The biomechanical effect of bone quality and fracture topography on locking plate fixation in periprosthetic femoral fractures

Failure analysis and design improvement of retrieved plates from revision surgery

Background

The fracture of bone plate can cause considerable pain for the patient and increase the burden on the public finances. This study aims to explore the failure mechanism of 49 plates retrieved from revision surgery and introduce pure magnesium (Mg) block to improve the biomechanical performance of the plate via decreasing the stiffness and to stimulate the biological response of the plate potentially by the degradation of Mg block.

Methods

The morphological analysis and component analysis of the plates were conducted to determine the fracture reason of the plates combining the clinical data. According to the structural feature, the 49 retrieved plates were divided into: traditional plate (TP), asymmetrical plate (AP), reconstructive plate (RP) and central enhancement plate (CEP), and their structure features are normalized in a commercial plate, respectively. The biomechanical performance of the plates was evaluated using a validated femoral finite element model. A block of pure Mg with a thickness of 1 mm, 1.5 mm and 2 mm was also incorporated into the CEP to be assessed.

Results

The results indicated that the retrieved plates mainly failed due to fatigue fracture induced by delayed union or nonunion (44/49), and using pure titanium plates in weight-bearing areas increased the risk of fracture compared with Ti alloy plates when the delayed union or nonunion occurred. The TP demonstrated the highest compression resistance and bending resistance, while CEP had the highest rotational resistance. As the thickness of the Mg block was increased, the stress on the plate in compression decreased, but the stress in rotation increased. The plate with a 1.5 mm Mg block demonstrated excellent compression resistance, bending resistance and rotational resistance.

Conclusion

Fatigue fracture resulting from the delayed union or nonunion is the primary failure reason of plates in clinic. The incorporation of Mg block into plate improves the biomechanical performance and has the potential to promote bone healing. The plate with a 1.5 mm Mg block may be suitable for use in orthopaedics.

The translational potential of this article

This study assessed the failure mechanism of retrieved bone plates and used this data to develop a novel plate incorporating a 1.5 mm block of pure Mg block at the position corresponding to the fracture line. The novel plate exhibited excellent compression resistance, bending resistance and rotational resistance due to the alleviation of stress concentrations. The Mg block has the potential to degrade over time to promote fracture healing and prevents fatigue fracture of plates.

Five states of reduction in OTA/AO A1.3 intertrochanteric fractures of the femur a biomechanical study

OBJECTIVE

This study aims to analyze the differences in mechanical stability of OTA/AO 31A1.3 intertrochanteric fractures under various reduction conditions.

METHODS

Twenty standard synbone artificial femur test bones were selected for the OTA/AO 31A1.3 intertrochanteric fracture model. The models were divided into five groups according to their reduction state: positive support, neutral support, negative support, varus fixation, and valgus fixation, with four specimens in each group. All models were fixed using PFNA intramedullary fixation and subjected to static axial compression tests. The subsidence displacement of the proximal femur under different loads and the axial stiffness of the model were measured to verify the mechanical stability of the OTA/AO 31A1.3 intertrochanteric fracture under different reduction conditions.

RESULTS

After the static axial compression test, the proximal femoral subsidence displacement in the positive support and neutral support groups was lower than that in the negative support, valgus fixation, and varus fixation groups (p < 0.001). The axial stiffness of the model was highest in the positive support group. Significant differences in subsidence displacement and axial stiffness were found between the groups (p < 0.001). The positive support group demonstrated the best mechanical stability, while the varus fixation group showed the poorest performance.

CONCLUSION

Positive support of the medial cortex can be regarded as the best reduction state for OTA/AO 31A1.3 intertrochanteric fractures, suggesting that this approach should be preferred during surgery to enhance mechanical stability and improve clinical outcomes. Conversely, varus fixation should be avoided due to its inferior stability.

Impact of bone health on the mechanics of plate fixation for Vancouver B1 periprosthetic femoral fractures

BACKGROUND

Condyle-spanning plate-screw constructs have shown potential to lower the risks of femoral refractures after the healing of a primary Vancouver type B1 periprosthetic femoral fracture. Limited information exists to show how osteoporosis (a risk factor for periprosthetic femoral fractures) may affect the plate fixation during activities of daily living.

METHODS

Using total hip arthroplasty and plate-implanted finite element models of three osteoporotic femurs, this study simulated physiological loads of three activities of daily living, as well as osteoporosis associated muscle weakening, and compared the calculated stress/strain, load transfer and local stiffness with experimentally validated models of three healthy femurs. Two plating systems and two construct lengths (a diaphyseal construct and a condyle-spanning construct) were modeled.

FINDINGS

Osteoporotic femurs showed higher bone strain (21.9%) and higher peak plate stress (144.3%) as compared with healthy femurs. Compared with shorter diaphyseal constructs, condyle-spanning constructs of two plating systems reduced bone strains in both healthy and osteoporotic femurs (both applying 'the normal' and 'the weakened muscle forces') around the most distal diaphyseal screw and in the distal metaphysis, both locations where secondary fractures are typically reported. The lowered resultant compressive force and the increased local compressive stiffness in the distal diaphysis and metaphysis may be associated with strain reductions via condyle-spanning constructs.

