A biomechanical evaluation of femoroplasty under simulated fall conditions

How accurately do finite element models predict the fall impact response of ex vivo specimens augmented by prophylactic intramedullary nailing?

Hip fracture prevention approaches like prophylactic augmentation devices have been proposed to strengthen the femur and prevent hip fracture in a fall scenario. The aim of this study was to validate the finite element model (FEM) of specimens augmented by prophylactic intramedullary nailing in a simulated sideways fall impact against ex vivo experimental data. A dynamic inertia-driven sideways fall simulator was used to test six cadaveric specimens (3 females, 3 males, age 63-83 years) prophylactically implanted with an intramedullary nailing system used to augment the femur. Impact force measurements, pelvic deformation, effective pelvic stiffness, and fracture outcomes were compared between the ex vivo experiments and the FEMs. The FEMs over-predicted the effective pelvic stiffness for most specimens and showed variability in terms of under- and over-predicting peak impact force and pelvis compression depending on the specimen. A significant correlation was found for time to peak impact force when comparing ex vivo and FEM data. No femoral fractures were found in the ex vivo experiments, but two specimens sustained pelvic fractures. These two pelvis fractures were correctly identified by the FEMs, but the FEMs made three additional false-positive fracture identifications. These validation results highlight current limitations of these sideways fall impact models specific to the inclusion of an orthopaedic implant. These FEMs present a conservative strategy for fracture prediction in future applications. Further evaluation of the modelling approaches used for the bone-implant interface is recommended for modelling augmented specimens, alongside the importance of maintaining well-controlled experimental conditions.

Different polymethylmethacrylate (PMMA) reinforcement strategies for long bone osteoplasty procedures: a controlled laboratory comparison using the 4-point bending test

BACKGROUND

Cementoplasty has been successfully used for treating fractures in various parts of the human body, although the use in weight-bearing long bones is a subject of controversial debate. Strategies to improve the mechanical properties of polymethylmethacrylate-based bone cement (BC) comprise changing the chemical composition or the application of metal reinforcement strategies. In clinical practice reinforced bone cement is used despite biomechanical basic research regarding this topic being scare.

OBJECTIVE

The aim of the present study was to evaluate the biomechanical properties of two different reinforcement strategies against non-reinforced polymethylmethacrylate-based BC subjected to bending stress.

METHODS

In this controlled comparative laboratory analysis, we evaluated two types of reinforcement strategies in comparison to a control group (C). BC was reinforced with a Kirschner wire (group CW) or with a prestressed twinned steel cable (group CC); control group C was native polymethylmethacrylate-based BC. All the samples were prepared using a custom-made mould and underwent 4-point bending stress until fracture using a testing machine. Flexural strength, maximum strain, and Young's modulus were assessed for the three groups and compared using the Kruskal‒Wallis test.

RESULTS

The mean flexural strength in MPa was 48 ± 12 in C, 64 ± 6 in CW, and 63 ± 14 in CC. A significantly greater flexural strength of + 33% was found in both reinforced groups than in the C group (C vs. CW p = 0.011, C vs. CC p = 0.023). Regarding the flexural strength, no statistically significant difference could be found between the two reinforcement strategies CW and CC (p = 0.957). The maximum strain was 3.0% in C and CW and 3.8% in CC and no difference between the three groups was observed (p = 0.087). The Young's modulus in GPa was 2.7 for C, 2.8 for CW, and 2.4 for CC. The comparison of Young's module using the Kruskal-Wallis test showed no statistically significant difference between CC, CW and C (p = 0.051).

CONCLUSIONS

We detected an improvement in flexural strength in the reinforced groups. Both reinforcement through K-wire and prestressed cables promoted increased flexural strength. Furthermore, less material failure was observed with possible realignment and subsequent residual stability despite bone cement fracture. From a biomechanical view, the concept of macro metal reinforcement of osteoplasty is viable.

Minimally invasive interventional guided imaging therapies of musculoskeletal tumors

Historically, musculoskeletal (MSK) tumors, which include both bone and soft tissue tumors, have been managed as distinct entities. The incidence of metastases, particularly bone metastasis, in patients with MSK tumors can result in the emergence of significant complications such as pain, impairment of vital anatomical structures, or pathological fractures. Given these issues, a diverse team of experts is typically engaged in intricate treatment decision-making concerning the necessity of surgery, radiation, chemotherapy, or a mix of these methodologies. Nevertheless, percutaneous image-guided minimally invasive interventional therapy for MSK tumors represent a promising approach for treating such tumors. Over the past decade, significant progress has been made in this technique, leading to its growing acceptance in ordinary clinical practice. MSK tumors can be effectively treated by the use of ablation techniques, either as standalone procedures or in conjunction with other percutaneous treatments. Various image-guided techniques have been employed to observe the ablation zone and nearby structures, such as fluoroscopy, ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI). However, CT is the favored method due to its widespread availability and ability to visualize the tumor and its environs. The procedures employed include ethanol injection, radiofrequency ablation, microwave ablation, cryoablation, and magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU). The technique can be performed in combination with cementation, with or without additional metallic stabilizing devices, depending on the location of the lesion. Improved local tumor control can be attained by combining ablation with bland embolization or transarterial chemoembolization. This article provides an overview of the fundamental elements of minimally invasive interventional guided imaging therapy for MSK malignancies.

Periprosthetic fracture following arthroplasty for femoral neck fracture: is a cemented stem protective?

BACKGROUND

Periprosthetic femoral fractures (PFF) carry significant morbidity following arthroplasty for femoral neck fracture (FNF). This study assessed fracture complications following arthroplasty for FNF and the effect of cement fixation of the femoral component on intraoperative and post-operative PFF.

METHODS

Between February 2014 and September 2021, 740 patients with a FNF who underwent arthroplasty were analyzed for demographics, surgical management, use of cement for fixation of the femoral component, and subsequent PFF. Variables were compared with Mann-Whitney or Chi-square as appropriate. Multivariate logistic regression was used to assess independent risk factors associated with intraoperative or post-operative PFF.

RESULTS

There were 163 THAs (41% cemented) and 577 HAs (95% cemented). There were 28 PFFs (3.8%): 18 post-operative and 10 intraoperative. Fewer post-operative PFFs occurred with cemented stems (1.63% vs. 6.30%, p = 0.002). Mean time from surgery to presentation with post-operative PFF was 14 months (0-45 months). Mean follow-up time was 10.3 months (range: 0-75.7 months). In multivariate regression, use of cement and THA was independently associated with decreased post-operative PFF (cement: OR 0.112, 95% CI 0.036-0.352, p < 0.001 and THA: OR 0.249, 95% CI 0.064-0.961, p = 0.044). More intraoperative fractures occurred during THA (3.68% vs. 0.69%, p = 0.004) and non-cemented procedures (5.51% vs. 0.49%, p < 0.001). In multivariate regression, use of cement was protective against intraoperative fracture (OR 0.100, CI 0.017-0.571, p = 0.010).

