A three-dimensional finite element model for biomechanical analysis of the hip

The Role of Contrast-enhanced Ultrasound in the Femoral Head Perfusion Evaluation: A Pilot Study

OBJECTIVES

We explored the value of contrast-enhanced ultrasound (CEUS) in evaluating femoral head (FH) perfusion, guiding interventions and follow-up for infants with developmental dysplasia of the hip (DDH) and septic arthritis of the hip (SAH). The aim was to provide robust evidence for clinical assessment.

METHODS

Ten infants, including 7 with DDH and 3 with SAH, were prospectively enrolled, with their bilateral hips alternately scanned during the CEUS exams. Twenty hips were classified into the case group (n = 11) and the control group (n = 9). Pre- and post-interventional studies were performed in DDH infants requiring interventions. FH perfusion was assessed by the perfusion area ratio (PAR) and quadrant location of microbubble-defect regions.

RESULTS

In the case group, 25 CEUS studies were conducted, including 11 baseline, 7 follow-up and 7 post-intervention studies. The PAR significantly decreased in the case group (49.79% vs. 100.00%, p < 0.05). The microbubble-defect regions averagely affected 2 quadrants, primarily quadrat No. 3 (30%) and No. 4 (32%). Seven hip abduction angle adjustments were made based on pre-interventional studies, resulting in a significant increase in PAR in post-interventional studies (37.63% vs. 60.24%, p < 0.05). PAR increased in follow-up studies compared to baseline values (45.61% vs. 76.07%, p < 0.05). The inter- and intra-observer reproducibility of PAR measurements were excellent (intraclass correlation coefficient, both 0.97).

CONCLUSION

CEUS proves to be a promising technique for quantitatively detecting FH perfusion in DDH and SAH infants with high reproducibility. It is valuable for baseline, intra-intervention and follow-up studies, aiming in clinical conditions and therapeutic effect evaluation.

Design optimization procedure for an orthopedic insole having a continuously variable stiffness/shape to reduce the plantar pressure in the foot of a diabetic patient

Foot ulcers and lower-limb amputations are among the major problems in diabetic patients. Orthopedic insoles can reduce the risk of diabetic foot ulcers in patients through pressure redistribution on the bottom of the foot. The purpose of this study was to propose an optimization method to design the dedicated insoles for diabetic patients in order to decrease the maximum plantar pressure. At first, a three-dimensional finite element model of bones, ligaments and soft tissue of a diabetic patient's foot was created using CT scan images. Then, the foot plantar pressure was calculated by means of a finite element software. Next, the stiffness and shape of a simple flat insole were separately modified to reduce the maximum foot plantar pressure. The optimization method resulted in a dedicated insole design with a continuously variable stiffness/shape within its area that creates a smooth pressure distribution for the patient comfort. The results showed a 40% reduction in the maximum foot pressure, which we attribute to the modification of insole stiffness. In addition, the optimal shape of the proposed insole decreased the maximum plantar pressure by 25% compared to the flat insole.

Superimposition of maximal stress and necrosis areas at the top of the femoral head in hip aseptic osteonecrosis

INTRODUCTION

Recent reports described possible mechanical factors in the development and aggravation of osteonecrosis of the femoral head (OFH), but these have yet to be confirmed on dedicated mechanical study. We therefore developed a 3D finite element model based on in-vivo data from patients with incipient OFH, with a view to determining whether the necrosis area was superimposed on the maximal stress area on the femoral head.

HYPOTHESIS

The location of the necrosis area is determined by stress on the femoral head.

MATERIAL AND METHOD

All patients from the rheumatology department with early stage OFH in our center were investigated. Analysis of CT scans showed stress distribution on the head by 3D finite elements models, enabling determination of necrosis volume within the maximal stress area and of the percentage intersection of necrosis within the stress area (%I n/s: necrosis volume in stress area divided by total stress area volume and multiplied by 100) and of stress within the necrosis area (%I s/n: stress volume in necrosis area divided by total necrosis area volume and multiplied by 100).