INTERPRETATION

Strain reductions in condyle-spanning constructs agreed with the clinically reported lowered risks of femoral refractures in the distal diaphysis and metaphysis. Multiple condylar screws may mitigate the concentrated strains in the lateral condyle, especially in osteoporotic femurs.

The influence of composite bone plates in Vancouver femur B1 fracture fixation after post-operative, and healed bone stages: A finite element study

Conventional stainless steel or titanium plates are used for bone fracture fixation to provide support at fracture location. Plates with high elastic modulus reduce the transfer of compressive load at the fracture location (due to stress shielding), causing failure. The objective of the study is to find for composite bone plates with different types of fibers and varied fiber orientations for post-operative (PO) and healed bone (HB) conditions which can reduce the stress shielding. Femur fracture fixation was constructed with 12 holes narrow type with metal and composite bone plates. The fracture gap was constructed with soft bone region for post-operative (PO) condition and harder bone for healed bone (HB). Composite bone plates with different configurations (fiber directions) and types (thickness and width) were analyzed to study the stress distribution and movement in the fracture location. The models were analyzed and the stresses in plate and callus, movement and strain in axial and shear direction in both metal and composite bone plates were studied. The metal and composite plates (carbon fiber/epoxy, fiberglass/epoxy, and flax/epoxy) used for most common Vancouver type B1 fracture to observe the biomechanical behavior of different models in PO and HB condition. The FE simulation on different configurations and types of composite plates provide in-depth idea about choosing the suitable composite bone plate. There are variations in behavior for varying types and configurations, but the performance of most of the plates are either better or similar to that of metal plate, except the plates with higher width.

Metal and composite bone plates for B1 periprosthetic femoral fracture in healthy and osteoporotic condition: A comparative biomechanical study

The major concern after total hip arthroplasty (THA) is the incidence of periprosthetic fracture in the weaker bone, which can lead to subsequent revision surgery. Achieving the suitable fixation without affecting the stability of the well-fixed prosthesis remains controversial. Most of the studies examined the behavior of the Periprosthetic Fracture (PF) fixation (Vancouver “B1” type) through computational and experimentation on healthy bone condition with metal plates. The aim of the present study is to analyze the influences of the metal and composite bone plate PF fixation on the axial and shear movement at the fracture site. The PF fixation constructs were modeled with medical graded stainless-steel plate (construct A), titanium plate (construct B) and carbon/epoxy composite bone plate (construct C) with 12 holes and a 4 mm fracture gap. Analysis was carried out for all the stages (stage 1—Normal bone, stage 2—THA, stage 3—Immediate Post-Operative (IPO), stage 4—Post-Operative (PO) and, stage 5—Healed Bone (HB)) under various loadings for intact and osteoporosis conditions. The results showed higher stress in cortical bone for stage 3, whereas in all the other stages lower stresses were experienced in the cortical and cancelous bone under peak load in construct C for osteoporosis model compared with other constructs. The present study suggested the construct C may be suitable for osteoporosis bone conditions.

Simplified Mechanical Tests Can Simulate Physiological Mechanics of a Fixation Construct for Periprosthetic Femoral Fractures

Plate fractures after fixation of a Vancouver Type B1 periprosthetic femoral fracture (PFF) are difficult to treat and could lead to severe disability. However, due to the lack of direct measurement of in vivo performance of the PFF fixation construct, it is unknown whether current standard mechanical tests or previous experimental and computational studies have appropriately reproduced the in vivo mechanics of the plate. To provide a basis for the evaluation and development of appropriate mechanical tests for assessment of plate fracture risk, this study applied loads of common activities of daily living (ADLs) to implanted femur finite element (FE) models with PFF fixation constructs with an existing or a healed PFF. Based on FE simulated plate mechanics, the standard four-point-bend test adequately matched the stress state and the resultant bending moment in the plate as compared with femur models with an existing PFF. In addition, the newly developed constrained three-point-bend tests were able to reproduce plate stresses in models with a healed PFF. Furthermore, a combined bending and compression cadaveric test was appropriate for risk assessment including both plate fracture and screw loosening after the complete healing of PFF. The result of this study provides the means for combined experimental and computational preclinical evaluation of PFF fixation constructs.

The impact of stem fixation method on Vancouver Type B1 periprosthetic femoral fracture management

INTRODUCTION

Our understanding of the impact of the stem fixation method in total hip arthroplasty (THA) on the subsequent management of periprosthetic femoral fractures (PFF) is still limited. This study aimed to investigate and quantify the effect of the stem fixation method, i.e., cemented vs. uncemented THA, on the management of Vancouver Type B1 periprosthetic femoral fractures with the same plate.

