Femoral Neck Fracture Model Research Articles

Biomechanical comparison of Kangli hollow screws with sliding compression locking plate system and conventional cannulated lag screws for fixation of type Pauwels III femoral neck fracture

Objective To compare the biomechanical performance of Kangli hollow screws with sliding compression locking plate system (KHS) and conventional cannulated lag screws for fixation of type Pauwels III femoral neck fracture. Methods 7 cadaveric femurs were selected, vertical fractures (Pauwels III fracture, at 70° to the horizontal) were artificially conducted in these cadaveric proximal femurs by an orthopaedic surgeon and fixed by KHS screws with plate system or conventional cannulated lag screws. Samples were positioned at 75° of the femoral shaft to the horizontal, embedded in the mould and fixed in the experimental console. Optical sensors were set at the femoral neck around the osteotomy line. Then the loading were input in the vertical, horizontal lateral direction and rotating direction around the femoral neck axis, the maximal and minimal values between the fractured fragments and the corresponding values of the loading were recorded. The values of stiffness in three directions were calculated and compared. The CT data of the left femur of a 25 year-old healthy male volunteer was input into the corresponding software and vertical femoral neck fracture model was generated. Two finite element analysis models were obtained after the fracture being fixed using these two different implants, and the Von Mises stress distribution on the femur, implants and the interface between the fractured fragments and the relative motion between the fractured fragments were compared. Results In the vertical, horizontal lateral direction and rotating direction around the femoral neck axis, the stiffness of the KHS were 3 904±1 148 N/mm, 4 324±1 234 N/mm and 11.45±4.95 N·m/° respectively, higher than those of the CSs method with the values of 3 020±1 150 N/mm, 3 020±854 N/mm and 6.53±4.83 N·m/° respectively. The differences between the two groups were statistically significant (t=2.7194, 4.7694 and 2.9424; P=0.0347, 0.0050 and 0.0423). In the finite element analysis test, the maximal Von Mises stress values distributing on the femur and the screws in the KHS group were 40.1 MPa and 126.4 MPa, and those in the CSs group were 98.1 MPa and 145.5 MPa respectively, and both values of the former were lower than the latter. But the Von Mises stress value on the interface between the fractured fragments in the KHS group was 14.37 MPa, which was much higher than that in the CSs groupwhich was 9.39 MPa. The gap at the fracture site of the CSs fixation model was dramatically larger than that of KHS fixation model. Conclusion The KHS screws and plate system could provide better immobilization effect for vertical femoral neck fracture compared to the cannulated lag screws. The risk of the screws failure was lower and the fracture union would be easier to obtained by the fixation of KHS screws with plate system. Key words: Femoral neck fractures; Fracture fixation, internal; Biomechanics; Finite element analysis

Correction: The treatment of femoral neck fracture using VEGF-loaded nanographene coated internal fixation screws.

[This corrects the article DOI: 10.1371/journal.pone.0187447.].

The biomechanical effects of femoral neck shortening on femoral head and neck

Objective Using finite element analysis to study how the biomechanics of femoral head and neck changes after neck shortening, and discuss the mechanism of obvious higher osteonecrosis of the femoral head (ONFH) rate in femoral neck shortening cases. Methods MIMICS was used to build three femoral neck fracture models with Pauwells angle of 70 degrees. The neck lengths of the three models respectively were normal, 2.5 mm shortened and 5.0 mm shortened. Every model was assembled with 3 hollow screws, and imported into the finite element analysis software ABAQUS. The stress change of femoral head and neck was analyzed by loading and restraint. Results When the femoral neck length was normal, 2.5 mm shortened and 5.0 mm shortened, the maximal tensile stress of hollow screws in upper part of the femoral neck was 15.7, 14.1 and 12.4 mPa, and the compressive stress of lower part of femoral neck was 20.2, 19.1 and 17.8 mPa, respectively. Meanwhile, the high stress bearing district was transfered to right above the femoral head from its superior lateral quadrant, and the maximum stress of non-main stress bearing district was 10.6, 12.8 and 17.2 mPa respectively. Conclusion The femoral neck shortening reduces the proximal femoral eccentricity. It doesn’t affect the stabilities of internal fixation and fracture ends, but it transfers the stress bearing district of femoral head and causes the forming of high stress bearing district in non-main stress bearing district. Key words: Femoral neck fracture; Femoral neck shortening; Biomechanics

The treatment of femoral neck fracture using VEGF-loaded nanographene coated internal fixation screws.