CONCLUSIONS

In patients with a FNF treated with arthroplasty, cementing the femoral component is associated with a lower risk of intraoperative and post-operative PFF. Choice of procedure may be based on patient factors and surgeon preference.

Is Regional Bone Mineral Density the Differentiating Factor Between Femoral Neck and Femoral Trochanteric Fractures?

Background Osteoporosis is globally recognized as a prevalent bone disease, and proximal femoral fractures constitute a serious complication associated with it. In recent years, the frequency of hip fractures has increased rapidly, with ramifications that extend into the social and economic aspects of both patients' lives and healthcare systems. The primary goal of this study is to discover whether bone mineral density (BMD) in specific regions of the hip could be related to femoral neck or trochanteric fractures. Methodology This prospective cohort study employed dual-energy X-ray absorptiometry (DEXA) measurements on 70 individuals with proximal femoral fractures. The participants sought treatment at the emergency department of our unit for hip fractures and adhered to our predefined eligibility criteria. These criteria primarily included (i) age exceeding 60 years and (ii) a diagnosis of either femoral neck or trochanteric fracture attributed to (iii) a low-energy lateral fall and (iv) a previously established state of complete ambulation before the occurrence of the fracture. In this context, we recorded the BMD of the hip, as well as the BMD values of the upper and lower halves of the neck, trochanteric region, and diaphysis. For the comparison of the categorical variables, Pearson's χ2 criterion was used, whereas Student's t-test was applied for the comparison of means of quantitative variables across fracture types. Results No statistical differences were identified when comparing regional BMDs and T-scores with the fracture type. This conclusion was also reconfirmed concerning age, gender, and Tonnis classification. Only a moderate correlation was observed, demonstrating lower values of regional BMDs in women compared to men. Conclusions The inability of our study to establish a direct correlation between BMD measurements across diverse areas of the proximal femur underlines the imperative need for subsequent investigations. These studies should not only integrate more precise techniques for measuring and mapping the BMD of different hip regions but should also encompass a comprehensive examination that would consider both intrinsic and extrinsic characteristics of the proximal femur.

Evaluating femoral augmentation to prevent geriatric hip fracture: A scoping review of experimental methods

Various femoral augmentation designs have been investigated over the past decade for the prevention of geriatric hip fracture. The experimental methods used to evaluate the efficacy of these augmentations have not been critically evaluated or compared in terms of biofidelity, robustness, or ease of application. Such parameters have significant relevance in characterizing future clinical success. In this study we aimed to use a scoping review to summarize the experimental studies that evaluate femoral augmentation approaches, and critically evaluate commonly applied protocols and identify areas for concordance with the clinical situation. We conducted a literature search targeting studies that used experimental test methods to evaluate femoral augmentation to prevent geriatric fragility fracture. A total of 25 studies met the eligibility criteria. The most commonly investigated augmentation to date is the injection of bone cement or another material that cured in situ, and a popular subsequent method for biomechanical evaluation was to load the augmented proximal femur until fracture in a sideways fall configuration. We noted limitations in the clinical relevance of sideways fall scenarios being modeled and large variance in the concordance of many of the studies identified. Our review brings about recommendations for enhancing the fidelity of experimental methods modeling clinical sideways falls, which include an improved representation of soft tissue effects, using outcome metrics beyond load-to-failure, and applying loads inertially. Effective augmentations are encouraging for their potential to reduce the burden of hip fracture; however, the likelihood of this success is only as strong as the methods used in their evaluation.

A Surgical Robotic System for Osteoporotic Hip Augmentation: System Development and Experimental Evaluation

Minimally-invasive Osteoporotic Hip Augmentation (OHA) by injecting bone cement is a potential treatment option to reduce the risk of hip fracture. This treatment can significantly benefit from computer-assisted planning and execution system to optimize the pattern of cement injection. We present a novel robotic system for the execution of OHA that consists of a 6-DOF robotic arm and integrated drilling and injection component. The minimally-invasive procedure is performed by registering the robot and preoperative images to the surgical scene using multiview image-based 2D/3D registration with no external fiducial attached to the body. The performance of the system is evaluated through experimental sawbone studies as well as cadaveric experiments with intact soft tissues. In the cadaver experiments, distance errors of 3.28mm and 2.64mm for entry and target points and orientation error of 2.30° are calculated. Moreover, the mean surface distance error of 2.13mm with translational error of 4.47mm is reported between injected and planned cement profiles. The experimental results demonstrate the first application of the proposed Robot-Assisted combined Drilling and Injection System (RADIS), incorporating biomechanical planning and intraoperative fiducial-less 2D/3D registration on human cadavers with intact soft tissues.

The efficacy of femoral augmentation for hip fracture prevention using ceramic-based cements: A preliminary experimentally-driven finite element investigation

Femoral fractures due to sideways falls continue to be a major cause of concern for the elderly. Existing approaches for the prevention of these injuries have limited efficacy. Prophylactic femoral augmentation systems, particularly those involving the injection of ceramic-based bone cements, are gaining more attention as a potential alternative preventative approach. We evaluated the mechanical effectiveness of three variations of a bone cement injection pattern (basic ellipsoid, hollow ellipsoid, small ellipsoid) utilizing finite element simulations of sideways fall impacts. The basic augmentation pattern was tested with both high- and low-strength ceramic-based cements. The cement patterns were added to the finite element models (FEMs) of five cadaveric femurs, which were then subject to simulated sideways falls at seven impact velocities ranging from 1.0 m/s to 4.0 m/s. Peak impact forces and peak acetabular forces were examined, and failure was evaluated using a strain-based criterion. We found that the basic HA ellipsoid provided the highest increases in both the force at the acetabulum of the impacted femur ("acetabular force", 55.0% ± 22.0%) and at the force plate ("impact force", 37.4% ± 15.8%). Changing the cement to a weaker material, brushite, resulted in reduced strengthening of the femur (45.2% ± 19.4% acetabular and 30.4% ± 13.0% impact). Using a hollow version of the ellipsoid appeared to have no effect on the fracture outcome and only a minor effect on the other metrics (54.1% ± 22.3% acetabular force increase and 35.3% ± 16.0% impact force increase). However, when the outer two layers of the ellipsoid were removed (small ellipsoid), the force increases that were achieved were only 9.8% ± 5.5% acetabular force and 8.2% ± 4.1% impact force. These results demonstrate the importance of supporting the femoral neck cortex to prevent femoral fractures in a sideways fall, and provide plausible options for prophylactic femoral augmentation. As this is a preliminary study, the surgical technique, the possible effects of trabecular bone damage during the augmentation process, and the effect on the blood supply to the femoral head must be assessed further.