METHODS

Eight laboratory models of synthetic femora were divided into two groups and implanted with either a cemented or uncemented hip prosthesis. The overall stiffness and strain distribution were measured under an anatomical one-legged stance. All eight specimens underwent an osteotomy to simulate Vancouver type B1 PFF's. Fractures were then fixed using the same extramedullary plate and screws. The same measurements and fracture movement were taken under the same loading conditions.

RESULTS

Highlighted that the uncemented THA and PFF fixation constructs had a lower overall stiffness. Subsequently, the mechanical strain on the fracture plate for the uncemented construct was higher compared to the cemented constructs.

CONCLUSION

PFF fixation of a Vancouver type B1 fracture using a plate may have a higher risk of failure in uncemented THAs.

Static and dynamic examination of a locking plate in various setups for the stabilization of bone shaft fractures, including periprosthetic

Introduction: Hip and knee arthroplasty, formerly known as the “gold standard” in the treatment of articular cartilage damage, after a period of being highly popular, are changing the way they are perceived over time due to their related complications. The number of complications is directly proportional to the number of prostheses placed. This is the case of numerus arthroplasty surgeries, also involving other joints. Since there is no tissue compatibility between the metal prosthesis and the bone tissue, the former represents a negative biological element that hinders the healing of the fracture. Objective of the study: The study aims at addressing the following questions: 1. What is the elasticity of the fixation with a locking plate depending on the number of screws in both fragments, in the case of interfractural diastasis?, 2. What is the elasticity of the fixation with a locking plate depending on the number of screws in both fragments, in the case of fracture-on-fracture compression? 3. What is the difference in elasticity of the fixation using the cable system on a fracture with prosthesis?, 4. Determining the influence of different stabilization setups with the locking plate screws on the spacing of the fracture on the static and dynamic experimental model, 5. Is it possible to achieve elasticity of the stabilization stimulating bone union in a plate-based fixation, and when? Material and methods: The study was performed in the research laboratory of ChM. The subject of the study was the ChM 5.0 ChLP straight narrow compression locking plate with limited contact L-238, holes-15. The plate was mounted using ChM 3.5 locking screws: 5.0 ChLP 3.5 x 18T self-tapping screw and 5.0 ChLP 3.5 x 36T self-tapping screw. The test was carried out under static and dynamic conditions. Results and Conclusions: 1. The elasticity of the fixation with a locking plate at the interfractural diastasis is inversely proportional to the number of screws (plate deflection), 2. The elasticity of the fixation with a locking plate at the fracture-on-fracture compression is inversely proportional to the number of screws (fracture-on-fracture compression), 3. Application of the “cable system” on the fracture with prosthesis and the derotation screw optimizes the elasticity of the fixation and seems to be an optimal solution (in periprosthetic fractures), 4. Studies on the experimental static and dynamic model demonstrated that placing screws in all the openings of the plate is a restrained/clinically useless fixation. 5. The elasticity of the stabilization stimulating bone union can be obtained in the plate fixation supported by the "cable system".

Differences between proximal bone remodeling in femoral revisions for aseptic loosening and periprosthetic fractures using the Wagner SL stem

Background

Monoblock taper fluted stems have been reliably used to treat proximal femoral periprosthetic fractures (PFF) and femoral aseptic loosening (AL). Although proximal femoral remodeling has been observed around the Wagner Self-Locking (SL) stem, the exact characteristics of this process are yet to be established. Our aim was to compare the remodeling that takes place after femoral revisions for PFF and AL.

Methods

Consecutive patients between January 2015 and December 2017 undergoing femoral revision using the Wagner SL stem for PFF or AL without an extended trochanteric osteotomy (ETO) or bone grafting were selected from our database. Radiological follow-up was performed using plain antero-posterior hip radiographs taken postoperatively and at 3, 6, 12 months and at 24 months. The Global Radiological Score (GRxS) was utilized by four blinded observers. Intra and interobserver variability was calculated. Secondary outcome measures included the Oxford Hip Score and the Visual Analog Scale for pain.

Results

We identified 20 patients from our database, 10 PFF and 10 AL cases. The severity of AL was Paprosky 2 in 2 cases, Paprosky 3A in 2 cases and Paprosky 3B in 6. PFF were classified as Vancouver B2 in 7 cases and Vancouver B3 in 3 cases. Patients undergoing femoral revision for PFF regained 89% (GRxS: 17.7/20) of their bone stock by 6 months, whilst patients with AL, required almost 2 years to achieve similar reconstitution of proximal femoral bony architecture 86% (GRxS: 17.1/20). Inter-observer reproducibility for numerical GRxS values showed a “good” correlation with 0.68, whilst the intra-observer agreement was “very good” with 0.89. Except immediate after the revision, we found a significant difference between the GRxS results of the two groups at each timepoint with pair-wise comparisons. Functional results were similar in the two groups. We were not able to show a correlation between GRxS and functional results.

Conclusions

Proximal femoral bone stock reconstitutes much quicker around PFF, than in the cases of AL, where revision is performed without an ETO. The accuracy of GRxS measurements on plain radiographs showed good reproducibility, making it suitable for everyday use in a revision arthroplasty practice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04062-6.

