New approaches for cement-based prophylactic augmentation of the osteoporotic proximal femur provide enhanced reinforcement as predicted by non-linear finite element simulations

In vitro mechanical analysis of X-shaped femoroplasty with polymethyl methacrylate boundary a fall on the greater trochanter. Injury 2023;54 Suppl 6:110747. [PMID: 38143120 DOI: 10.1016/j.injury.2023.04.034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

To evaluate with mechanical testing (MT) using synthetic femurs, an X-shaped femoroplasty technique with polymethyl methacrylate (PMMA), analyzing the results applied to the prophylaxis of proximal femur (PF) fractures caused by low-energy trauma. MT was performed simulating a fall on the greater trochanter, using fifteen Sawbones™ models. They were divided into three experimental groups (n = 5): control (DP) group, drilled without augmentation (DWA) group, and X-shaped augmentation (DX) group. Maximum load, stiffness, absorbed energy and displacement were analyzed primarily in all groups; and secondarily then, morphology and fracture type were verified in all groups while PMMA volume, temperature and time polymerization were analyzed only in the DX group. The MT results obtained for synthetic models respectively in the DP, DWA, and DX groups were: mean maximum load (5562.0 ± 464.8) N, (4798.0 ± 121.2) N, and (7132.0 ± 206.9) N; mean stiffness values (673 ± 64.34) N/mm, (636 ± 8.7) N/mm, and (738 ± 17.13) N/mm, and mean absorbed energy values (36,203 ± 3819) N.mm, (27,617 ± 3011) N.mm, (44,762 ± 3219) N.mm; mean displacement values (13.6 ± 1.45) N, (11.1 ± 0.5) N, and (13.2 ± 0.69) N. The mean volume, temperature reached during filling in the DX group were 9.8 mL, 42.54ºC with 1' 56" of polymerization. The fracture types were similar between the DP and DWA groups, affecting the trochanteric region, as distinctly to those in the DX group, which were restricted to the femoral neck. The values obtained in MT showed statistical significance when analyzed by one-way ANOVA (5%) for maximum load, stiffness, and absorbed energy between groups. In conclusion, X-shaped PMMA augmentation presents a protective biomechanical characteristic against PF fractures generated in synthetic models by boundary a fall on the greater trochanter.

QCT-based computational bone strength assessment updated with MRI-derived 'hidden' microporosity

Microdamage accumulated through sustained periods of cyclic loading or single overloading events contributes to bone fragility through a reduction in stiffness and strength. Monitoring microdamage in vivo remains unattainable by clinical imaging modalities. As such, there are no established computational methods for clinical fracture risk assessment that account for microdamage that exists in vivo at any specific timepoint. We propose a method that combines multiple clinical imaging modalities to identify an indicative surrogate, which we term 'hidden porosity', that incorporates pre-existing bone microdamage in vivo. To do so, we use the third metacarpal bone of the equine athlete as an exemplary model for fatigue induced microdamage, which coalesces in the subchondral bone. N = 10 metacarpals were scanned by clinical quantitative computed tomography (QCT) and magnetic resonance imaging (MRI). We used a patch-based similarity method to quantify the signal intensity of a fluid sensitive MRI sequence in bone regions where microdamage coalesces. The method generated MRI-derived pseudoCT images which were then used to determine a pre-existing damage (Dpex) variable to quantify the proposed surrogate and which we incorporate into a nonlinear constitutive model for bone tissue. The minimum, median, and maximum detected Dpex of 0.059, 0.209, and 0.353 reduced material stiffness by 5.9%, 20.9%, and 35.3% as well as yield stress by 5.9%, 20.3%, and 35.3%. Limb-specific voxel-based finite element meshes were equipped with the updated material model. Lateral and medial condyles of each metacarpal were loaded to simulate physiological joint loading during gallop. The degree of detected Dpex correlated with a relative reduction in both condylar stiffness (p = 0.001, R2 > 0.74) and strength (p < 0.001, R2 > 0.80). Our results illustrate the complementary value of looking beyond clinical CT, which neglects the inclusion of microdamage due to partial volume effects. As we use clinically available imaging techniques, our results may aid research beyond the equine model on fracture risk assessment in human diseases such as osteoarthritis, bone cancer, or osteoporosis.

[Cement augmentation and bone graft substitutes-Materials and biomechanics]

BACKGROUND

Materials with different characteristics are used for cement augmentation and as bone graft substitutes.