Finite Element Evaluation of the Femoral Neck System as Prophylactic Fixation to Prevent Contralateral Hip Fractures

Introduction

Hip fractures cause significant morbidity and mortality for geriatric patients, and incidence is increasing as the population ages. Following a primary hip fracture, up to 20% may suffer a contralateral hip fracture within 5 years despite fracture risk reduction measures, including fall prevention and osteoporosis pharmacologic treatment. The aim of this study is to assess whether insertion of the Femoral Neck System (Depuy Synthes, West Chester, PA) into the contralateral proximal femur may strengthen the bone and decrease the incidence of contralateral hip fractures.

Materials and Methods

ScanIP, an image processing software was used to produce 3-dimensional models of a cadaver femur with the implanted device. Models were meshed and exported to Abaqus for finite element analysis to evaluate the device’s ability to reduce stress in the proximal femur. Results were analyzed for element-wise volume and von-Mises stresses.

Results

The implant reduced peak stress and bone failure at all levels of bone quality. Specifically in osteoporotic bone, the implant decreased peak stress by 27%, proximal femur trabecular bone failure by 5% and cortical bone failure by 100% in the femoral neck.

Conclusions

Our results from computer generated finite element analyses indicate that the Femoral Neck System may strengthen an osteoporotic proximal femur in the event of a lateral fall. Further investigation with expanded finite element analysis and cadaveric biomechanical studies are needed 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.

Augmentation of core decompression with synthetic bone graft does not improve mechanical properties of the proximal femur

Core decompression is a minimally invasive surgical technique used to treat patients with avascular necrosis of the femoral head. The procedure requires an entry hole in the lateral cortex of the femur which potentially leaves patients susceptible to subtrochanteric fractures. The purpose of this study was to determine if filling the core decompression tract with synthetic bone-graft mechanically strengthens the proximal femur. Twenty composite synthetic femurs underwent a core decompression procedure; ten were augmented with synthetic bone-graft (PRO-DENSE™, Wright Medical) and ten femurs were left unfilled as a control group. Compressive testing to failure was performed using a mechanical testing machine. Stiffness, fracture load, and toughness did not significantly differ between groups. More subtrochanteric fractures were seen in the control group (6 of 10 specimens) compared to the bone-graft augmented group (2 of 10 specimens). In conclusion, augmentation of a core decompression tract does not improve mechanical properties in a synthetic bone model but may be protective of subtrochanteric fracture.

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.

Periprosthetic femoral fractures in sideways fall configuration: comparative numerical analysis of the influence of femoral stem design

INTRODUCTION

The aim of this study was to investigate the mechanisms of periprosthetic fractures occurring as a result of a sideways fall in total hip arthroplasty patients, and to compare the predictions of numerical models in terms of load distribution on the implanted femur with clinical data.

MATERIALS AND METHODS

3 numerical models were built: 1 for intact femur and 2 for implanted femur with a straight stem (resembling PBF, Permedica) and with an anatomical stem (resembling ABG II, Stryker). 4 loading configurations were simulated; 1 simulates a vertical load, and 3 simulate a fall with impact on the greater trochanter in different directions. Stress state calculated in the implanted femur was compared for the 2 models with reference to the intact case. These were compared with clinical data collected at a single centre (Istituto Ortopedico Gaetano Pini, Milan, Italy) where 41 patients were investigated after periprosthetic fracture: 26 patients had a straight uncemented stem and 15 an anatomical uncemented stem.

RESULTS

The maximum calculated strain in compression in the case of ABG II implanted femur was 2 times higher than in the presence of PBF stem in the vertical loading configuration. For configurations of sideways fall, in both models, there was a progressive increase of stress state in the bone with increasing angle. Simulations of sideways fall elicited results in accordance with clinical observations: due to the peculiar stem design and consequent state of stress in the bone, anatomical stems seem to induce trochanteric fractures more frequently, while for straight stems type B fractures are more likely to occur.

CONCLUSIONS

Clinical findings confirmed numerical model predictions: stem design seems to highly influence distribution of stress in the bone and consequent localisation of the fracture site.

Augmented versus non-augmented percutaneous cementoplasty for the treatment of metastatic impending fractures of proximal femur: A systematic review

INTRODUCTION

Percutaneous cementoplasty (PC) has been widely used for the stabilization of impending fractures of the proximal femur due to metastatic lesions. Augmented percataneous cementoplasty (APC) with fixation devices aims to improve mechanical consolidation and stability of the construct. However, the clinical benefit of the combined technique has not been clearly established. The purpose of the current review was to compare the efficacy between APC and PC for impending pathologic proximal femoral fractures from metastatic malignancy, in terms of pain relief, operative time and fracture related complication rates.

MATERIAL AND METHODS

Medline, Scopus, and the Cochrane central register of controlled trials were searched for clinical studies up to July 2019. Studies relevant to cementoplasty of the proximal femur were included. The primary outcome of the study was pain relief as assessed using the Visual Analogue Scale (VAS) change. Secondary outcomes included incidence of post-intervention fracture, operative time and complication rate.

RESULTS

Twelve studies with a total of 343 patients were included. No difference was found for all outcomes. For pain relief, pooled results showed a mean difference in VAS score -4.6 ± 1.7 for PC, and -4.3 ± 2.5 for APC (p = 0.41). Post-intervention fractures of the proximal femur occurred in 7% of patients with PC and in 5% of patients with APC (p = 0.4), and the mean duration of interventions was 57.9 ± 8.4 and 56.5 ± 27.5 min, respectively (p = 0.58). Cement leakage into the hip joint or the soft tissues occurred in 5% of cases in PC group and in 8% of cases in APC group (p = 0.16). Six patients in the APC group (4%) experienced major systemic complications, which were treated successfully.

CONCLUSIONS

APC does not seem to improve pain relief, fracture incidence, and operative time when compared with PC. Both techniques appeared effective in terms of resolution of symptoms, prevention of pathologic fractures, and early facilitation of weight-bearing. PC showed more clinical safety, as no major systemic complications occurred. However, due to the relative paucity of large clinical trials, the decision of augmentation of cementoplasty should be individualized according to the size and location of metastatic lesions and the overall medical condition of patients.