A biomechanical study on the laminate stacking sequence in composite bone plates for vancouver femur B1 fracture fixation

BACKGROUND AND OBJECTIVES

Composite bone plates are proposed for fracture fixation in periprosthetic femoral fracture. Metallic plates, having high stiffness compared to bone lead to stress shielding, reduce the compression force in the fracture site, affectthe healing process. Reduction of stiffness in the axial direction due to above reason without lowering the stiffness in transverse to avoid much of shear strain and thus avoiding instability at the fracture site leads to selective stress shielding. This can only be achieved through meticulously designed fiber reinforced composite. In the present work varied fiber orientations in the stacked laminates with varied fiber types are employed in a post-operative femur fixation for the in-silico analyses of their effectiveness using finite element analysis.

METHODS

In this study a Total Hip Arthroplasty (THA) model is constructed with composite bone plates. Three-dimensional narrow type metal plate is modeled with 12 holes and length of 194 mm. Three different types of composite bone plates are modeled with 12 holes of different size for the analysis i.e. Type 1 (5.6 mm thickness and 16 mm width), Type 2 (6 mm thickness and 16 mm width) and Type 3(6 mm thickness and 18 mm width). Anatomical 3D FE models of THA with composite bone plates are constructed to find out the interfacial stresses and strains. The finite element software ANSYS is used to perform the analysis.

RESULTS

A three-dimensional FE model of immediately post-operative femur fixation is developed and studied the maximum stress distribution, strain and movement in axial/shear direction in the metal and composite bone plate near to the fracture site. In the present study, the metal and composite plate (carbon/epoxy, glass/epoxy and flax/epoxy) used for most common Vancouver type B1 fracture to observe the biomechanical behavior of different models in IPO condition using FEA.

CONCLUSIONS

Optimizing the fiber orientations of composite bone plates of Total Hip Arthroplasty (THA) model by controlling the biomechanical stresses could be a favorable approach. The finite element analysis approach gives a viable solution to design the composite bone plate and for designing future models that preserves the biomechanical function of THA with composite bone plate.

An experimental evaluation of fracture movement in two alternative tibial fracture fixation models using a vibrating platform

Several studies have investigated the effect of low-magnitude-high-frequency vibration on the outcome of fracture healing in animal models. The aim of this study was to quantify and compare the micromovement at the fracture gap in a tibial fracture fixed with an external fixator in both a surrogate model of a tibial fracture and a cadaver human leg under static loading, both subjected to vibration. The constructs were loaded under static axial loads of 50, 100, 150 and 200 N and then subjected to vibration at each load using a commercial vibration platform, using a DVRT sensor to quantify static and dynamic fracture movement. The overall stiffness of the cadaver leg was significantly higher than the surrogate model under static loading. This resulted in a significantly higher fracture movement in the surrogate model. Under vibration, the fracture movements induced at the fracture gap in the surrogate model and the cadaver leg were 0.024 ± 0.009 mm and 0.016 ± 0.002 mm, respectively, at 200 N loading. Soft tissues can alter the overall stiffness and fracture movement recorded in biomechanical studies investigating the effect of various devices or therapies. While the relative comparison between the devices or therapies may remain valid, absolute magnitude of recordings measured externally must be interpreted with caution.

Periprosthetic fracture fixation of the femur following total hip arthroplasty: A review of biomechanical testing - Part II

BACKGROUND

Periprosthetic femoral fracture is a severe complication of total hip arthroplasty. A previous review published in 2011 summarised the biomechanical studies regarding periprosthetic femoral fracture and its fixation techniques. Since then, there have been several commercially available fracture plates designed specifically for the treatment of these fractures. However, several clinical studies still report failure of fixation treatments used for these fractures.

METHODS

The current literature on biomechanical models of periprosthetic femoral fracture fixation since 2010 to present is reviewed. The methodologies involved in the experimental and computational studies of periprosthetic femoral fracture fixation are described and compared with particular focus on the recent developments.

FINDINGS

Several issues raised in the previous review paper have been addressed by current studies; such as validating computational results with experimental data. Current experimental studies are more sophisticated in design. Computational studies have been useful in studying fixation methods or conditions (such as bone healing) that are difficult to study in vivo or in vitro. However, a few issues still remain and are highlighted.

INTERPRETATION

The increased use of computational studies in investigating periprosthetic femoral fracture fixation techniques has proven valuable. Existing protocols for testing periprosthetic femoral fracture fixation need to be standardised in order to make more direct and conclusive comparisons between studies. A consensus on the 'optimum' treatment method for periprosthetic femoral fracture fixation needs to be achieved.

Failed osteosynthesis of cemented B1 periprosthetic fractures

BACKGROUND

Periprosthetic fractures about the hip are increasingly common. The literature estimates a failure rate of approximately 10% in Vancouver B1 type fractures which have undergone fixation. There is currently no guidance available on the next step of management for this patient group. This study presents a series of nine Vancouver B1 fractures with failed osteosynthesis and proposes that repeated fixation has poorer results than revision.