OBJECTIVE

Cement augmentation and bone graft substitutes are the subject of current research. The evaluation of new knowledge allows its specific application.

MATERIAL AND METHODS

Selective literature search and outline of experimental research results on cement augmentation and bone graft substitutes.

RESULTS

Augmentation and bone graft substitutes are essential components of current trauma surgical procedures. Despite intensive research all materials have specific disadvantages. Cement augmentation of implants enhances not only the anchorage but also influences the failure mode.

CONCLUSION

Cement augmentation has large potential especially in osteoporotic bone. In load-bearing regions acrylic-based cements remain the standard of choice. Ceramic cements are preferred in non-load-bearing areas. Their combination with resorbable metals offers still largely unexplored potential. Virtual biomechanics can help improve the targeted application of cement augmentation.

Finite Element Analysis of Cannulated Screws as Prophylactic Intervention of Hip Fractures

Introduction

The frequency of hip fractures, a major cause of morbidity and mortality for geriatric patients, is expected to increase exponentially in the next few decades. The aim of this study is to assess the ability of stainless-steel cannulated screws to reduce the risk of a femoral neck fracture, if placed prophylactically prior to a fall.

Materials and Methods

We created finite element models from computed tomography (CT) scan-based 3D models of a geriatric patient through 3D-image processing and model generation software. We used linear finite element simulations to analyze the effect of cannulated screws in the proximal femur in single-leg stance and lateral fall, which were processed for peak von Mises stresses and element failure.

Findings

Prophylactically placed cannulated screws significantly reduced failure in an osteoporotic proximal femur undergoing lateral fall. Three implanted screws in an inverted triangle formation decreased proximal femoral trabecular failure by 21% and cortical failure by 5%. This reduction in failure was achieved with a 55% decrease in femoral neck failure and 14% in lateral cortex failure.

Conclusion

Our results indicate that cannulated hip screws in an inverted triangle formation may strengthen an osteoporotic proximal femur in the event of a lateral fall. Mechanical testing on cadaveric or composite models is required to validate these results.

Prophylactic augmentation implants in the proximal femur for hip fracture prevention: An in silico investigation of simulated sideways fall impacts

Femoral fractures from sideways falls in the elderly are associated with significant rates of morbidity and mortality. Approaches to prevent these catastrophic injuries include pharmacological treatments, which have limited efficacy. Prophylactic femoral augmentation systems are a promising alternative that are gaining prominence by addressing the most debilitating osteoporosis-related fracture. We have developed finite element models (FEMs) of a novel experimental sideways fall simulator for cadavers. By virtue of the range of specimens and injury outcomes, these FEMs are well-suited to the evaluation of such implants. The purpose of this study was to use the FEMs to evaluate the mechanical effectiveness of three different prophylactic femoral augmentation systems. Models of the Y-Strut® (Hyprevention®, Pessac, France), Gamma Nail® (Stryker, Kalamazoo, USA), and a simple lag screw femoral fracture implant systems were placed into FEMs of five cadaveric pelvis-femur constructs embedded in a soft tissue surrogate, which were then subject to simulated sideways falls at seven impact velocities. Femur-only FEMs were also evaluated. Peak impact forces and peak acetabular forces were examined, and failure was evaluated using a strain-based criterion. We found that the femoral augmentation systems increased the peak forces prior to fracture, but were unable to prevent fracture for severe impacts. The Gamma Nail® system consistently produced the largest strength increases relative to the unaugmented femur for all five specimens in both the pendulum-drop FEMs and the femur-only simulations. In some cases, the same implant appeared to cause fractures in the acetabulum. The femur-only FEMs showed larger force increases than the pendulum-drop simulations, which suggests that the results of the femur-only simulations may not represent sideways falls as accurately as the soft tissue-embedded pendulum-drop simulations. The results from this study demonstrate the ability to simulate a high energy phenomenon and the effect of implants in an in silico environment. The results also suggest that implants could increase the force applied to the proximal femur during impact. Fracture outcomes from the tested implants can be used to inform the design of future devices, which reaffirms the value of modelling with biofidelic considerations in the implant design process. To the authors' knowledge, this is the first paper to use more complex biofidelic FEMs to assess prophylactic femoral augmentation methods.

A biomechanically-guided planning and execution paradigm for osteoporotic hip augmentation: Experimental evaluation of the biomechanics and temperature-rise

BACKGROUND

Augmentation of the proximal femur with bone cement (femoroplasty) has been identified as a potential preventive approach to reduce the risk of fracture. Femoroplasty, however, is associated with a risk of thermal damage as well as the leakage of bone cement or blockage of blood supply when large volumes of cement are introduced inside the bone.

