristics of the Femoral Isthmus during Total Hip Arthroplasty in Patients with Adult Osteoporosis and Developmental Dysplasia of the Hip: A Finite Element Analysis

Objective

This study investigated the underlying mechanisms of high fracture incidence in the femoral isthmus from a biomechanical perspective.

Methods

We retrospectively analyzed a total of 923 primary total hip arthroplasty (THA) patients and 355 osteoporosis (OP) patients admitted from January 2010 to January 2018. Through a series of screening conditions, 47 patients from each group were selected for inclusion in the study. The datasets on the unaffected side and affected side of the patients with unilateral developmental dysplasia of the hip (uDDH) were respectively classified as the normal group (Group I) and he tDDH group (Group II), and that of patients with osteoporosis were classified as the OP group (Group III). In this study, first, we collected computed tomography (CT) images and measured geometric parameters (inner and outer diameters) of the isthmus. Thereafter, to study biomechanical properties, we established six finite element models and calculated values of von Mises stress for each group with the methods of data conversion and grid processing.

Results

Compared with those of patients in the normal group, the values of the inner and outer diameters of femoral isthmus of patients in the DDH group were significantly lower (P < 0.001), while the inner diameters of patients in the OP group were significantly higher (P < 0.001) and the outer diameters of patients in the OP group showed no significant difference (P> 0.05). The cortical rates of patients in the normal group and the DDH group appeared insignificant (P > 0.05), and those of patients in normal group were significantly higher than those of patients in the OP group (P < 0.001). Moreover, patients in the DDH group showed a higher von Mises stress value than patients in the normal group (P < 0.001), but statistically speaking the values between patients in the OP and normal groups were insignificant (P > 0.05).

Conclusions

The relatively shorter inner and outer diameters of the isthmus in DDH resulted in intensive von Mises stress under the torque of the hip location, and induced a high fracture incidence. However, in patients in the OP group, the geometric morphology exhibited no anatomical variation, and the fracture was not due to the intensity of von Mises stress.

Application of Methods for a Morphological Analysis of the Femoral Diaphysis Based on Clinical CT Images to Prehistoric Human Bone: Comparison of Modern Japanese and Jomon Populations from Hegi Cave, Oita, Japan

A morphological analysis of ancient human bones is essential for understanding life history, medical history, and genetic characteristics. In addition to external measurements, a three-dimensional structural analysis using CT will provide more detailed information. The present study examined adult male human skeletons excavated from Hegi cave, Nakatsu city, Oita Prefecture. CT images were taken from the femurs of adult males (Initial/Early Jomon Period (n = 10) and Late Jomon Period (n = 5)). Cross-sectional images of the diaphysis from below the lesser trochanter to above the adductor tubercle were obtained using the method established by Imamura et al. (2019) and Imamura et al. (2021). Using Excel formulas and macros, the area of cortical bone, thickness, and degree of curvature were quantitatively analyzed. The results were compared with data on modern Japanese. The maximum thickness of cortical bone in the diaphysis and the degree of the anterior curvature were significantly greater in Late Jomon humans than in the other groups. In contrast to modern humans, the majority of Jomon femurs showed the S-shaped curvature with the medial side at the top position and the lateral side at the lower position. The present results demonstrate that Late Jomon humans had a wider range of activity than the other groups and also provide insights into diseases in the hip and knee joints of Jomon humans.

The Effect of Humanized Nursing Intervention Guided by Computed Tomography Images on Elderly Patients Undergoing Anesthesia for Femur Intertrochanteric Fractures under Intelligent Reconstruction Algorithm

This research was aimed at analyzing the effect of humanized nursing intervention combined with computed tomography (CT) imaging in the surgical anesthesia of femur intertrochanteric fractures (FIF) in the elderly. An image reconstruction algorithm was proposed based on nonlocal mean (NLM) algorithm, which was named as ONLM, and its performance was analyzed. A total of 114 elderly patients with FIF were equally and randomly divided into a humanized nursing group (57 cases) and a routine nursing group (57 cases). They were performed with CT imaging scan based on the ONLM algorithm, and the clinical indicators of the two groups of patients were recorded. The root mean square error (RMSE) and mean absolute error (MAE) of the CT images constructed using the ONLM algorithm were significantly lower than those using NLM algorithm, edge filtering algorithm, and total variation model, while the peak signal-to-noise ratio (PSNR) was the opposite (P < 0.05). The operation time, hospitalization days, intraoperative blood loss, postoperative drainage, and anesthesia preparation time of patients in the humanized nursing group were significantly lower than those in the routine nursing group. The number of patients with excellent Harris scores in the humanized nursing group was higher than that in the routine nursing group, and the number of patients with poor Harris scores was lower (P < 0.05). The language pain score, facial pain score, and visual analog simulation (VAS) scores of patients in the humanized nursing group were significantly lower than those in the routine nursing group. The numbers of postoperative hip varus and fracture nonunion cases in the humanized nursing group were significantly more than those in the routine nursing group. In short, CT images constructed by the ONLM showed higher performance than those by the traditional algorithm. In addition, CT images constructed by ONLM combined with humanized nursing intervention could more effectively improve the cooperation of patients with surgical anesthesia, reduce surgical pain and fear of patients, improve the prognosis of patients, and lower the occurrence of adverse events.

Biomechanical Stress Analysis of Platform Switch Implants of Varying Diameters on Different Densities of Bone

Purpose

The purpose of this study was to evaluate and compare the strain developed in D2 and D3 types of bones on vertical loading by platform switch implants of different diameters.

Materials and Methods

Implants of diameters 3.25 mm, 4.2 mm, and 5.0 mm and of length 11.5 mm were taken and placed each on D2 and D3 bone models. Strain gauges were attached on the buccal and the lingual sides on each of these samples, and a vertical load of 190N was placed on the samples. The strain was recorded using a data logger. The data obtained was analysed using one-way ANOVA and post hoc Tukey test.

Results

In D2 and D3 bone models, 3.25 mm significantly showed greater bone strain values. The buccal side strain was higher irrespective of the implant diameter and density of bone.

Conclusion

Within the limitations of the study, it may be concluded that the narrow diameter implant produces greater strain than 4.2 and 5.0 mm diameter implants, respectively. The buccal side consistently produced higher bone strain values.