METHODS

A total of nine patients (five women, four men) with a mean age of 71.2 years (52-83) underwent operative treatment for failed osteosynthesis of periprosthetic fractures of Vancouver type B1. Three patients were revised to a long revision stem while six patients had repeated osteosythesis. Failure was defined as the need for further operative intervention.

RESULTS

The three patients revised to a long revision stem at first failure of osteosynthesis required no further surgical intervention. All six patients who had repeat osteoynthesis failed again. Five patients were subsequently successfully treated with revision of the primary stem, three were revised to a long revision stem while two patients required proximal femoral replacement. One patient died prior to revision. The mean follow up following initial B1 fracture was 49.3 months and following definitive operative intervention was 37.7 months. Six patients had died at 1st July 2017.

CONCLUSION

Failed osteosynthesis of B1 fractures may necessitate revision rather than repeat fixation, regardless of how well fixed the stem appears. Revision to a long stem provided good results in this cohort.

Finite element analysis of the femoral diaphysis of fresh-frozen cadavers with computed tomography and mechanical testing

Background

The purpose of this study was to validate a diaphyseal femoral fracture model using a finite element analysis (FEA) with mechanical testing in fresh-frozen cadavers.

Methods

We used 18 intact femora (9 right and 9 left) from 9 fresh-frozen cadavers. Specimens were obtained from 5 males and 4 females with a mean age of 85.6 years. We compared a computed tomography (CT)-based FEA model to diaphyseal femoral fracture loads and stiffness obtained by three-point bending. Four material characteristic conversion equations (the Keyak, Carter, and Keller equations plus Keller’s equation for the vertebra) with different shell thicknesses (0.3, 0.4, and 0.5 mm) were compared with the mechanical testing.

Results

The average fracture load was 4582.8 N and the mean stiffness was 942.0 N/mm from actual mechanical testing. FEA prediction using Keller’s equation for the vertebra with a 0.4-mm shell thickness showed the best correlations with the fracture load (R² = 0.76) and stiffness (R² = 0.54). Shell thicknesses of 0.3 and 0.5 mm in Keller’s equation for the vertebra also showed a strong correlation with fracture load (R² = 0.66 for both) and stiffness (R² = 0.50 and 0.52, respectively). There were no significant correlations with the other equations.

Conclusion

We validated femoral diaphyseal fracture loads and stiffness using an FEA in a cadaveric study.

A methodology for the generation and non-destructive characterisation of transverse fractures in long bones

Long bone fractures are common and although treatments are highly effective in most cases, it is challenging to achieve successful repair for groups such as open and periprosthetic fractures. Previous biomechanical studies of fracture repair, including computer and experimental models, have simplified the fracture with a flat geometry or a gap, and there is a need for a more accurate fracture representation to mimic the situation in-vivo. The aims of this study were to develop a methodology for generating repeatable transverse fractures in long bones in-vitro and to characterise the fracture surface using non-invasive computer tomography (CT) methods. Ten porcine femora were fractured in a custom-built rig under high-rate loading conditions to generate consistent transverse fractures (angle to femoral axis < 30 degrees). The bones were imaged using high resolution peripheral quantitative CT (HR-pQCT). A method was developed to extract the roughness and form profiles of the fracture surface from the image data using custom code and Guassian filters. The method was tested and validated using artificially generated waveforms. The results revealed that the smoothing algorithm used in the script was robust but the optimum kernel size has to be considered.

•

A new method to generate and quantify long bone fracture surface geometry is proposed.

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Reliable transverse fractures were generated and imaged using microCT.

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A non-destructive method to characterise the surface from the images was developed

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Validation of the method using benchmark waveforms showed the method to be robust

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By tuning the filtering conditions, specific characteristics of the surface can be extracted.

Prediction of fracture load and stiffness of the proximal femur by CT-based specimen specific finite element analysis: cadaveric validation study

Background

Finite element analysis (FEA) of the proximal femur has been previously validated with large mesh size, but these were insufficient to simulate the model with small implants in recent studies. This study aimed to validate the proximal femoral computed tomography (CT)-based specimen-specific FEA model with smaller mesh size using fresh frozen cadavers.

Methods

Twenty proximal femora from 10 cadavers (mean age, 87.1 years) were examined. CT was performed on all specimens with a calibration phantom. Nonlinear FEA prediction with stance configuration was performed using Mechanical Finder (mesh,1.5 mm tetrahedral elements; shell thickness, 0.2 mm; Poisson’s coefficient, 0.3), in comparison with mechanical testing. Force was applied at a fixed vertical displacement rate, and the magnitude of the applied load and displacement were continuously recorded. The fracture load and stiffness were calculated from force–displacement curve, and the correlation between mechanical testing and FEA prediction was examined.