PurposePrevious studies have proved that vascular endothelial growth factor (VEGF) has a dual role in the promotion of new bone formation and blood vessel repair during fracture healing. However, how to introduce VEGF to a fracture site safely and effectively is still a challenge. This study aimed to prepare a VEGF-loaded nanographene coated internal fixation screw and to evaluate its effects in the treatment of femoral neck fracture.MethodsNanographene coated screws were prepared by direct liquid-phase exfoliation of the graphite method, and the surface characteristics were observed through scanning electron microscopy (SEM). VEGF was loaded on nanographene coatings through physical adsorption, and the VEGF controlled release was examined by ELISA. Then a canine femoral neck fracture model was built to examine both the angiogenic and osteogenic properties of the VEGF-loaded coated screws. X-ray, micro-CT-based microangiography, and histopathologic evaluation were used to assess the fracture healing progress.ResultsThe results demonstrated that nanographene could load VEGF effectively, and the accumulative release of VEGF clearly increased during the entire testing period (9 days) without burst release. In canine fracture models, the results of X-ray, microangiography, and histopathologic examination proved that the speed of fracture healing, new bone formation area, and revascularization of the fractured femoral heads in the VEGF-loaded coated screws groups were significantly higher than in the control groups.ConclusionOur study proved that VEGF-loaded nanographene coated screws were effective in the treatment of femoral neck fracture and prevention of avascular necrosis of femoral head.

Internal fixation of femoral neck fracture using screws coated with vascular endothelial growth factorloaded nanographene

Objective To evaluate the internal fixation screws coated with vascular endothelial growth factor (VEGF)-loaded nanographene in the treatment of femoral neck fracture. Methods Screws with nanographene coating were prepared by direct liquidphase exfoliation of the graphite. After the surface characteristics were observed through scanning electron microscopy (SEM), the nanographene coating was loaded with VEGF through physical adsorption and controlled release of the VEGF was examined by ELISA. Femoral neck fracture models were built in 10 healthy adult canines to examine both the angiogenic and osteogenic properties of the screws coated with VEGF-loaded nanographene which were implanted at the experimental sides while the screws with mere nanographene coating at the contralateral sides as controls. X-ray and histopathologic evaluations were used to assess the fracture healing progress. Results SEM demonstrated that the screws were coated successfully with VEGF-loaded nanographene. The coating did not increase the cytotoxity of screws. The accumulative release of VEGF clearly increased during the entire testing period (9 days) with a maximum release of 9.51±0.23 ng. X-ray and histopathologic examination proved better fracture healing at the experimental sides than at the contralateral sides. The percentage of trabecular area at the experimental sides (50.8%±3.3%) was insignificantly larger than at the control sides (43.7%±3.9%), and the trabecular width at the experimental sides (146.8±19.5 μm) was insignificantly greater than at the control sides (129.0±10.2 μm) (P>0.05). The area of new bone trabecula at the experimental sides (17.3%±1.5%) was significantly larger than at the control sides (8.3%±1.6%), and the microvessel density (MVD) at the experimental sides (113.4±12.5) was also significantly greater than at the control sides (61.2±9.4) (P<0.05). Conclusions The nanographene coating can load and release VEGF effectively. The screws coated with VEGF-loaded nanographene possess a certain degree of bioactivity which may promote vascular repair in the treatment of femoral neck fracture. Key words: Femoral neck fractures; Fracture fixation, internal; Bone nails; Nanocomposites; Vascular endothelial growth factor

Cannulated compression screw versus dynamic hip screw-blade in the treatment of femoral neck fractures

