Stiffness Of External Fixation Research Articles

The Interaction of BMP2-Induced Defect Healing in Rat and Fixator Stiffness Modulates Matrix Alignment and Contraction.

ABSTRACTSuccessful fracture healing requires a tight interplay between mechanical and biological cues. In vitro studies illustrated that mechanical loading modulates bone morphogenetic protein (BMP) signaling. However, in the early phases of large bone defect regeneration in vivo, the underlying mechanisms leading to this mechanosensation remained unknown. We investigated the interaction of BMP2 stimulation and mechanical boundary conditions in a rat critical‐sized femoral defect model (5 mm) stabilized with three distinctly different external fixator stiffness. Defects were treated with 5 μg rhBMP2 loaded on an absorbable collagen sponge. Early matrix alignment was monitored by second‐harmonic generation imaging. Bony bridging of defects and successive healing was monitored by histology at day 7 and day 14 as well as in vivo microCT at days 10, 21, and 42 post‐operation. Femora harvested at day 42 were characterized mechanically assessing torsional load to failure ex vivo. At tissue level, differences between groups were visible at day 14 with manifest bone formation in the microCT. Histologically, we observed prolonged chondrogenesis upon flexible fixation, whereas osteogenesis started earlier after rigid and semirigid fixation. At later time points, there was a boost of bone tissue formation upon flexible fixation, whereas other groups already displayed signs of tissue maturation. Based on gene expression profiling, we analyzed the mechanobiological interplay. Already at day 3, these analyses revealed differences in expression pattern, specifically of genes involved in extracellular matrix formation. Gene regulation correlating with fixator stiffness was pronounced at day 7 comprising genes related to immunological processes and cellular contraction. The influence of loading on matrix contraction was further investigated and confirmed in a 3D bioreactor. Taken together, we demonstrate an early onset of mechanical conditions influencing BMP2‐induced defect healing and shed light on gene regulatory networks associated with extracellular matrix organization and contraction that seemed to directly impact healing outcomes. © 2018 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Simulasi Pengaruh Jumlah Lubang pada Ring Fiksasi Eksternal untuk Tulang Tibia

External fixation is a device that is placed out of soft tissue. External fixation device is used to heal open fracture. Open fracture is fracture that soft tissue is broken. That device consist of pin, rod, and clamp. We should pay attention of external fixation stiffness. Number of rod can be increased to get this device more stabil. That device should be stabil so fracture position and pin track doesn’t move. External fixation that consist three rod usually use rin. This research aims to get the effect of external fixation ring holes number to stiffness.

Interaction of age and mechanical stability on bone defect healing: an early transcriptional analysis of fracture hematoma in rat.

Among other stressors, age and mechanical constraints significantly influence regeneration cascades in bone healing. Here, our aim was to identify genes and, through their functional annotation, related biological processes that are influenced by an interaction between the effects of mechanical fixation stability and age. Therefore, at day three post-osteotomy, chip-based whole-genome gene expression analyses of fracture hematoma tissue were performed for four groups of Sprague-Dawley rats with a 1.5-mm osteotomy gap in the femora with varying age (12 vs. 52 weeks - biologically challenging) and external fixator stiffness (mechanically challenging). From 31099 analysed genes, 1103 genes were differentially expressed between the six possible combinations of the four groups and from those 144 genes were identified as statistically significantly influenced by the interaction between age and fixation stability. Functional annotation of these differentially expressed genes revealed an association with extracellular space, cell migration or vasculature development. The chip-based whole-genome gene expression data was validated by q-RT-PCR at days three and seven post-osteotomy for MMP-9 and MMP-13, members of the mechanosensitive matrix metalloproteinase family and key players in cell migration and angiogenesis. Furthermore, we observed an interaction of age and mechanical stimuli in vitro on cell migration of mesenchymal stromal cells. These cells are a subpopulation of the fracture hematoma and are known to be key players in bone regeneration. In summary, these data correspond to and might explain our previously described biomechanical healing outcome after six weeks in response to fixation stiffness variation. In conclusion, our data highlight the importance of analysing the influence of risk factors of fracture healing (e.g. advanced age, suboptimal fixator stability) in combination rather than alone.

Analysis of strategies to increase external fixator stiffness: Is double stacking worth the cost?