Results

A pilot study with one femur revealed that the equations proposed by Keller for vertebra were the most reproducible for calculating Young’s modulus and the yield stress of elements of the proximal femur. There was a good linear correlation between fracture loads of mechanical testing and FEA prediction (R² = 0.6187) and between the stiffness of mechanical testing and FEA prediction (R² = 0.5499). There was a good linear correlation between fracture load and stiffness (R² = 0.6345) in mechanical testing and an excellent correlation between these (R² = 0.9240) in FEA prediction.

Conclusions

CT-based specimen-specific FEA model of the proximal femur with small element size was validated using fresh frozen cadavers. The equations proposed by Keller for vertebra were found to be the most reproducible for the proximal femur in elderly people.

Osteosynthesis of periprosthetic type A and B femoral fractures using an unlocked plate with integrated cerclage cable and trochanteric hook: A multicenter retrospective study of 45 patients with mean follow-up of 20 months

INTRODUCTION

Femoral periprosthetic fracture (FPF) is a frequent complication in dependent elderly persons, with a limited life expectancy. Their management is difficult and the choice between osteosynthesis and prosthesis is still matter of discussion. To date, there is no study on unlocked plate with integrated cerclage cable and trochanteric hook for this indication. The objectives of this study were to analyze fracture healing, complication rate and functional outcome. Our hypothesis is that this technique allows a high rate of consolidation and a return to the previous state in terms of autonomy and place of residence.

MATERIALS AND METHODS

We conducted a retrospective multicenter study between 2010 and 2015. The inclusion criteria were: patients with type A and B FPF according to the classification of Vancouver who received osteosynthesis hook plate. The evaluation focused on the consolidation period, complications and pre and postoperative Parker and Katz scores. Death, nonunion, dislocation, infection and failure of fixation were considered major complications.

RESULTS

Forty-five patients met the inclusion criteria and were evaluated at mean 20 months (6-72). All fractures consolidated at a mean 7 weeks (6-10), except one that has not undergone further surgery in the absence of functional impairment. Parker score decreased from 6.4 to 4.9 (p=0.03) and Katz score from 4.8 to 4.3 (p=0.045). Five patients died within the year of the operation. Five patients living at home preoperatively were admitted to an institution, the others returned to their retirement home or nursing home.

CONCLUSION

This plate allows for a quick and effective management of patients with FPF. The low rate of complications and the very good consolidation rate lead us to use the same plate even for class B2 or B3 fractures in some patients with precarious health condition who cannot tolerate major revision surgery: Elderly, ASA score >3, loss of autonomy, Katz score <4.

Hip revision arthroplasty for failed osteosynthesis in periprosthetic Vancouver type B1 fractures using a cementless, modular, tapered revision stem

Aims

To evaluate the hypothesis that failed osteosynthesis of periprosthetic Vancouver type B1 fractures can be treated successfully with stem revision using a transfemoral approach and a cementless, modular, tapered revision stem with reproducible rates of fracture healing, stability of the revision stem, and clinically good results.

Patients and Methods

A total of 14 patients (11 women, three men) with a mean age of 72.4 years (65 to 90) undergoing revision hip arthroplasty after failed osteosynthesis of periprosthetic fractures of Vancouver type B1 were treated using a transfemoral approach to remove the well-fixed stem before insertion of a modular, fluted titanium stem which obtained distal fixation. These patients were clinically and radiologically followed up for a mean 52.2 months (24 to 144).

Results

After a mean of 15.5 weeks (standard deviation (sd) 5.7) all fractures had healed. No stems subsided and bony-ingrowth fixation had occurred according to the classification of Engh et al. The mean Harris Hip Score increased from a pre-operative score of 22.2 points (sd 9.7) to 81.5 points (sd 16.8) 24 months post-operatively. All hips had obtained an excellent result according to the classification of Beals and Tower.

Conclusions

The technique described here for stem revision provides reproducibly good results in the treatment of failed osteosynthesis for Vancouver types B1 periprosthetic fractures of the hip. Cite this article: Bone Joint J 2017;99-B(4 Supple B):11–16.

Is immediate weight bearing safe for periprosthetic distal femur fractures treated by locked plating? A feasibility study in 52 consecutive patients

Background

Periprosthetic distal femur fractures associated with total knee replacement are increasing in incidence. We hypothesized that a standardized management protocol would result in few implant failures and a low rate of postoperative complications.

Methods

Retrospective observational cohort study at an urban level 1 trauma center and academic level 2 trauma center. Consecutive patients with periprosthetic distal femur fractures and stable total knee arthroplasty were included between January 1, 2011 and December 31, 2014. Patients were managed by a standardized protocol of co-management by a hospitalist service, fracture fixation within 24 h of admission by less-invasive locked bridge plating, and immediate unrestricted postoperative weight bearing. The primary outcome measure was the rate of postoperative complications. Secondary outcome measures included time to surgery, intraoperative blood loss, duration of surgery, length of hospital stay, time to full weight bearing, and time to radiographic fracture healing.

Results

Fifty four fractures were treated in 52 patients. There were three implant failures, one deep infection, one nonunion and two patients with symptomatic malunion. One patient had knee pain due to patellar component instability associated with valgus alignment. There were ten thromboembolic complications despite consistent anticoagulation. Two patients died within 12 months of injury. Thirty-eight patients had returned to their pre-injury ambulation status at 1 year follow-up.