Objective To compare the curative effect and biomechanical performance of cannulated compression screw (CCS) and dynamic hip screw-blade (DHS-B) in the treatment of patients with femoral neck fracture.Methods Between February 2010 and February 2014,102 patients with femoral neck fracture were treated with CCS or DHS-B at our department.They were 54 males and 48 females,aged from 15 to 86 years.There were 30 subcapital fractures,51 transcervical ones and 21 base ones.CCS was used in 60 patients and DHS-B in 42.In-hospital data were collected retrospectively to compare the curative effects in 2 groups.Furthermore,femoral neck fracture models were established using 12 adult cadaveric femoral specimens.The 12 models were randomized into 2 equal groups (n =6).Group A was subjected to fixation by 3 CCSs and group B to fixation by DHS-B.The 2 groups were compared in terms of axial loading test,rotation test and destructive axial loading test.Results The operation time (59.4 ± 20.2 min),incision size (4.1 ±0.6 cm) and intraoperative blood loss (25.9 ±9.9 mL) in the CCS group were significantly less than those in the DHS-B group (88.6±22.9 min,12.1 ±1.2cmand 156.7±107.1 mL) (P ＜0.05).The Harris hip score for the DHS-B group (91.9±9.8) was significantly higher than that for the CCS group (87.2 ± 9.2) (P ＜ 0.05).There were no significant differences between the 2 groups in hospital stay,partial weight-bearing time,or postoperative complications (P ＞ 0.05).At 500 N vertical loading,the stress values at both medial and lateral sides of the femur in group A were significantly smaller than those in group B (P ＜ 0.05).There were no significant differences between groups A and B in the average sinking displacement of femoral head or the torque at a torsion angle of 6° (P ＞ 0.05).The maximum load in group A (2,135 ±120 N) was significantly smaller than that in group B (2,986 ± 98 N) (P ＜ 0.05).Conclusion In treatment of femoral neck fracture,DHS-B fixation is obviously superior to CCS fixation,because the former is in better agreement with the femoral biomechanical property,and performs better in anti-rotation and anti-compression,leading to better functional recovery of the affected hip.

The Problem of Fracture Fixation Augmentation and Description of a Novel Technique and Implant for Femoral Neck Stabilization

Fracture augmentation for osteopenic bone is a widely accepted concept but not commonly used due to the difficulty with application of the materials in conjunction with surgical implants in fracture repair. Until recently there was little choice of materials for augmentation, but new formulations of structural orthobiological matrix (SOM) have been developed, which have better flow and setting properties than the original polymethylmethacrylate and calcium phosphate ceramics materials. In addition, a new class of injectable implants with the ability to deliver some of these newer SOMs has been designed and received regulatory clearance as fracture fixation devices. This cadaveric study was undertaken to assess the feasibility of using the N-Force Fixation System in a femoral neck fracture model with 6 different SOMs. A new property of SOM was discovered regarding the flow characteristics of the tested materials within the proximal femur. Intrusion and extrusion characteristics were observed and were SOM specific. C-arm fluoroscopy and CT studies revealed the ability of intrusion-type SOM to intrude into cancellous bone trabeculae and minimize the chance of joint extrusion through fracture lines, whereas extrusion-type SOM would not intrude into trabecular spaces and demonstrated a tendency for fracture site extrusion and fracture contact interposition, risking compromise of fracture healing and angiogenesis. The instrumentation and implants gave reproducible implant placement and SOM delivery with low-pressure application and circumferential augmentation from the near cortex extending into the femoral neck and head in a tapering cone-type pattern.

Improvement in angiogenesis and osteogenesis with modified cannulated screws combined with VEGF/PLGA/fibrin glue in femoral neck fractures