Treatment of bone loss in proximal femurs of postmenopausal osteoporotic women with AGN1 local osteo-enhancement procedure (LOEP) increases hip bone mineral density and hip strength: a long-term prospective cohort study

This first-in-human study of AGN1 LOEP demonstrated that this minimally-invasive treatment durably increased aBMD in femurs of osteoporotic postmenopausal women. AGN1 resorption was coupled with new bone formation by 12 weeks and that new bone was maintained for at least 5-7 years resulting in substantially increased FEA-estimated femoral strength.

INTRODUCTION

This first-in-human study evaluated feasibility, safety, and in vivo response to treating proximal femurs of postmenopausal osteoporotic women with a minimally-invasive local osteo-enhancement procedure (LOEP) to inject a resorbable triphasic osteoconductive implant material (AGN1).

METHODS

This prospective cohort study enrolled 12 postmenopausal osteoporotic (femoral neck T-score ≤ - 2.5) women aged 56 to 89 years. AGN1 LOEP was performed on left femurs; right femurs were untreated controls. Subjects were followed-up for 5-7 years. Outcomes included adverse events, proximal femur areal bone mineral density (aBMD), AGN1 resorption, and replacement with bone by X-ray and CT, and finite element analysis (FEA) estimated hip strength.

RESULTS

Baseline treated and control femoral neck aBMD was equivalent. Treated femoral neck aBMD increased by 68 ± 22%, 59 ± 24%, and 58 ± 27% over control at 12 and 24 weeks and 5-7 years, respectively (p < 0.001, all time points). Using conservative assumptions, FEA-estimated femoral strength increased by 41%, 37%, and 22% at 12 and 24 weeks and 5-7 years, respectively (p < 0.01, all time points). Qualitative analysis of X-ray and CT scans demonstrated that AGN1 resorption and replacement with bone was nearly complete by 24 weeks. By 5-7 years, AGN1 appeared to be fully resorbed and replaced with bone integrated with surrounding trabecular and cortical bone. No procedure- or device-related serious adverse events (SAEs) occurred.

CONCLUSIONS

Treating femurs of postmenopausal osteoporotic women with AGN1 LOEP results in a rapid, durable increase in aBMD and femoral strength. These results support the use and further clinical study of this approach in osteoporotic patients at high risk of hip fracture.

Local implantation of autologous adipose-derived stem cells increases femoral strength and bone density in osteoporotic rats: A randomized controlled animal study

BACKGROUND

Deficient osteogenic capacity of bone marrow stem cells plays a critical role in the pathophysiology of osteoporosis. Adipose-derived stem cells (ADSCs) have emerged as a promising source of skeletal progenitor cells. The capacity of ADSCs to undergo osteogenic differentiation and induce mineralized tissue formation may be beneficial in the treatment of osteoporosis. We question whether administration of autologous ADSCs into the proximal femur of osteoporotic rats will induce osteogenesis and enhance bone quality and strength.

MATERIALS AND METHODS

Thirty ovariectomized female rats were randomly assigned to one of the two treatment groups: (1) percutanous implantation of autogenous ADSCs-seeded scaffold into the proximal femur and (2) percutanous implantation of non-seeded scaffold. The contralateral untreated femur served as control. The effect of treatment on bone characteristics was assessed at 12-week follow-up by micro-computed tomography analysis, mechanical testing, and histological analysis.

RESULTS

The mean cortical thickness, total bone volume density, and bone load to failure in femora injected with autologous ADSCs-seeded scaffold was significantly higher compared to femora injected with non-seeded scaffold and compared to the untreated control femora ( p < 0.01). Histological examination of the injected specimens revealed complete osseo-integration of the scaffolds with direct conversion of the ADSCs into osteoblasts and no inflammatory response.

CONCLUSIONS

Autogenous ADSCs implantation into the proximal femur of rats with ovariectomy-related osteoporosis promoted bone regeneration and increased bone strength at short-term follow-up. These findings highlight the potential benefit of autogenous ADSCs in the treatment of osteoporosis.

LEVEL OF EVIDENCE

Level I, randomized controlled trial, animal study.

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.

Percutaneous extra-spinal cementoplasty in patients with cancer: A systematic review of procedural details and clinical outcomes

PURPOSE

To perform a systematic review of technical details and clinical outcomes of percutaneous extra-spinal cementoplasty in patients with malignant lesions.

MATERIALS AND METHODS

PUBMED, MEDLINE, MEDLINE in-process, EMBASE and the Cochrane databases were searched between January 1990 and February 2019 using the keywords «percutaneous cementoplasty», «percutaneous osteoplasty» and «extra-spinal cementoplasty». Inclusion criteria were: retrospective/prospective cohort with more than 4 patients, published in English language, reporting the use of percutaneous injection of cement inside an extra-spinal bone malignant tumour using a dedicated bone trocar, as a stand-alone procedure or in combination with another percutaneous intervention, in order to provide pain palliation and/or bone consolidation.

RESULTS

Thirty articles involving 652 patients with a total of 761 lesions were reviewed. Mean size of lesion was 45mm (range of mean size among publications: 29-73mm); 489 lesions were located in the pelvis, 262 in the long bones of the limbs and 10 in other locations. Cementoplasty was reported as a stand-alone procedure for 60.1% of lesions, and combined with thermal ablation for 26.2% of lesions, implant devices for 12.3% of lesions, and balloon kyphoplasty for 1.4% of lesions. The mean volume of injected cement was 8.8mL (range of mean volume among publications: 2.7-32.2mL). The preoperative visual analogic scores ranged between 3.2 and 9.5. Postoperative scores at last available follow-up ranged from 0.4 to 5.6. Thirteen papers reported a reduction of the visual analogic scores of 5 points or more. Nerve injury was the most frequent symptomatic leakage (0.6%).

CONCLUSION

Percutaneous extra-spinal cementopasty is predominantly performed as a stand-alone procedure and for lesions in the bony pelvis. It appears to be an effective tool to manage pain associated with malignant bone tumours. There is however a lack of standardization of the technique among the different publications.