Conclusion

A standardized approach of less-invasive locked plating fixation and immediate unrestricted weight bearing appears safe and feasible in the management of this vulnerable patient cohort.

Trial registration number

This is a retrospective observational study without a Trial registration number.

Revision Arthroplasty Using a MUTARS® Prosthesis in Comminuted Periprosthetic Fracture of the Distal Femur

Periprosthetic fractures after total knee arthroplasty (TKA) are gradually increasing, reflecting extended lifespan, osteoporosis, and the increasing proportion of the elderly during the past decade. Supracondylar periprosthetic femoral fracture is a potential complication after TKA. Generally, open reduction and internal fixation are the conventional option for periprosthetic fracture after TKA. However, the presence of severe comminution with component loosening can cause failure of internal fixation. Although the current concept for periprosthetic fracture is open reduction and internal fixation, we introduce an unusual case of revision arthroplasty using a MUTARS® prosthesis for a comminuted periprosthetic fracture in the distal femur after TKA, with technical tips.

Application of Far Cortical Locking Technology in Periprosthetic Femoral Fracture Fixation: A Biomechanical Study

BACKGROUND

Lack of fracture movement could be a potential cause of periprosthetic femoral fracture (PFF) fixation failures. This study aimed to test whether the use of distal far cortical locking screws reduces the overall stiffness of PFF fixations and allows an increase in fracture movement compared to standard locking screws while retaining the overall strength of the PFF fixations.

METHODS

Twelve laboratory models of Vancouver type B1 PFFs were developed. In all specimens, the proximal screw fixations were similar, whereas in 6 specimens, distal locking screws were used, and in the other six specimens, far cortical locking screws. The overall stiffness, fracture movement, and pattern of strain distribution on the plate were measured in stable and unstable fractures under anatomic 1-legged stance. Specimens with unstable fracture were loaded to failure.

RESULTS

No statistical difference was found between the stiffness and fracture movement of the two groups in stable fractures. In the unstable fractures, the overall stiffness and fracture movement of the locking group was significantly higher and lower than the far cortical group, respectively. Maximum principal strain on the plate was consistently lower in the far cortical group, and there was no significant difference between the failure loads of the 2 groups.

CONCLUSION

The results indicate that far cortical locking screws can reduce the overall effective stiffness of the locking plates and increase the fracture movement while maintaining the overall strength of the PFF fixation construct. However, in unstable fractures, alternative fixation methods, for example, long stem revision might be a better option.

Managing Vancouver B1 fractures by cerclage system compared to locking plate fixation - a biomechanical study

With increasing life expectancy and number of total hip arthroplasties (THA), the need for revision surgery is increasing too. The aim of this study was to evaluate the optimal fracture treatment for a clinically characteristic Vancouver B1 fracture. We hypothesized that locking plate fixation has biomechanical advantages over fixation with a simple cerclage system. Additionally, we hypothesized that removal of the primary short stem and revision with a long stem would show biomechanical benefit. The biomechanical testing was performed with a static and a dynamic loading protocol on twenty 4th Generation sawbones. These were divided into four different groups (n = 5 each). In group 1, the primary uncemented short stem remained and the fracture was stabilized with a locking plate. In group 2, the primary stem remained and the fracture was stabilized with a cerclage stabilization system containing two stabilizers and four cerclages. In group 3, the primary stem was replaced by an uncemented long revision stem and the fracture was fixed with a locking plate. In group 4, the short stem was replaced by a long revision stem and the fracture was fixed with the cerclage system. Static testing revealed that the revision of the short stem with the long stem caused a 2-fold (p < 0.001, ANOVA) increase of axial stiffness. In dynamic testing, the number of cycles to failure was 4 times (p < 0.001, ANOVA) higher with the long revision stem. Compared to locked plating cerclage wiring demonstrated a 26% more cycles to failure (p = 0.031, ANOVA). The load to failure was 91% larger (p < 0.001, ANOVA) with the long revision stem and 11% smaller with locked plating (p < 0.001, ANOVA). In conclusion, the present biomechanical study indicates that periprosthetic Vancouver B1 fractures can be sufficiently fixed by simple cerclage systems. Revision with a long replacement stem provides a superior mechanical stability regardless of type of osteosynthesis fixation and is therefore a viable method in Vancouver B1 cases. A disadvantage of the cerclage system compared to plating is that an increased subsidence of the short stem was observed.

Periprosthetic fracture fixation in osteoporotic bone

Fixation techniques of periprosthetic fractures are far from ideal although the number of this entity is rising. The presence of an intramedullary implant generates its own fracture characteristics since stiffness is altered along the bone shaft and certain implant combinations affect load resistance of the bone. Influencing factors are cement fixation of the implant, intramedullary locking and extramedullary or intramedullary localization of the implant and the cortical thickness of the surrounding bone. Cerclage wires are ideally suited to fix radially displaced fragments around an intramedullary implant but they are susceptible to axial and torsional load. Screws should be added if these forces have to be neutralized. Stability of the screw fixation itself can be enhanced by embracement configuration around the intramedullary implant. Poor bone stock quality, often being present in metaphyseal areas limits screw fixation. Cement augmentation is an attractive option in this field to enhance screw purchase.