Angiogenesis is essential for bone healing. Vascular endothelial growth factor (VEGF) is regarded as one of the most potent antigenic cytokines; however, there have been very few studies that have previously investigated the effects of VEGF on bone healing in a femoral neck fracture model. Thus, the aim of the present study was to test both the angiogenic and osteogenic properties of a VEGF/poly-lactic acid glycolic acid (PLGA) delivery system for the treatment of femoral neck fractures. VEGF/PLGA microspheres were prepared by the double emulsion solvent-evaporation method and in vitro VEGF release was quantified by an ELISA assay. Then the preparation of femoral neck fracture model and internal fixation were performed, and the effect of the VEGF/PLGA microspheres on bone healing was determined by X-ray, radionuclide bone scanning, and histomorphometric evaluation. The release of VEGF from the VEGF/PLGA microspheres was sustained for at least 42 days in vitro, and suspension of the delivery system in fibrin glue further slowed this VEGF release rate. In dogs, revascularization of the fractured femoral heads was significantly improved by a local injection of VEGF/PLGA/fibrin glue, and the quality and speed of fracture healing were significantly improved in the Experimental group than in the Control group. Our study confirmed that the VEGF/PLGA delivery system offers good angiogenic and osteogenic properties for the treatment of canine femoral neck fractures.

Fracture mechanics of the femoral neck in a composite bone model: Effects of platen geometry

Load applicator (platen) geometry used for axial load to failure testing of the femoral neck varies between studies and the biomechanical consequences are unknown. The purpose of this study was to determine if load application with a flat versus a conical platen results in differing fracture mechanics. Femurs were aligned in 25° of adduction and an axial compressive force was applied to the femoral heads at a rate of 6mm/min until failure. Load application with the conical platen resulted in an average ultimate failure load, stiffness, and energy to failure of 9067N, 4033N/mm, and 12.12J, respectively. Load application with the flat platen resulted in a significant (p<0.05) reduction in ultimate failure load (7620N) and stiffness (2924N/mm). Energy to failure (12.30J) was not significantly different (p=0.893). Different fracture patterns were observed for the two platens and the conical platen produced fractures more similar to clinical observations. Use of a flat platen underestimates the strength and stiffness of the femoral neck and inaccurately predicts the associated fracture pattern. These findings must be considered when interpreting the results of prior biomechanical studies on femoral neck fracture and for the development of future femoral neck fracture models.

Does a trochanteric lag screw improve fixation of vertically oriented femoral neck fractures? A biomechanical analysis in cadaveric bone

BackgroundWe assessed the biomechanical performances of a trochanteric lag screw construct and a traditional inverted triangle construct in the treatment of simulated Pauwels type 3 femoral neck fractures. MethodsAn inverted triangle construct (three 7.3-mm cannulated screws placed in inverted triangle orientation) and a trochanteric lag screw construct (two 7.3-mm cannulated screws placed across the superior portion of the femoral neck and one 4.5-mm lag screw placed perpendicular to the fracture in superolateral to inferomedial orientation) were tested in nine matched pairs of non-osteoporotic human cadaveric femora. We used a previously described vertically oriented femoral neck fracture model and testing protocol that incrementally loaded the constructs along the mechanical axis of the femur to 1400N. Specimens that survived incremental loading underwent cyclic loading. Apparent construct stiffness, force at 3mm of displacement, and survival of incremental loading were recorded. FindingsThe trochanteric lag screw group had a 70% increase in stiffness (261N/mm [29 standard deviation] versus 153N/mm [16 standard deviation]; P=0.026) and a 43% increase in force required for displacement (620N versus 435N; P=0.018) compared with the inverted triangle group. One trochanteric lag screw and no inverted triangle specimen survived incremental loading. InterpretationA trochanteric lag screw construct applied to vertically oriented femoral neck fractures provides marked improvement in mechanical performance compared with the inverted triangle construct.