In vitro injection of osteoporotic cadaveric femurs with a triphasic calcium-based implant confers immediate biomechanical integrity

Current pharmaceutical therapies can reduce hip fractures by up to 50%, but compliance to treatment is low and therapies take up to 18 months to reduce risk. Thus, alternative or complementary approaches to reduce the risk of hip fracture are needed. The AGN1 local osteo-enhancement procedure (LOEP) is one such alternative approach, as it is designed to locally replace bone lost due to osteoporosis and provide immediate biomechanical benefit. This in vitro study evaluated the initial biomechanical impact of this treatment on human cadaveric femurs. We obtained 45 pairs of cadaveric femurs from women aged 77.8 ± 8.8 years. One femur of each pair was treated, while the contralateral femur served as an untreated control. Treatment included debridement, irrigation/suction, and injection of a triphasic calcium-based implant (AGN1). Mechanical testing of the femora was performed in a sideways fall configuration 24 h after treatment. Of the 45 pairs, 4 had normal, 16 osteopenic, and 25 osteoporotic BMD T-scores. Altogether, treatment increased failure load on average by 20.5% (p < 0.0001). In the subset of osteoporotic femurs, treatment increased failure load by 26% and work to failure by 45% (p < 0.01 for both). Treatment did not significantly affect stiffness in any group. These findings provide evidence that local delivery of the triphasic calcium-based implant in the proximal femur is technically feasible and provides immediate biomechanical benefit. Our results provide strong rationale for additional studies investigating the utility of this approach for reducing the risk of hip fracture. © 2019 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society.

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.

Surgical prevention of femoral neck fractures in elderly osteoporotic patients: a randomised controlled study on the prevention nail system device

INTRODUCTION:

Hip fractures represent an enormous challenge for our health care system. The aim of this randomised controlled trial was to assess both efficacy and safety of a novel device called Prevention Nail System (PNS) and developed for the surgical prevention of a contralateral femoral neck fracture (FNF) in elderly osteoporotic patients.

METHODS:

Primary outcome was to evaluate, in patients suffering from osteoporotic FNF, the effectiveness of PNS in reducing the incidence of a contralateral hip fracture. Secondary outcome was to evaluate the safety of this device therefore intra- and postoperative complications were recorded.

RESULTS:

72 patients, with an age ⩾65 years old, were enrolled (38 study group (group A) and 34 control group (group B). 3 and 5 contralateral FNF were recorded respectively in group A and B. An interim analysis showed a non-effectiveness of the device therefore enrollment was suspended.

DISCUSSION:

In all group A failures a difficult positioning of the PNS was recorded: surgical techniques errors may have affected the result. Nevertheless, it is improbable to hypothesise that, without substantial modifications to the PNS design, this could significantly reduce the incidence of FNF. Considering that current pharmacological approach can achieve, at best, a marginal reduction in FNF especially in patients at high risk, complementary approaches to provide immediate prevention of hip fractures may need to be developed.

CLINICAL TRIAL PROTOCOL:

N° 263. 03 June 2008.

A BIOMECHANICAL AND THERMAL ANALYSIS FOR BONE AUGMENTATION OF THE PROXIMAL FEMUR

In this study, we aim to create and validate a Finite Element (FE) model to estimate the bone temperature after cement injection and compare the simulation temperature results with experimental data in three key locations of the proximal femur. Simulation results suggest that the maximum temperature-rise measured at the bone surface is 10°C which occurs about 12 minutes after the injection. Temperature profiles measured during the experiment showed an agreement with those of the simulation with an average error of 1.73°C Although additional experiments are required to further validate the model, results of this study suggest that this model is a promising tool for bone augmentation planning to lower the risk of thermal necrosis.

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.

EVALUATION OF A BONE REINFORCEMENT TECHNIQUE USING FINITE ELEMENT ANALYSIS

Objectives:

To compare the results of a simulated fall on the greater trochanter in the proximal portion of a synthetic femur before and after femoral reinforcement with tricalcium phosphate bone cement (TP) and polymethyl methacrylate (PMMA), using finite element analysis (FEA).

Methods:

Using two synthetic proximal femurs, a FEA simulating a fall on the greater trochanter was performed, using the Bi-directional Evolutionary Structural Optimization (BESO) program. For this analysis, the femurs were filled with TP and PMMA after perforations were created in the trochanteric region and neck. The results were compared with the strength values obtained from testing the control specimen, a synthetic bone without reinforcement.

Results:

FEA showed a value of 600 N prior to reinforcement. After cementing with PMMA, the load increased by 57.5% (945 N), and by 53% (920 N) after cementing with TP.

Conclusion:

Synthetic femurs gained resistance to fracture-causing forces in a simulated fall on the trochanter after bone reinforcement with PMMA and TP. Level of Evidence III; Experimental study.

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

BACKGROUND

High incidence and increased mortality related to secondary, contralateral proximal femoral fractures may justify invasive prophylactic augmentation that reinforces the osteoporotic proximal femur to reduce fracture risk. Bone cement-based approaches (femoroplasty) may deliver the required strengthening effect; however, the significant variation in the results of previous studies calls for a systematic analysis and optimization of this method. Our hypothesis was that efficient generalized augmentation strategies can be identified via computational optimization.

METHODS

This study investigated, by means of finite element analysis, the effect of cement location and volume on the biomechanical properties of fifteen proximal femora in sideways fall. Novel cement cloud locations were developed using the principles of bone remodeling and compared to the "single central" location that was previously reported to be optimal.

FINDINGS

The new augmentation strategies provided significantly greater biomechanical benefits compared to the "single central" cement location. Augmenting with approximately 12ml of cement in the newly identified location achieved increases of 11% in stiffness, 64% in yield force, 156% in yield energy and 59% in maximum force, on average, compared to the non-augmented state. The weaker bones experienced a greater biomechanical benefit from augmentation than stronger bones. The effect of cement volume on the biomechanical properties was approximately linear. Results of the "single central" model showed good agreement with previous experimental studies.

INTERPRETATION

These findings indicate enhanced potential of cement-based prophylactic augmentation using the newly developed cementing strategy. Future studies should determine the required level of strengthening and confirm these numerical results experimentally.

Percutaneous internal fixation with Y-STRUT® device to prevent both osteoporotic and pathological hip fractures: a prospective pilot study

Background

We studied Y-STRUT® (Hyprevention, France), a new percutaneous internal fixation device, in combination with bone cementoplasty to prevent hip fracture.

Methods

Between February 2013 and February 2015, a total of 16 femoral necks in 4 osteoporotic and 12 oncologic patients have been considered for prophylactic consolidation in this prospective multicentre pilot study involving 4 different hospitals. These consolidations were performed percutaneously under fluoroscopic guidance using Y-STRUT®, a dedicated internal fixation device. For osteoporotic patients, orthopaedic surgeons performed the prophylactic consolidations immediately after surgical treatment of a hip fracture (same anaesthesia) in the opposite side. For oncologic patients, without current hip fracture but considered at risk (Mirels score ≥8), interventional radiologists performed the procedures. We report the preliminary results of feasibility, safety and tolerance of these preventive consolidations using Y-STRUT®.