Peri-implant failure in dual plating of the distal humerus-A biomechanical analysis with regard to screw and plate positioning

PURPOSE

The aim of this biomechanical study was to analyse the influence of plate and screw positioning on peri-implant failure in dual plate osteosynthesis. We hypothesized that screw positioning rather than plate configuration influences the risk of peri-implant fractures.

METHODS

Twenty macerated humerus specimens were available. 5 groups of 4 were built according to specimen size. Locking dual plates (Medartis, Switzerland) were randomly applied to the distal humerus of the specimens in 4 types of configuration: Bending forces were applied using a universal testing machine until peri-implant fracture occurred.

RESULTS

Mean failure loads for respective configuration types were as follows: P1: 428.7 (±84.2) N, A1: 410.0 (±54.7) N, A0: 297.8 (±48.3) N, P0: 261.0 (±65.0) N. Configurations with positioning of the most proximal screws at different levels (P1, A1) reached significantly higher failure loads when compared to screw placement at the same level (P0, A0) (0.01≤p≤0.03). Altering the plate configuration did not significantly influence failure loads (0.34≤p≤0.58).

CONCLUSIONS

The results of this study suggest that placement of the most proximal screws rather than the configuration of the plates is critical regarding the predetermined risk of peri-implant failure in dual plate osteosynthesis of the distal humerus. Varying levels of the outermost screws of corresponding double plates seem to be crucial to avoid complications related to the osteosynthesis.

Semi-rigid screws provide an auxiliary option to plate working length to control interfragmentary movement in locking plate fixation at the distal femur

BACKGROUND

Extent and orientation of interfragmentary movement (IFM) are crucially affecting course and quality of fracture healing. The effect of different configurations for implant fixation on successful fracture healing remain unclear. We hypothesize that screw type and configuration of locking plate fixation profoundly influences stiffness and IFM for a given load in a distal femur fracture model.

METHODS

Simple analytical models are presented to elucidate the influence of fixation configuration on construct stiffness. Models were refined with a consistent single-patient-data-set to create finite-element femur models. Locking plate fixation of a distal femoral 10mm-osteotomy (comminution model) was fitted with rigid locking screws (rLS) or semi-rigid locking screws (sLS). Systematic variations of screw placements in the proximal fragment were tested. IFM was quantitatively assessed and compared for different screw placements and screw types.

RESULTS

Different screw allocations significantly affect IFM in a locking plate construct. LS placement of the first screw proximal to the fracture (plate working length, PWL) has a significant effect on axial IFM (p < 0.001). Replacing rLS with sLS caused an increase (p < 0.001) of IFM under the plate (cis-cortex) between +8.4% and +28.1% for the tested configurations but remained constant medially (<1.1%, trans-cortex). Resultant shear movements markedly increased at fracture level (p < 0.001) to the extent that plate working length increased. The ratio of shear/axial IFM was found to enhance for longer PWL. sLS versus rLS lead to significantly smaller ratios of shear/axial IFM at the cis-cortex for PWL of ≥ 62 mm (p ≤ 0.003).

CONCLUSION

Mechanical frame conditions can be significantly influenced by type and placement of the screws in locking plate osteosynthesis of the distal femur. By varying plate working length stiffness and IFM are modulated. Moderate axial and concomitantly low shear IFM could not be achieved through changes in screw placement alone. In the present transverse osteotomy model, ratio of shear/axial IFM with simultaneous moderate axial IFM is optimized by the use of appropriate plate working length of about 42-62 mm. Fixation with sLS demonstrated significantly more axial IFM underneath the plate and may further contribute to compensation of asymmetric straining.

Enhancement of hip fracture healing in the elderly: Evidence deriving from a pilot randomized trial

Enhancement of healing of osteoporotic fractures remains a significant objective of contemporary clinical care. Aiming to produce preliminary clinical evidence on the effect of antiosteoporotic drugs on the process of fragility fracture healing, a pilot prospective randomized assessor-blinded trial was performed. The tested hypothesis was that it is possible to accelerate the healing of hip fractures in the presence of osteoporosis with the administration of therapeutic agents. However, significant difficulties of recruitment and completion of follow up did not allow the researchers to produce the preliminary evidence testing the study hypothesis, highlighting the challenges that contemporary clinical investigators face when conducting studies focusing on elderly patients, with high proportion of coinciding factors affecting patients' eligibility, compliance, and overall outcome. Nevertheless, the significance of enhancing bone healing in this specific patient population, dictates further clinical efforts and future well designed and funded trials of adequate power and level of evidence are desirable to allow the effective and safer management of the consequences of the modern epidemic of osteoporosis.