METHODS

Six pairs of cadaveric femora were augmented using a newly proposed planning paradigm and an in-house navigation system to control the location and volume of the injected cement. To evaluate the risk of thermal damage, we recorded the peak temperature of bone at three regions of interest as well as the exposure time for temperature rise of 8 °C, 10 °C, and 12 °C in these regions. Augmentation was followed by mechanical testing to failure resembling a sideway fall on the greater trochanter.

FINDINGS

Results of the fracture tests correlated with those of simulations for the yield load (R2 = 0.77) and showed that femoroplasty can significantly improve the yield load (42%, P < 0.001) and yield energy (139%, P = 0.062) of the specimens. Meanwhile, temperature recordings of the bone surface showed that the areas close to the greater trochanter will be exposed to more critical temperature rise than the trochanteric crest and femoral neck areas.

INTERPRETATION

The new planning paradigm offers a more efficient injection strategy with injection volume of 9.1 ml on average. Meanwhile, temperature recordings of bone surfaces suggest that risk of thermal necrosis remains as a concern with femoroplasty using Polymethylmethacrylate.

Mechanical and morphological characterization of PMMA/bone composites in human femoral heads

PMMA bone cement has gained an important place in a variety of orthopaedic applications in the femur. However, appropriate data on the mechanical properties of bone-cement composites from the human femur are lacking. Therefore, the goal of this study was to determine the morphological and quasi-static compressive properties of proximal femoral bone-cement composites. Thirty trabecular bone specimens were extracted from fifteen pairs of human femoral heads using specimen-specific cutting guides to ensure an accurate alignment with the main trabecular direction (MTD). One specimen from each pair was augmented with PMMA bone cement, while the other one was left untreated. Specimens were scanned with μCT to determine morphological parameters and tested in quasi-static compression until failure. We found that the long axis of the specimens was highly aligned with the MTD (mean error < 5°). A higher compressive modulus and ultimate strength were observed for the bone-cement composite specimens (E = 5.7 ± 0.4 GPa; σ_u = 77.9 ± 5.1 MPa) compared to the bone only specimens (E = 2.9 ± 0.7 GPa; σ_u = 19.0 ± 5.8 MPa). Furthermore, the composites had a higher modulus, but lower strength than cement itself (E = 5.0 ± 0.3 GPa; σ_u = 85.9 ± 2.7 MPa) and the composite modulus was significantly correlated with the bone volume fraction (BV/TV). These results are in contrast to previous findings on human vertebral bone, where the composite was more compliant than cement and no correlation was found between BV/TV and the composite modulus. Thus, properties of bone-cement composites cannot simply be applied across different anatomical sites; the site-specific differences in bone density and trabecular alignment should be taken into account. Collectively, the present results suggest that at low BV/TV, cement dominates the composite properties, while at high BV/TV, the contribution of bone becomes apparent, revealing a positive relationship between BV/TV and the on-axis modulus.

Biomechanical in vitro examination of a standardized low-volume tubular femoroplasty

BACKGROUND

Osteoporosis is associated with the risk of fractures near the hip. Age and comorbidities increase the perioperative risk. Due to the ageing population, fracture of the proximal femur also proves to be a socio-economic problem. Preventive surgical measures have hardly been used so far.

METHODS

10 pairs of human femora from fresh cadavers were divided into control and low-volume femoroplasty groups and subjected to a Hayes fall-loading fracture test. The results of the respective localization and classification of the fracture site, the Singh index determined by computed tomography (CT) examination and the parameters in terms of fracture force, work to fracture and stiffness were evaluated statistically and with the finite element method. In addition, a finite element parametric study with different position angles and variants of the tubular geometry of the femoroplasty was performed.

FINDINGS

Compared to the control group, the work to fracture could be increased by 33.2%. The fracture force increased by 19.9%. The used technique and instrumentation proved to be standardized and reproducible with an average poly(methyl methacrylate) volume of 10.5 ml. The parametric study showed the best results for the selected angle and geometry.

INTERPRETATION

The cadaver studies demonstrated the biomechanical efficacy of the low-volume tubular femoroplasty. The numerical calculations confirmed the optimal choice of positioning as well as the inner and outer diameter of the tube in this setting. The standardized minimally invasive technique with the instruments developed for it could be used in further comparative studies to confirm the measured biomechanical results.