RESULTS

Nineteen of the 161 patients assessed retrospectively for the period between 2006 and 2015 had incipient unilateral OFH, 10 of whom (4 right, 6 left) had CT scans of sufficient quality for inclusion. Mean age was 52 years (range, 37-81 years). Mean maximal stress was 1.63MPa, mean maximal exported stress volume was 2,236.9 mm³ and mean necrosis volume 6,291.1 mm³. Mean %I n/s was 83% and mean %I s/n 35%, with no significant differences according to gender, age, side or stress volume. There was a strong inverse correlation between necrosis volume and %I s/n (R²=-0.92) and a strong direct correlation between exported stress volume and %I s/n (R²=0.55). %I s/n was greater in small necrosis (<7,000mm³).

CONCLUSION

OFH seems to develop within the maximal stress area on the femoral head. The present results need confirmation by larger-scale studies. We consider it essential to take account of these mechanical parameters to reduce failure rates in conservative treatment of OFH.

LEVEL OF EVIDENCE

IV.

FEBio: History and Advances

The principal goal of the FEBio project is to provide an advanced finite element tool for the biomechanics and biophysics communities that allows researchers to model mechanics, transport, and electrokinetic phenomena for biological systems accurately and efficiently. In addition, because FEBio is geared toward the research community, the code is designed such that new features can be added easily, thus making it an ideal tool for testing novel computational methods. Finally, because the success of a code is determined by its user base, integral goals of the FEBio project have been to offer support and outreach to our community; to provide mechanisms for dissemination of results, models, and data; and to encourage interaction between users. This review presents the history of the FEBio project, from its initial developments through its current funding period. We also present a glimpse into the future of FEBio.

The Applications of Finite Element Analysis in Proximal Humeral Fractures

Proximal humeral fractures are common and most challenging, due to the complexity of the glenohumeral joint, especially in the geriatric population with impacted fractures, that the development of implants continues because currently the problems with their fixation are not solved. Pre-, intra-, and postoperative assessments are crucial in management of those patients. Finite element analysis, as one of the valuable tools, has been implemented as an effective and noninvasive method to analyze proximal humeral fractures, providing solid evidence for management of troublesome patients. However, no review article about the applications and effects of finite element analysis in assessing proximal humeral fractures has been reported yet. This review article summarized the applications, contribution, and clinical significance of finite element analysis in assessing proximal humeral fractures. Furthermore, the limitations of finite element analysis, the difficulties of more realistic simulation, and the validation and also the creation of validated FE models were discussed. We concluded that although some advancements in proximal humeral fractures researches have been made by using finite element analysis, utility of this powerful tool for routine clinical management and adequate simulation requires more state-of-the-art studies to provide evidence and bases.

Quantitative study of osteoporosis model based on synchrotron radiation

To investigate the changes of different periods of primary osteoporosis, we made quantitative analysis of osteoporosis using synchrotron radiation computed tomography (SRCT), together with histomorphometry analysis and finite element analysis (FEA). Tibias, femurs and lumbar vertebras were dissected from sham-ovariectomy rats and ovariectomized rats suffering from osteoporosis at certain time points. The samples were scanned by SRCT and then FEA was applied based on reconstructed slices. Histomorphometry analysis showed that the structure of some trabecular in osteoporosis degraded as the bone volume decreased, for femurs, the bone volume fraction (BV/TV) decreased from 69% to 43%. That led to the increase of the thickness of trabecular separation (from 45.05μm to 97.09μm) and the reduction of the number of trabecular (from 7.99 mm(-1) to 5.97mm(-1)). Simulation of various mechanical tests indicated that, with the exacerbation of osteoporosis, the bones' ability of resistance to compression, bending and torsion gradually became weaker. The compression stiffness decreased from 1770.96 Fμm(-1) to 697.41 Fμm(-1), and it matched the histomorphometry analysis. This study suggested that the combination of both analysis could quantitatively analyze the bone strength in good accuracy.

3D patient-specific model of the tibia from CT for orthopedic use

OBJECTIVES

3D patient-specific model of the tibia is used to determine the torque needed to initialize the tibial torsion correction.

METHODS

The finite elements method is used in the biomechanical modeling of tibia. The geometric model of the tibia is obtained from CT images. The tibia is modeled as an anisotropic material with non-homogeneous mechanical properties.

CONCLUSIONS

The maximum stress is located in the shaft of tibia diaphysis. With both meshes are obtained similar results of stresses and displacements. For this patient-specific model, the torque must be greater than 30 Nm to initialize the correction of tibial torsion deformity.