We compared the mechanical benefits and costs of 3 strategies that are commonly used to increase knee-spanning external fixator stiffness (resistance to deformation): double stacking, cross-linking, and use of an oblique pin. At our academic trauma centre and biomechanical testing laboratory, we used ultra-high-molecular-weight polyethylene bone models and commercially available external fixator components to simulate knee-spanning external fixation. The models were tested in anterior–posterior bending, medial–lateral bending, axial compression, and torsion. We recorded the construct stiffness for each strategy in all loading modes and assessed a secondary outcome of cost per 10% increase in stiffness. Double stacking significantly increased construct stiffness under anterior–posterior bending (109%), medial–lateral bending (22%), axial compression (150%), and torsion (41%) (p<0.05). Use of an oblique pin significantly increased stiffness under torsion (25%) (p<0.006). Cross-linking significantly increased stiffness only under torsion (29%) (p<0.002). Double stacking increased costs by 84%, cross-linking by 28%, and use of an oblique pin by 15% relative to a standard fixator. All 3 strategies increased stiffness under torsion to varying degrees, but only double stacking increased stiffness in all 4 testing modalities (p<0.05). Double stacking is most effective in increasing resistance to bending, particularly under anterior–posterior bending and axial compression, but requires a relatively high cost increase. Clinicians can use these data to help guide the most cost-effective strategy to increase construct stiffness based on the plane in which stiffness is needed.

Mechanical characterization of external fixator stiffness for a rat femoral fracture model

Clinical and experimental studies have shown that several mechanical factors influence the fracture healing process. One such factor, interfragmentary movement, is affected by loading and the stiffness of the fixation device. This study evaluated the stiffness of different external fixation devices for a rat femoral fracture model, using in vitro and analytical methods. The contribution to the stiffness of the fixation construct was dominated by the flexibility of the pins in relation to their offset, diameter, and material properties. The axial stiffness increased with decreasing offset and increasing pin diameter. Titanium pins resulted in significantly lower axial stiffness compared to stainless steel pins of the same design. The fixator body material and fixator length had a less pronounced influence on fixation stiffness. Mechanically characterized external fixation devices will allow in vivo study of the fracture healing process utilizing pre-calculated fracture fixation stiffness. These characterized fixation devices will allow controlled manipulation of the axial and shear interfragmentary movement to achieve a flexible fixation resulting in callus formation compared to a more rigid fixation limiting callus formation in a rat femoral fracture model.

Biomechanics of Olive Wire Positioning and Tensioning Characteristics

The effect of the olive wire on the stiffness of external fixation was studied previously, but there is limited data on the effect of the olive wire positioning and tensioning characteristics on the stiffness of external fixation. This study evaluated the influence of olive wire positioning (medially, laterally, posteriorly, and anteriorly) and tensioning characteristics (tensioning one end or both ends) on the stiffness of ring external fixation. A fiberglass composite tibia fixed into an idealized ring external frame was tested. All mechanical testing was performed with a servo-hydraulic test frame (MTS Bionix 858, Minneapolis, MN, USA). Load–deformation behavior was compared among different wire design, olive wire positioning and tensioning characteristics under central axial compression, medial compression-bending, posterior compression-bending, posteromedial compression-bending and torsion. The differences between tension values on opposite ends of the wire during different modalities of olive wire tensioning were also investigated. Olive wires tensioned on both ends provided significantly greater bending stiffness compared to smooth wires and olive wires tensioned only on the end opposite to the olive (p < 0.05). There was a significant difference between the tension values on opposite ends of the olive wire during tensioning (p < 0.05). Tensioning both ends of the olive wires and positioning the olives on the side of bending significantly increases the bending stiffness of ring external fixation. This work provides a rationale for clinical decision-making about the use of tensioned olive wires as opposed to smooth wires in ring external fixation.

Transfixion Wire Positioning Within the Bone

The greatest angle that can be formed by the crossing wires at the proximal tibia level without altering safe corridors approaches only 60 degrees. Consequently, the wires are positioned more in the coronal than the sagittal plane. Looking for an increase in sagittal bending stiffness, we evaluated different wire positioning within the proximal tibia and their effect on the stiffness of external fixation of proximal tibia. A fiberglass composite tibia fixed into an idealized ring external frame was tested with a servohydraulic test frame. Load-deformation behavior was compared among the different wire positioning within the proximal tibia under identical conditions of central axial compression, medial compression-bending, posterior compression-bending, posteromedial compression-bending, and torsion. Stiffness values were calculated from the load-deformation and the torque-angle curves. The sample with 3 wires positioned within the bone-2 wires crossed 1 cm posteriorly from the center of the tibia and the third wire placed in coronal plane 1 cm anteriorly from the center of the tibia-was significantly (P < 0.05) stiffer in posterior, posteromedial, and torsional loading configurations compared with all other wire positions within the bone. This new wire positioning within the proximal tibia-2 wires crossed 1 cm posteriorly from the center of the tibia and the third wire placed in coronal plane 1 cm anteriorly from the center of the tibia-increased overall stiffness of external fixation, predominantly in sagittal plane. This work provides a rationale to control proximal tibia external fixation stiffness in sagittal plane.