Results

Four patients (mean 83 years old) had prophylactic consolidation because of a severe osteoporosis (mean T-score −3.30) resulting in first hip fractures. Ten patients (mean 61 years old) were treated because of impending pathological fractures (mean Mirels score 9) related to femoral neck osteolytic metastases. All the procedures were performed with success. Wound healing was achieved in all cases with no access site complication. Radiographic exams performed at 3 months follow-up revealed that Y-STRUT® was well integrated in the bone. For the osteoporotic cohort, mean pain was 0.9 ± 0.7 at 3 weeks. For the oncologic cohort, it decreases from 3.6 ± 2.9 at baseline to 2.4 ± 0.9 at 2 months.

Conclusions

Preliminary results demonstrate the feasibility and safety of Y-STRUT® implantation as well as the tolerance of the device.

Prophylactic bioactive screw fixation as an alternative augmentation for femoroplasty

Femoroplasty is theoretically a prophylactic surgical procedure for femoral neck fracture. Although bone cement is generally used for augmentation, its distribution cannot be easily controlled. This study investigated whether a bioactive screw is feasible for femoroplasty as an alternative augmentation material. A mechanical test was done to compare the strength of four types of augmentation bioactive screw (Superfixsorb), two bioinert cements, or no intervention in a composite femoral bone. The peak load to fracture under simulated falling was compared among the four groups. The mean peak load to failure in the bioactive screw group (2667 N) was significantly higher than that in the intact group (2391 N) (p=0.028), comparable to that in the Simplex P cement group (2864 N) (p=0.11), and significantly lower than that of the cranioplastic cement group (3022 N) (p=0.006). The strength of a composite femur with the bioactive screw was higher than that of an intact bone and comparable to one cement augmentation. Thus, this bioactive screw can be potentially used as augmentation material for femoroplasty.

Prophylactic augmentation of the osteoporotic proximal femur-mission impossible?

The high incidence of secondary hip fractures and the associated markedly increased mortality call for preventive actions that could help to avoid these injuries. By providing immediate strengthening and not relying on patient compliance, internal prophylactic augmentation of the osteoporotic proximal femur may overcome the main limitations of systemic bone drugs and wearable protective pads. However, such a method would have to provide sufficient and reliable strengthening effect with minimal risks and side effects to justify the need of an invasive treatment. The requirements for an internal reinforcement approach are thus strict and include mechanical, biological, clinical, ethical and financial criteria. Here we first attempt to describe the properties of an ideal augmentation method. Previously published methodologies and techniques developed at our research institute, including approaches using cements, metals, other materials or combined approaches, are then reviewed and evaluated according to these aspects. We conclude that none of the discussed methodologies appears to be able to deliver a sufficiently high gain-versus-risk ratio that could justify the clinical application and thus augmentation of the osteoporotic proximal femur remains a challenge. Finally, we provide suggestions for the development and evaluation of future strategies.

Percutaneous cementoplasty for painful osteolytic distal femur metastases: a case report

Percutaneous cementoplasty has been shown to immediately restore the mechanical stability of affected bones, prevent further risk of bone fractures, and allow immediate weight bearing. It is emerging as one of the most promising procedures for patients with painful bone metastasis who are unsuitable for surgery or who show resistance to radiotherapy and/or analgesic therapies. This study aimed at describing the procedure, indications, and benefits of percutaneous cementoplasty for painful osteolytic distal femur metastases. We report the case of a painful metastatic lesion in the left distal femur secondary to non-small-cell lung cancer in a 58-year-old woman. The patient underwent percutaneous cementoplasty and experienced effective pain relief and recovery of knee function postoperatively. In addition, no perioperative complication was observed. Percutaneous cementoplasty for osteolytic distal femur metastases offers effective pain relief and restores impaired knee function. Although this method may be a safe option, larger samples of retrospective or prospective confirmation are warranted.

Prophylactic augmentation of the proximal femur: an investigation of two techniques

INTRODUCTION

Osteoporotic hip fractures are an increasing problem in an ageing population. They result in high morbidity, mortality and high socioeconomic costs. For patients with poor bone quality, prophylactic augmentation of the proximal femur might be an option for fracture prevention.

METHODS

In two groups of paired human femora the potential of limited polymethyl-methacrylate (PMMA) augmentation (11-15 ml) in a V-shape pattern and the insertion of a proximal femur nail antirotation (PFNA) blade were investigated. The testing was carried out pair wise simulating the single leg stand. The untreated femur in each pair served as control. An axial load was applied until failure. Load displacement parameters and temperature increase during the augmentation process were recorded.

RESULTS

In the PMMA group no significant difference was found between the augmented and non-augmented specimen concerning load to failure (p = 0.35) and energy to failure (p = 0.9). A median temperature increase of 9.5 °C was observed in the augmented specimen. A significant correlation was found between the amount of applied PMMA and the temperature increase (Cor. Coef. = 0.82, p = 0.042). In the PFNA group, a significant decrease of load to failure and a non-significant decrease of energy to failure were observed (p = 0.037 and p = 0.075).

CONCLUSION

Limited V-shaped PMMA augmentation and PFNA blade insertion did not show any improvement in failure load or energy to failure. Volumes of up to 15 ml PMMA did not cause a critical surface temperature increase.

Surgical prevention of femoral neck fractures in elderly osteoporotic patients. A literature review

Fragility fractures of the femur are one of the major causes of morbidity and mortality worldwide. The incidence of new contralateral hip fractures in elderly osteoporotic patients ranges from 7 to 12% within 2 years after the first fracture. Secondary prevention can be divided in: pharmacological therapy based on the prescription of anti-osteoporotic drugs with different mechanism of action and non-pharmacological therapy which is based on modification of environmental risk factors, on a healthy diet with daily supplements of calcium and vitamin D and calcium and on the use of hip protectors. Recently a new form of prevention is becoming achievable: surgical prevention; the rationale of surgical reinforcement is the need to increase the resistance of the femoral neck to the compression and distraction forces acting on it. In this paper we analyse all the experimental and "on the market" device available for the surgical prevention of femoral neck fracture.

Reducing Fracture Risk Adjacent to a Plate With an Angulated Locked End Screw

OBJECTIVES

Locking screws often are used in the treatment of osteoporotic fractures. Studies show that locking screws can increase bone stresses at the plate end, which increases the possibility of peri-implant fracture. This study evaluates whether the technique used to insert the end screw is related to the fracture tolerance adjacent to the plate.