Finite element models for fracture prevention in patients with metastatic bone disease. A literature review

Patients with bone metastases have an increased risk to sustain a pathological fracture as lytic metastatic lesions damage and weaken the bone. In order to prevent fractures, prophylactic treatment is advised for patients with a high fracture risk. Mechanical stabilization of the femur can be provided through femoroplasty, a minimally invasive procedure where bone cement is injected into the lesion, or through internal fixation with intra- or extramedullary implants. Clinicians face the task of determining whether or not prophylactic treatment is required and which treatment would be the most optimal. Finite element (FE) models are promising tools that could support this decision process. The aim of this paper is to provide an overview of the state-of-the-art in FE modeling for the treatment decision of metastatic bone lesions in the femur. First, we will summarize the clinical and mechanical results of femoroplasty as a prophylactic treatment method. Secondly, current FE models for fracture risk assessment of metastatic femurs will be reviewed and the remaining challenges for clinical implementation will be discussed. Thirdly, we will elaborate on the simulation of femoroplasty in FE models and discuss future opportunities. Femoroplasty has already proven to effectively relieve pain and improve functionality, but there remains uncertainty whether it provides sufficient mechanical strengthening to prevent pathological fractures. FE models could help to select appropriate candidates for whom femoroplasty provides sufficient increase in strength and to further improve the mechanical benefit by optimizing the locations for cement augmentation.

Significance of preoperative planning for prophylactic augmentation of osteoporotic hip: A computational modeling study

A potential effective treatment for prevention of osteoporotic hip fractures is augmentation of the mechanical properties of the femur by injecting it with bone cement. This therapy, however, is only in research stage and can benefit substantially from computational simulations to optimize the pattern of cement injection. Some studies have considered a patient-specific planning paradigm for Osteoporotic Hip Augmentation (OHA). Despite their biomechanical advantages, customized plans require advanced surgical systems for implementation. Other studies, therefore, have suggested a more generalized injection strategy. The goal of this study is to investigate as to whether the additional computational overhead of the patient-specific planning can significantly improve the bone strength as compared to the generalized injection strategies attempted in the literature. For this purpose, numerical models were developed from high resolution CT images (n = 4). Through finite element analysis and hydrodynamic simulations, we compared the biomechanical efficiency of the customized cement-based augmentation along with three generalized injection strategies developed previously. Two series of simulations were studied, one with homogeneous and one with inhomogeneous material properties for the osteoporotic bone. The customized cement-based augmentation inhomogeneous models showed that injection of only 10 ml of bone cement can significantly increase the yield load (79.6%, P < 0.01) and yield energy (199%, P < 0.01) of an osteoporotic femur. This increase is significantly higher than those of the generalized injections proposed previously (23.8% on average). Our findings suggest that OHA can significantly benefit from a patient-specific plan that determines the pattern and volume of the injected cement.

Fracture strength of the proximal femur injected with a calcium sulfate/hydroxyapatite bone substitute

BACKGROUND

Available interventions for preventing fragility hip fractures show limited efficacy. Injection of a biomaterial as bone substitute could increase the fracture strength of the hip. This study aimed to show the feasibility of injecting a calcium sulfate/hydroxyapatite based biomaterial in the femoral neck and to calculate the consequent change in strength using the finite element method.

METHODS

Five patients were injected with 10 ml calcium sulfate/hydroxyapatite in their femoral neck. Quantitative CT scans were taken before and after injection. Five additional patients with fragility hip fractures were also scanned and the images from the non-fractured contralateral sides were used. Finite element models were created for all proximal femora with and without injection and the models were tested under stance and sideways fall loading until fracture. The change in fracture strength caused by the injection was calculated. Additionally, perturbations in volume, location, and stiffness of the injected material were created to investigate their contribution to the fracture strength increase.

FINDINGS

The 10 ml injection succeeded in all patients. Baseline simulations showed theoretical fracture strength increases of 0-9%. Volume increase, change in location and increase in stiffness of the material led to increases in fracture strength of 1-27%, -8-26% and 0-17%, respectively. Altering the location of the injection to a more lateral position and increasing the stiffness of the material led to increases in fracture strength of up to 42%.

INTERPRETATION

This study shows that an injection of calcium sulfate/hydroxyapatite is feasible and can theoretically increase the hip's fracture strength.