Biomechanics of Olive Wire Positioning and Tensioning Characteristics

The effect of the olive wire on the stiffness of external fixation has been studied previously, but there are limited data on the effect of the olive wire positioning and tensioning characteristics on the stiffness of external fixation. This study evaluated the influence of olive wire positioning (medially, laterally, posteriorly, and anteriorly) and tensioning characteristics (tensioning one end or both ends) on the stiffness of ring external fixation. A fiberglass composite tibia fixed into an idealized ring external frame was tested. All mechanical testing was performed with a servohydraulic test frame (MTS Bionix 858, Minneapolis, MN). Load-deformation behavior was compared among different wire design and olive wire positioning and tensioning characteristics under central axial compression, medial compression-bending, posterior compression-bending, posteromedial compression-bending, and torsion. The differences between tension values on opposite ends of the wire during different modalities of olive wire tensioning were also investigated. Olive wires tensioned on both ends provided significantly greater bending stiffness compared with smooth wires and olive wires tensioned only on the end opposite to the olive (P < 0.05). There was a significant difference between the tension values on opposite ends of the olive wire during tensioning (P < 0.05). Tensioning both ends of the olive wires and positioning the olives on the side of bending significantly increase the bending stiffness of ring external fixation. This work provides a rationale for clinical decision-making about the use of tensioned olive wires opposed to smooth wires in ring external fixation.

Determination of ankle external fixation stiffness by expedited interactive finite element analysis

Interactive finite element analysis holds the potential to quickly and accurately determine the mechanical stiffness of alternative external fixator frame configurations. Using as an example Ilizarov distraction of the ankle, a finite element model and graphical user interface were developed that provided rapid, construct-specific information on fixation rigidity. After input of specific construct variables, the finite element software determined the resulting tibial displacement for a given configuration in typically 15s. The formulation was employed to investigate constructs used to treat end-stage arthritis, both in a parametric series and for five specific clinical distraction cases. Parametric testing of 15 individual variables revealed that tibial half-pins were much more effective than transfixion wires in limiting axial tibial displacement. Factors most strongly contributing to stiffening the construct included placing the tibia closer to the fixator rings, and mounting the pins to the rings at the nearest circumferential location to the bone. Benchtop mechanical validation results differed inappreciably from the finite element computations.

Stiffness measurement of the neocallus with the Fraktometer FM 100®

The assessment of fracture healing is subjective, and neither radiology nor manual examination allows a reliable determination of bone healing. Fracture healing control in the treatment of tibia shaft fracture with external fixator by a stiffness measurement system (Fraktometer FM 100) is known from clinical studies. The purpose of this study was to follow stiffness control at external fixator in healing of callotasis with the stiffness measurement system. From 1994 to 1997 stiffness measurements with the described system (Fraktometer FM 100) were performed in the BG-Clinic Ludwigshafen to assess the healing course in 11 cases of callotasis at lower limb. In ten cases, regular healing could be followed by signal decrease; in one case, a persistent signal without tendency to decrease was able to reveal callotasis failure at an early point of time. The investigation could also show the importance of bending stiffness control. One case of late axis deformation after fixator removal occurred because of disregarding delayed bending signal decrease. Measurements of the external fixator's stiffness after callotasis can provide useful additional information for further treatment strategy.

The effect of transfixion wire crossing angle on the stiffness of fine wire external fixation: A biomechanical study

To analyse the effect of transfixion wire-crossing angle on the stiffness of fine wire external fixation, a laboratory investigation using a fibreglass tibia fixed into an idealised fixator was performed with a servohydraulic test frame. Load-deformation behaviour was compared at the different wire-crossing angles (30 degrees -90 degrees ) under identical conditions of central axial compression, medial compression-bending, posterior compression-bending, posteromedial compression-bending, and torsion. Stiffness values were calculated from the load-deformation and torque-angle curves. The increase in wire-crossing angle led to an overall increase in the stiffness, except medial bending stiffness. The wire-crossing angle of 90 degrees provided significantly greater stiffness than all other angles in all load configurations (p<0.05) except medial bending. In medial bending, the wire-crossing angle of 30 degrees provided significantly greater stiffness than all the other angles (p<0.05). Increasing wire-crossing angle from 30 degrees to 90 degrees contributed to an overall increase of 75% in external fixation stiffness, which included axial, torsional, and bending stiffness, but bending stiffness was a function of the wire positioning with respect to the loading axis. Therefore, using the widest possible wire-crossing angle and placing wires as close to the loading plane as possible can increase the stiffness of external fixation.