METHODS

Twelve groups of plate constructs were evaluated using a fibular diaphyseal surrogate with mechanical properties similar to osteoporotic bone. All inboard screws were nonlocked with only the end screw fixation differing among groups. The end screws were inserted either perpendicularly to the plate or at an angle of 30 degrees for 6- and 12-hole plates. For both orientations, the end screws were inserted nonlocked, locked, or by a locked overdrilling technique, resulting in 6 groups per plate length. The perpendicular nonlocked screws represented a control group. The constructs were tested to failure in 4-point bending to determine peak load, failure energy, and stiffness.

RESULTS

All constructs failed by peri-implant fracture along a plane through the 2 cortical holes of the end screw. Compared with the control group, an angulated locked screw at the plate end significantly increased the peak bending moment and energy required to produce a fracture for both plate lengths (6-hole, P = 0.008, P < 0.001; 12-hole, P = 0.006, P < 0.001).

CONCLUSIONS

The use of an angulated locked end screw may enhance the resistance of osteoporotic bone to peri-implant fractures caused by bending forces.

A new approach to prevent contralateral hip fracture: Evaluation of the effectiveness of a fracture preventing implant

BACKGROUND

Among the millions of people suffering from a hip fracture each year, 20% may sustain a contralateral hip fracture within 5 years with an associated mortality risk increase reaching 64% in the 5 following years. In this context, we performed a biomechanical study to assess the performance of a hip fracture preventing implant.

METHODS

The implant consists of two interlocking peek rods unified with surgical cement. Numerical and biomechanical tests were performed to simulate single stance load or lateral fall. Seven pairs of femurs were selected from elderly subjects suffering from osteoporosis or osteopenia, and tested ex-vivo after implantation of the device on one side.

FINDINGS

The best position for the implant was identified by numerical simulations. The loadings until failure showed that the insertion of the implant increased significantly (P<0.05) both fracture load (+18%) and energy to fracture (+32%) of the implanted femurs in comparison with the intraindividual controls. The instrumented femur resisted the implementation of the non-instrumented femur fracture load for 30 cycles and kept its performance at the end of the cyclic loading.

INTERPRETATION

Implantation of the fracture preventing device improved both fracture load and energy to fracture when compared with intraindividual controls. This is consistent with previous biomechanical side-impact testing on pairs of femur using the same methodology. Implant insertion seems to be relevant to support multiple falls and thus, to prevent a second hip fracture in elderly patients.

Subject-specific planning of femoroplasty: an experimental verification study

The risk of osteoporotic hip fractures may be reduced by augmenting susceptible femora with acrylic polymethylmethacrylate (PMMA) bone cement. Grossly filling the proximal femur with PMMA has shown promise, but the augmented bones can suffer from thermal necrosis or cement leakage, among other side effects. We hypothesized that, using subject-specific planning and computer-assisted augmentation, we can minimize cement volume while increasing bone strength and reducing the risk of fracture. We mechanically tested eight pairs of osteoporotic femora, after augmenting one from each pair following patient-specific planning reported earlier, which optimized cement distribution and strength increase. An average of 9.5(±1.7) ml of cement was injected in the augmented set. Augmentation significantly (P<0.05) increased the yield load by 33%, maximum load by 30%, yield energy by 118%, and maximum energy by 94% relative to the non-augmented controls. Also predicted yield loads correlated well (R(2)=0.74) with the experiments and, for augmented specimens, cement profiles were predicted with an average surface error of <2 mm, further validating our simulation techniques. Results of the current study suggest that subject-specific planning of femoroplasty reduces the risk of hip fracture while minimizing the amount of cement required.

Feasibility of osteosynthesis of fractured cadaveric hips following preventive elastomer femoroplasty

BACKGROUND

In vitro cadaveric studies showed that elastomer femoroplasty prevents displacement of fracture parts after proximal hip fracture allowing for conservative treatment. In the event that secondary displacement does occur, the purpose of this present study was to determine the feasibility of performing osteosynthesis of a fractured hip after preventive treatment with elastomer femoroplasty.

METHODS

Ten pairs of human cadaveric femurs were fractured in a simulated fall configuration. From each pair, one femur was randomly selected for elastomer femoroplasty prior to fracture generation and the contralateral femur was used as control. Following hip fracture generation, osteosynthesis was performed in all femurs. The operative time per case, technical difficulties during the procedure, and postoperative energy-to-failure load were recorded.

RESULTS

The mean (SD) time to perform osteosynthesis was 20 (6) minutes in the control-group and 19 (5) minutes in the elastomer femoroplasty-group (P=0.69). During osteosynthesis of the fractured hip in the elastomer femoroplasty-group, no difficulties including the need for additional instruments to remove elastomer from the proximal femur were recorded. Postoperative energy-to-failure load was similar in the control-group and the elastomer femoroplasty-group.

CONCLUSION

Fixation with routine osteosynthesis of displaced cadaveric hip fractures is not hindered by the presence of previously injected elastomer.

Fracture prevention by prophylactic femoroplasty of the proximal femur--metallic compared with cemented augmentation

OBJECTIVES

To compare 2 different femoral neck augmentation techniques at improving the mechanical strength of the femoral neck.

METHODS

Twenty pairs of human cadaveric femora were randomly divided into 2 groups. In 1 group, the femora were augmented with a steel spiral; the other group with the cemented technique. The untreated contralateral side served as an intraindividual control. Fracture strength was evaluated using an established biomechanical testing scenario mimicking a fall on the greater trochanter (Hayes fall).

RESULTS

The peak load to failure was significantly higher in the steel spiral group (P = 0.0024) and in the cemented group (P = 0.001) compared with the intraindividual controls. The peak load to failure showed a median of 3167 N (1825-5230 N) in the spiral group and 2485 N (1066-4395 N) in the spiral control group. The peak load to failure in the cemented group was 3698 N (SD ± 1249 N) compared with 2763 N (SD ± 1335 N) in the cement control group. Furthermore, fracture displacement was clearly reduced in the steel spiral group.

CONCLUSIONS

Femoral augmentations using steel spirals or cement-based femoroplasty are technically feasible procedures. Our results demonstrate that a prophylactic reinforced proximal femur has higher strength when compared with the untreated contralateral limb. Prophylactic augmentation has potential to become an auxiliary treatment option to protect the osteoporotic proximal femur against fracture.