THE BIOMECHANICAL EFFECTS OF DIFFERENT INTERNAL FIXATIONS IN THE TREATMENT OF FEMORAL NECK FRACTURES

The objective of this study was to contrast the biomechanical effects of standard internal fixations for femoral neck fracture treatment and provide a theoretical basis for the selection of the ideal internal fixation in the clinic.Twelve artificial PMMA femoral models were selected, and the central necks of the specimens were sawn with a electric saw at Pauwels angle of 70° to form an adduction-type femoral neck fracture model. After anatomic reduction, we fixed the specimens respectively with the DHS, three hollow screws, PFN, and dynamic sleeve three-wing screw according to the operative approach. Instron-8874 servo-hydraulic mechanical testing machine was used to fix the specimens which simulated uniped standing. We selected 15 key points on the proximal femur as test points and gave the model gradation loading at the rate of 10 mm/min with linear load 0 ~ 1200 N. The strain of each point under 1200 N load, head sink displacement under different loads, and the strain of eight points on principal pressure side were measured.A peak was observed at the eight resistance strain gages at 1200 N load, with the strain values of the DHS, three hollow screws, PFN, and dynamic sleeve three-wing screw were (-700 ± 35), (-756 ± 14), (-1362 ± 136), and (3024 ± 127) με, showing statistical significance (P &lt; 0.01). Under the same load, the head sink displacement in the group with the dynamic sleeve three-wing screw was greater than the hollow screws and PFN groups (P &lt; 0.01), but smaller than the DHS group (P &lt; 0.01). The strain values at the eight resistance strain gages in the group with the dynamic sleeve three-wing screw was larger than the other three groups under the same load, showing statistical significance (P &lt; 0.01), and the strain values demonstrated an increasing trend with the increase of load at the same fixation group.The dynamic sleeve three-wing screw has good biomechanical stability for the treatment of femoral neck fractures, which can be applied in clinical practice.

Development of self-locking cannulated compression anti-rotation blade for treatment of femoral neck fractures

Objective To develop self-locking cannulated compression anti-rotation blade and investigate its design characteristic and manipulation techniques. Methods Femoral neck fracture model was made by osteotomy on seven cadaver femurs and then fixed by self-locking cannulated compres-sion anti-rotation blade under fluoroscopic guidance according to designed procedures. After fixation, bio-mechanic test was performed to evaluate fixation stability. Results Cannulated self-locking compres-sion anti-rotation blade was tightly impacted in proximal femur and compression detected during the process of locking, with successful manipulation and stable fixation. Conclusion Because of advanced design characteristic and simple manipulation, self-locking cannulated compression anti-rotation blade can be a substitute for cannulated cancellous lag screw in treatment of femoral neck fractures. Key words: Femoral neck fractures: Fracture fixation, internal; Biomechanies

Is a helical shaped implant a superior alternative to the Dynamic Hip Screw for unstable femoral neck fractures? A biomechanical investigation

Background The Dynamic Hip Screw is well established for the treatment of femoral neck fractures. However, cut-out occurs in 1–6% of all cases. This study compared the biomechanical performance of a helical shaped implant (DHS-Blade) to the Dynamic Hip Screw in an unstable femoral neck fracture model. Methods Ten pairs of human cadaveric femora were either instrumented with a DHS-Blade or a Dynamic Hip Screw. Osteotomies were created using a custom-made saw-guide. Cyclic loading was performed by introducing in vivo measured load-trajectories to the femoral head. Starting at 1500 N, the load was stepwise increased until failure of the construct. Radiographs were taken in 5000 cycles increments to identify onset of femoral head migration with respect to the implant. A survival analysis was performed on the cycles to onset of migration. A paired t-test was carried out on the displacements of the femoral head relative to the shaft as determined by optical motion tracking. Findings One hundred percent migrations occurred for the Dynamic Hip Screw compared to 50% for the DHS-Blade. The survival probability in terms of implant anchorage was found higher for the blade ( P = 0.023). However, significant higher deformation of the repair construct was observed for the DHS-Blade ( P = 0.004). Interpretation The study showed superior implant anchorage of the DHS-Blade compared to the DHS, which might reduce the cut-out risk. Nevertheless, the blade allowed higher deformation of the femur mainly resulting in shortening of the neck, which might be due to a systematic loss of fracture reduction.