Determination of ankle external fixation stiffness by expedited interactive finite element analysis

Interactive finite element analysis holds the potential to quickly and accurately determine the mechanical stiffness of alternative external fixator frame configurations. Using as an example Ilizarov distraction of the ankle, a finite element model and graphical user interface were developed that provided rapid, construct-specific information on fixation rigidity. After input of specific construct variables, the finite element software determined the resulting tibial displacement for a given configuration in typically 15 s. The formulation was employed to investigate constructs used to treat end-stage arthritis, both in a parametric series and for five specific clinical distraction cases. Parametric testing of 15 individual variables revealed that tibial half-pins were much more effective than transfixion wires in limiting axial tibial displacement. Factors most strongly contributing to stiffening the construct included placing the tibia closer to the fixator rings, and mounting the pins to the rings at the nearest circumferential location to the bone. Benchtop mechanical validation results differed inappreciably from the finite element computations.

Effect of Clamp Type on Type II External Fixator Stiffness

SummaryIn order to investigate the effects of two clamp types on type II external fixator stiffness, models using wooden dowels were constructed and mechanically tested. Kirschner-Ehmer clamps were compared to Securos clamps in four-pin type II external fixator configurations. Increasing axial loads were applied and displacement at a gap in the centre of the model measured. Linear regression and comparison of the slope of the regression lines before yield, after yield, and throughout 700N assessed model performance. The resulting load displacement curves were linear. There was no difference in model stiffness before yield, but was greater with models constructed with Securos clamps after yield and overall. The mean relative stiffness of the models constructed with the Kirschner-Ehmer type clamps were 320 ± 53.8 Newtons/mm, and with models constructed with Securos type clamps were 425 ± 74.8 Newtons/mm. Utilizing Securos clamps resulted in significantly (p&lt;0.05) greater frame stiffness that is attributable to higher load at yield and greater stiffness after yield. Increasing resistance to rotational moments at the clamp/connecting bar junction should result in less stress imparted to the bone/pin interface, decreasing strain and decreasing pin loosening.Axial stiffness in models of bilateral external fixators using Kirschner-Ehmer type clamps versus Securos clamps were compared. The stiffness of fixators constructed with Securos clamps was greater overall and at high loads due to a more secure fixation pin/connecting bar junction. Increased fixator stiffness would result in less stress at the bone/pin interface and may contribute to less pin loosening.

THE EFFECT OF EXTERNAL FIXATION STIFFNESS ON EARLY HEALING OF TRANSVERSE OSTEOTOMIES

Veterinary SurgeryVolume 19, Issue 3 p. 236-236 THE EFFECT OF EXTERNAL FIXATION STIFFNESS ON EARLY HEALING OF TRANSVERSE OSTEOTOMIES First published: May 1990 https://doi.org/10.1111/j.1532-950X.1990.tb01177.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue3May 1990Pages 236-236 RelatedInformation

The effect of external fixation stiffness on early healing of transverse osteotomies.

The effect of bending stiffness of external fixators on the early healing of transverse tibial osteotomies was studied in a canine model to determine whether there is a particular range of fixation stiffness where healing is poor. Five unilateral fixators with different stiffnesses were developed and employed along with a dynamic compression plate to fix experimental osteotomies of dog tibias and the contralateral intact tibias served as controls. The six experimental fixation devices were: plate (P), stainless steel sidebar fixator (SS), stiff aluminum sidebar fixator (SA), intermediate aluminum sidebar fixator (IA), flexible aluminum sidebar fixator (FA), and Delrin sidebar fixator (D). Compared with human tibial fixation methods, the fixators ranged from a rigidity greater than a plate on a human tibia to a flexibility similar to a plaster cast on a human lower leg. Sixty-four adult male mongrel dogs (29 +/- 3 kg) underwent surgery and 52 completed the 9-week study, leaving 7 to 10 dogs in each experimental group (P = 8, SS = 7, SA = 9, IA = 9, FA = 10, D = 9). After the 9-week survival period the experimental tibias were radiographed and callus area was digitized. Both the experimental and control tibias were then tested to failure in four-point bending, and failure moment, stiffness, and energy to failure were determined. Of the 52 osteotomies, only four developed nonunions: 3 of 10 in the FA group and 1 of 7 in the SS group. Using analysis of variance, no statistical differences were detected in failure force, stiffness, or energy to failure as a function of fixator groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of fixation stiffness on fracture healing. External fixation of tibial osteotomy in the rabbit.

In rabbit tibial osteotomies, the effects on bone healing of three different degrees of stiffness of external fixation were investigated. Redislocation occurred in one third of the osteotomies with the least rigid fixation, and the amount of external callus was greater in this group. At 6 weeks there were no significant differences between the groups regarding bending strength and stiffness of the bones.