Subject-specific planning of femoroplasty: a combined evolutionary optimization and particle diffusion model approach

A potential effective treatment for prevention of osteoporotic hip fractures is augmentation of the mechanical properties of the femur by injecting it with agents such as (PMMA) bone cement - femoroplasty. The operation, however, is only in research stage and can benefit substantially from computer planning and optimization. We report the results of computational planning and optimization of the procedure for biomechanical evaluation. An evolutionary optimization method was used to optimally place the cement in finite element (FE) models of seven osteoporotic bone specimens. The optimization, with some inter-specimen variations, suggested that areas close to the cortex in the superior and inferior of the neck and supero-lateral aspect of the greater trochanter will benefit from augmentation. We then used a particle-based model for bone cement diffusion simulation to match the optimized pattern, taking into account the limitations of the actual surgery, including limited volume of injection to prevent thermal necrosis. Simulations showed that the yield load can be significantly increased by more than 30%, using only 9 ml of bone cement. This increase is comparable to previous literature reports where gross filling of the bone was employed instead, using more than 40 ml of cement. These findings, along with the differences in the optimized plans between specimens, emphasize the need for subject-specific models for effective planning of femoral augmentation.

Development of an animal fracture model for evaluation of cement augmentation femoroplasty: an in vitro biomechanical study

Osteoporotic hip fracture is the most severe kind of fracture with high morbidity and mortality. Patients' ambulation and quality of life are significantly affected by the fracture because only 50% regain their prefracture functional status, even if they undergo surgeries. There are many issues associated with the current preventive methods e.g., cost, side effects, patient compliance, and time for onset of action. Femoroplasty, the injection of bone cement into the proximal femur to augment femoral strength and to prevent fracture, has been an option with great potential. However, until now femoroplasty has remained at the stage of biomechanical testing. No in vivo study has evaluated its safety and effectiveness; there is not even an animal model for such investigations. The objective of this study was to develop a proximal femur fracture goat model that consistently fractures at the proximal femur when subject to vertical load, simulating osteoporotic hip fractures in human. Six pairs of fresh frozen mature Chinese goats' femora were obtained and randomly assigned into two groups. For the experimental group, a cylindrical bone defect was created at the proximal femur, while the control was left untreated. In addition, a configuration to mimic the mechanical axis of the goat femur was developed. When subjected to load along the mechanical axis, all the specimens from the bone defect group experienced femoral neck fractures, while fractures occurred at the femoral neck or other sites of the proximal femur in the control group. The biomechanical property (failure load) of the bone defect specimens was significantly lower than that of the control specimens (p<0.05). Osteoporotic hip fractures of humans were simulated by a goat fracture model, which may serve as a reference for future femoroplasty studies in vivo. The newly developed configuration simulating a femoral mechanical axis for biomechanical tests was practicable during the study.

Biomechanical analysis of impending femoral neck fractures: the role of percutaneous cement augmentation for osteolytic lesions

BACKGROUND

Management of impending pathologic femoral neck fractures includes internal fixation, arthroplasty and megaprostheses. The study aim was to determine the augmentative effect of cement injection for minimally invasive treatment of femoral neck lesions.

METHODS

Twenty-seven cadaveric femora received a simulated osteolytic lesion previously shown to decrease the femur's failure load by 50%. Specimens were allocated to three groups of nine and loaded to failure in simulated single-leg stance: (1) percutaneous cementation + internal fixation (PCIF); (2) percutaneous cementation (PC); and (3) internal fixation (IF). Lesion-only and augmented finite element models were virtually loaded and stresses were queried adjacent to the lesion.

FINDINGS

PCIF resulted in the largest failure load though the increase was not significantly greater than the PC or IF groups. Inspection of the PC and PCIF specimens indicated that the generation of a cement column that spanned the superior and inferior cortices of the femoral neck increased failure loads significantly. Finite element analysis indicated that IF and PCIF constructs decreased the stress adjacent to the lesion to intact femur levels. Cementation without superior-to-inferior femoral neck cortical contact did not restore proximal femoral stress toward the intact condition.

INTERPRETATION

Internal fixation alone and internal fixation with or without cementation produce similar levels of mechanical augmentation in femora containing a high-risk lesion of impending fracture. A cement injection technique that produces a cement column contacting the superior and inferior femoral neck cortices confers the highest degree of biomechanical stability, should percutaneous cementation alone be performed.

DXA and pQCT predict pertrochanteric and not femoral neck fracture load in a human side-impact fracture model

The validity of dual energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT) measurements as predictors of pertrochanteric and femoral neck fracture loads was compared in an experimental simulation of a fall on the greater trochanter. 65 proximal femora were harvested from patients at autopsy. All specimens were scanned with use of DXA for areal bone mineral density and pQCT for volumetric densities at selected sites of the proximal femur. A three-point bending test simulating a side-impact was performed to determine fracture load and resulted in 16 femoral neck and 49 pertrochanteric fractures. Regression analysis revealed that DXA BMD trochanter was the best variable at predicting fracture load of pertrochanteric fractures with an adjusted R(2) of 0.824 (p < 0.0001). There was no correlation between densitometric parameters and the fracture load of femoral neck fractures. A significant correlation further was found between body weight, height, femoral head diameter, and neck length on the one side and fracture load on the other side, irrespective of the fracture type. Clinically, the DXA BMD trochanter should be favored and integrated routinely as well as biometric and geometric parameters, particularly in elderly people with known osteoporosis at risk for falls.

A Particle Model for Prediction of Cement Infiltration of Cancellous Bone in Osteoporotic Bone Augmentation

Femoroplasty is a potential preventive treatment for osteoporotic hip fractures. It involves augmenting mechanical properties of the femur by injecting Polymethylmethacrylate (PMMA) bone cement. To reduce the risks involved and maximize the outcome, however, the procedure needs to be carefully planned and executed. An important part of the planning system is predicting infiltration of cement into the porous medium of cancellous bone. We used the method of Smoothed Particle Hydrodynamics (SPH) to model the flow of PMMA inside porous media. We modified the standard formulation of SPH to incorporate the extreme viscosities associated with bone cement. Darcy creeping flow of fluids through isotropic porous media was simulated and the results were compared with those reported in the literature. Further validation involved injecting PMMA cement inside porous foam blocks — osteoporotic cancellous bone surrogates — and simulating the injections using our proposed SPH model. Millimeter accuracy was obtained in comparing the simulated and actual cement shapes. Also, strong correlations were found between the simulated and the experimental data of spreading distance (R² = 0.86) and normalized pressure (R² = 0.90). Results suggest that the proposed model is suitable for use in an osteoporotic femoral augmentation planning framework.