Biomechanical effects of osteoplasty with or without Kirschner wire augmentation on long bone diaphyses undergoing bending stress: implications for percutaneous imaging-guided consolidation in cancer patients

Background

Osteoplasty has been discouraged in long bones. However, despite a substantial lack of pre-clinical biomechanical tests, multiple clinical studies have implemented a wide range of techniques to optimise long bone osteoplasty. The aim of the present study is to evaluate the biomechanical properties of osteoplasty alone and in combination with Kirschner wires (K-wires) in a cadaveric human diaphyseal model undergoing 3-point bending stress.

Methods

Thirty unpaired human cadaveric hemi-tibia specimens were randomly assigned to receive no consolidation (group 1, n = 10), osteoplasty alone (group 2, n = 10), or K-wires augmented osteoplasty (group 3, n = 10). Specimens were tested on a dedicated servo-hydraulic machine using a 3-point bending test. Fracture load was calculated for each specimen; two-sample Wilcoxon rank-sum tests were used to assess differences between groups.

Results

Median volume of polymethyl methacrylate injected was 18 mL for group 2 (25th–50th percentile 15–21 mL) and 19 mL for group 3 (25th–50th percentile 17–21). There were no significant differences in fracture load between groups 1 and 2 (z = − 0.793; p = 0.430), between groups 1 and 3 (z = − 0.944; p = 0.347), and between groups 2 and 3 (z = − 0.454; p = 0.650). Fractures through the cement occurred in 4 of 30 cases (13.3%); there were no K-wires fractures.

Conclusions

Osteoplasty with or without K-wires augmentation does not improve the resistance of diaphyseal bone to bending stresses.

PRELIMINARY MECHANICAL TEST OF PROXIMAL FEMUR REINFORCEMENT WITH CEMENTED X-SHAPED PMMA

Objective:

To evaluate the mechanical behavior of the proximal end of the femur submitted to the X-shaped polymethylmethacrylate (PMMA) reinforcement technique.

Methods:

Fifteen synthetic femurs, with a Nacional^® density of 10 PCF, were divided into two groups: the DX group, with 5 units that were submitted to PMMA reinforcement, and the DP group, with 10 units, which were evaluated intact. The volume of PMMA required, the maximum load, and the absorbed energy to fracture were analyzed by means of a static mechanical bending test simulating a fall on the greater trochanter.

Results:

A mean of 6 ml of PMMA was used to model the X-reinforcement; it was observed that the DX group presented significantly higher maximum load (median = 1553 N, p = 0.005) and absorbed energy to fracture (median = 9.7 J; p = 0.050) than the DP group (median = 905 N and 6.6 J).

Conclusion:

X-reinforcement of the proximal end of synthetic femurs showed a statistically significant increase in the maximum load and absorbed energy to fracture in the mechanical assay when compared to the control group. Level of Evidence III, Experimental study.

Discrete particle model for cement infiltration within open-cell structures: Prevention of osteoporotic fracture

This paper proposes a discrete particle model based on the random-walk theory for simulating cement infiltration within open-cell structures to prevent osteoporotic proximal femur fractures. Model parameters consider the cement viscosity (high and low) and the desired direction of injection (vertical and diagonal). In vitro and in silico characterizations of augmented open-cell structures validated the computational model and quantified the improved mechanical properties (Young's modulus) of the augmented specimens. The cement injection pattern was successfully predicted in all the simulated cases. All the augmented specimens exhibited enhanced mechanical properties computationally and experimentally (maximum improvements of 237.95 ± 12.91% and 246.85 ± 35.57%, respectively). The open-cell structures with high porosity fraction showed a considerable increase in mechanical properties. Cement augmentation in low porosity fraction specimens resulted in a lesser increase in mechanical properties. The results suggest that the proposed discrete particle model is adequate for use as a femoroplasty planning framework.

Numerical investigation of the effect of bone cement porosity on osteoporotic femoral augmentation

Femoroplasty is the injection of bone cement into the proximal femur, enhances the bone load capacity, and is typically applied to osteoporotic femora. To minimize the required injected volume of bone cement and maximize the load capacity enhancement, an optimization problem must be solved, where the modulus of elasticity of the augmented bone is a key element. This paper, through the numerical investigation of a fall on the greater trochanter of an osteoporotic femur, compares different ways to calculate this modulus and introduces an approach, based on the concept of bone cement porosity, which provides results statistically similar to those obtained with other considerations. Based on this approach, the present paper quantifies the correlation between degree of osteoporosis and optimum volume of bone cement. It concludes with an exhaustive search that reveals the effect of the bone cement porosity on the optimum volume of PMMA, for various combinations of the frontal and transverse angles of the fall on the greater trochanter.