Axial Interfragmentary Movement Research Articles

Material Properties and Engineering Performance of Bone Fracture Plates Made from Plant Fiber Reinforced Composites: A Review.

Bone fracture plates are usually made from titanium alloy or stainless steel, which are much stiffer than bone. However, overly stiff plates can restrict axial interfragmentary motion at the fracture leading to delayed callus formation and healing, as well as causing bone "stress shielding" under the plate leading to bone atrophy, bone resorption, and plate loosening. Consequently, there have been many prior efforts to develop nonmetallic bone fracture plates with customized material properties using synthetic fibers (e.g., aramid, carbon, glass) in polymer resin. Even so, plant fibers (e.g., flax, roselle, sisal) offer additional advantages over synthetic fibers, such as availability, biodegradability, less toxicity during processing, lower financial cost, and recyclability. As such, there is an emerging interest in using plant fibers alone, or combined with synthetic fibers, to reinforce polymers for various applications. Thus, this is the first review article on the material properties and engineering performance of innovative bone fracture plates made from composite materials reinforced by plant fibers alone or supplemented using synthetic fibers. This article presents material-level fiber properties (e.g., elastic modulus, ultimate strength), material-level plate properties (e.g., fatigue strength, impact toughness), and bone-plate engineering performance (e.g., overall stiffness, plate stress), as well as discussing general findings, study quality, and future work. This article may help engineers and surgeons to design, fabricate, analyze, and utilize novel bone fracture plates.

Biomechanical testing of a computationally optimized far cortical locking plate versus traditional implants for distal femur fracture repair

BackgroundThis study experimentally validated a computationally optimized screw number and screw distribution far cortical locking distal femur fracture plate and compared the results to traditional implants. Methods24 artificial femurs were osteotomized with a 10 mm fracture gap 60 mm proximal to the intercondylar notch. Three fixation constructs were used. (i) Standard locking plates secured with three far cortical locking screws inserted according to a previously optimized distribution in the femur shaft (n = 8). (ii) Standard locking plates secured with four standard locking screws inserted in alternating plate holes in the femur shaft (n = 8). (iii) Retrograde intramedullary nail secured proximally with one anterior-posterior screw and distally with two oblique screws (n = 8). Axial hip forces (700 and 2800 N) were applied while measuring axial interfragmentary motion, shear interfragmentary motion, and overall stiffness. FindingsExperimental far cortical locking plate results compared well to published computational findings. Far cortical locking femurs contained the highest axial motion within the potential ideal range of 0.2–1 mm and a sheer-to-axial motion ratio < 1.6 at toe-touch weight-bearing (700 N). At full weight-bearing (2800 N), Standard locking-plated femurs had the only axial motion within 0.2–1 mm but had an excess shear-to-axial motion ratio. Nail-implanted femurs underperformed at both forces. InterpretationFor toe-touch weight-bearing, the far cortical locking construct provided optimal biomechanics to allow moderate motion, which has been suggested to encourage early callus formation. Conversely, at full weight-bearing, the standard locking construct offered the biomechanical advantage on fracture motion.

Spatial Bridge Locking Fixator versus Traditional Locking Plates in Treating AO/OTA 32-A3.2 Fracture: Finite Element Analysis and Biomechanical Evaluation.

ObjectiveTo compare the biomechanical behaviors of the spatial bridge locking fixator (SBLF), single locking plate (SP), and double locking plate (DP) for AO/OTA 32‐A3.2 fractures using finite element analysis and biomechanical tests.MethodsAxial loading of 700 N was conducted on the AO/OTA 32‐A3.2 model via finite element analysis. The von Mises stress and the interfragmentary movement (IFM) were comparatively analyzed in the three configurations above. On the mechanical tester, axial and torsional loading of 30 synthetic femurs (five specimens of each configuration for each test at random) was performed, and the interfragmentary movement, torsion angle, stiffness, and ultimate load were recorded and analyzed.ResultsThe finite element analysis (FEA) results showed that the von Mises stress of the spatial bridge locking fixator (SBLF) was lower than that of the single locking plate (SP) and higher than that of the double locking plate (DP). At 700 N, the axial IFMs were 0.15–0.38 mm (SBLF), 0.03–0.84 mm (SP), and 0.02–0.07 mm (DP). The biomechanical experiment indicated that the axial interfragmentary movements (IFMs) were 0.44 ± 0.23 mm (SBLF), 1.02 ± 0.40 mm (SP), and 0.07 ± 0.07 mm (DP) (p < 0.001). The axial IFM of the SBLF group had the highest probability (79.26%) of falling within the ideal range (0.2–0.8 mm), and the SP and DP groups had probabilities of 27.10% and 3.14%, respectively. The axial stiffness in the SBLF group (1586 ± 130 N/mm) was significantly lower than that in the DP group (10,264 ± 2671 N/mm) (p < 0.001) but greater than that in the SP group (725 ± 178 N/mm) (p = 0.396). The range of axial loads to ultimate failure was 3385–4527 N (SBLF), 3377–4664 N (SP), and 3780–4804 N (DP). The shear motion of the fracture end was 0.35 ± 0.14 mm (SBLF), 0.16 ± 0.10 mm (SP), and 0.08 ± 0.04 mm (DP) (p < 0.001). The torsional stiffness was 1.68 ± 0.14 Nm/degree (SBLF), 2.32 ± 0.29 Nm/degree (SP) (SBLF&SP, p < 0.001), and 3.53 ± 0.73 Nm/degree (DP) (SBLF&DP, p < 0.001).ConclusionsThe SBLF structure may exhibit a better biomechanical performance compared with the SP and DP in providing the best quantity and more symmetrical interfragmentary movement for AO/OTA 32‐A3.2 fractures.