A femoral neck fracture model in rabbits

A technique was developed to create a reproducible femoral neck fracture in vitro using 5-month-old JW/CSK series male rabbits. Force attenuation of a newly developed damping material was also evaluated using this model. Ten pairs of the femora with smaller deviations in length and weight were harvested and cleaned of soft tissue. Either a right or left of each pair of the specimens was randomly selected and put into either the control or the experimental group, both of which contained equal numbers of the right and left femora. The specimens were attached to an L-shaped plate and embedded in a resin from the proximal diaphysis to the distal end so as to maintain a consistent position of the femora. They were mounted and fixed on a pedestal slanted in the coronal plane at 20°. The impact load testing was conducted using an impact mallet dropped from a height of 3 cm. The impact load was applied onto the femoral head. To the specimens in the experimental group, attenuated impact forces were loaded through the damping material, but those in the control group were subjected to forces directly transmitted without the material. All the impact testing was performed in a temperature and humidity controlled chamber. All of the femoral specimens exposed to the direct impact forces (controlled group) sustained fracture at the neck. The fracture line passed from the base of the femoral head laterally and to the calcar area just proximal to the minor trochanter medially. The location of each fracture line was almost identical among the specimens. None of the specimens that were exposed to the impact force through the damping material (experimental group) sustained fracture macroscopically and roentgenographically.

Augmentation of femoral neck fracture fixation with an injectable calcium-phosphate bone mineral cement.

The first goal of this study was to determine if augmentation with an injectable, in situ setting, calcium-phosphate cement that is capable of being remodeled and was designed to mimic bone mineral significantly improved the strength and stiffness of fixation in a cadaveric femoral neck fracture model. The second goal was to determine if greater increases in fixation strength were achieved as the bone density of the specimen decreased. Sixteen pairs of fresh cadaveric human femora with a mean age of 70.9 years (SD = 17.2 years) were utilized. The bone density of the femoral neck was measured with dual-energy x-ray absorptiometry. The femoral head was impacted vertically with the femoral shaft fixed in 12 degrees of adduction using a materials testing machine to create a fully displaced fracture. Following fracture, 30% inferior comminution was created in each specimen. One randomly chosen femur from each pair underwent anatomic reduction and fixation with three cannulated cancellous bone screws, 7 mm in diameter, in an inverted triangle configuration. The contralateral femur underwent the same fixation augmented with calcium-phosphate cement. Specimens were preconditioned followed by 1.000 cycles to one body weight (611.6 N) at 0.5 Hz to simulate single-limb stance loading. The stiffness in the first cycle was observed to be significantly greater in cement-augmented specimens compared with unaugmented controls (p < 0.05). After cycling, each specimen was loaded at 10 mm/min until complete displacement of the fracture surface and failure of fixation occurred. Specimens augmented with bone mineral cement failed at a mean of 4,573 N (SD = 1,243 N); this was significantly greater (p < 0.01) than the mean for controls (3,092 N, SD = 1,258 N). The relative improvement in fixation strength (augmented/control x 100%) was not inversely correlated to femoral neck bone density (p = 0.25, R2 = 0.09), was weakly correlated to the volume of cement injected (p = 0.07, R2 = 0.22), and was inversely related to the fixation failure load of the control specimen (p = 0.001, R2 = 0.54). There was a mean relative improvement in fixation strength of 169.6% (SD = 77.5). These findings suggest that calcium-phosphate cement provides initial beneficial augmentation to fixation of femoral neck fractures.

Posttraumatic osteonecrosis in a swine model. Correlation of blood cell flux, MRI and histology.

We used a miniature swine femoral neck fracture model to demonstrate the effects of the fracture on blood flow, histologic appearance, MRI signal and the development of posttraumatic osteonecrosis. The fracture was created and internally fixed in the right hip of 11 swine, with the left hip serving as the control. Femoral head blood flow via Laser Doppler Flowmetry and MRI data was examined for the experimental hip preoperatively, postoperatively and at 1, 2, 4 and 8 weeks postfracture. At 8 weeks, the animals were killed and the femoral heads were evaluated. Femoral head blood flow decreased immediately postfracture and continued to diminish with time. MRI signal intensities in the femoral head at 4 and 8 weeks were significantly less when the fixation failed than when it was intact. Histologic grades (0-14 points) and bone densities were 7.6 and 49%, respectively, on the experimental side, compared to 1.6 and 56% on the control side. Histologic grading, bone density values and blood flow data had no relation to changes in MRI signal intensity.