Biomechanical design of a new percutaneous locked plate for comminuted proximal tibia fractures

Comminuted proximal tibia fractures are an ongoing surgical challenge. This “proof of concept” study is the first step in designing a new percutaneous plate for this injury under toe-touch weight-bearing as prescribed after surgery. Finite element simulations generated design curves for overall stiffness, bone and implant stress, and interfragmentary motion using 3 fixations (no, 1, or 2 “kickstand” (KS) screws across the fracture gap) over a range of plate elastic moduli (EP = 5 to 200 GPa). Combining well-established optimization criteria to enhance callus formation (i.e. 0.2 mm ≤ axial interfragmentary motion ≤ 1 mm; shear / axial interfragmentary motion ratio < 1.6), lessen stress shielding (i.e. bone stress under the proposed plate > bone stress under a traditional titanium or steel plate), and reduce steel screw breakage (i.e. screw max stress < ultimate tensile stress of steel) resulted in plate design recommendations: 172.6 ≤ EP < 200 GPa (no KS screw), 79.8 ≤ EP < 100 GPa (1 KS screw), and 4.9 ≤ EP < 100 GPa (2 KS screws). A prototype plate could be made from materials currently used or proposed for orthopaedics, such as polymers, fiber-reinforced polymers, fiber metal laminates, metal foams, or shape memory alloys.

A novel intramedullary nail to control interfragmentary motion in diaphyseal tibial fractures.

Numerous animal and human studies have demonstrated the benefit of controlled interfragmentary motion on fracture healing. In this study, we quantified interfragmentary motion and load transfer in tibial fractures fixed using a novel intramedullary nail (IMN) that allows controlled axial motion. Fifty composite tibias with various fracture patterns were utilized. For all test conditions, two interlocking screws were used to fix the nail in the proximal metaphysis, and two interlocking screws through the distal metaphysis. The nail allowed either no motion (static mode) or 1 mm (dynamic mode) of cyclic axial motion between the two fracture fragments for every fracture pattern tested. As expected, strain shielding was more prominent under static nail conditions. In contrast, specimens tested under dynamic nail conditions transferred axial load between the fracture fragments such that strains near the fracture site were generally similar to those measured on an intact tibia. Maximum shear strains proximal to the fracture were significantly lower in specimens with oblique or butterfly fracture patterns (p < 0.01) compared to intact specimens. This decrease in shear strain indicates that strain shielding effects were likely present due to the implant. However, strain shielding appeared to be reduced in tensile and compressive principal strains. In summary, the novel IMN allowed controlled axial motion between the fragments in a variety of common diaphyseal tibial fracture patterns.Clinical Significance: The present in vitro biomechanical study investigated a novel intramedullary nail capable of controlled axial interfragmentary motion which may potentially enhance fracture healing.

Biomechanical optimization of the far cortical locking technique for early healing of distal femur fractures

This finite element study optimized far cortical locking (FCL) technology for early callus formation in distal femur fracture fixation with a 9-hole plate using FCL screws proximal to, and standard locking screws distal to, the fracture. Analyses were done for 120 possible FCL screw configurations by varying FCL screw distribution and number. A hip joint force of 700 N (i.e. 100% x body weight) was used, which corresponds to a typical 140 N “toe-touch” foot-to-ground force (i.e. 20% x body weight) suggested to patients immediately after surgery. Increased FCL screw distribution (i.e. shorter plate working length) caused a decrease at the medial side and an increase at the lateral side of the axial interfragmentary motion (AIM), mildly affected shaft and condylar cortex Von Mises max stress (σMAX), increased plate σMAX, and decreased shaft FCL screw and condylar locking screw σMAX. Increased FCL screw number decreased AIM and σMAX on the shaft cortex, condylar cortex, plate, and FCL screws, but not condylar screws. The optimal FCL screw configuration had 3 FCL screws in plate holes #1, 5, and 6 (proximal to distal) for optimal AIM of 0.2 - 1 mm and reduce shear fracture motion, thereby encouraging early callus formation.

Biomechanical design using in-vitro finite element modeling of distal femur fracture plates made from semi-rigid materials versus traditional metals for post-operative toe-touch weight-bearing

This proof-of-concept study designs distal femur fracture plates from semi-rigid materials vs. traditional metals for toe-touch weight-bearing recommended to patients immediately after surgery. The two-fold goal was to (a) reduce stress shielding (SS) by increasing cortical bone stress thereby reducing the risk of bone absorption and plate loosening, and (b) reduce delayed healing (DH) via early callus formation by optimizing axial interfragmentary motion (AIM). Finite element analysis was used to design semi-rigid plates whose elastic moduli E ensured plates permitted AIM of 0.2 - 1 mm for early callus formation. A low hip joint force of 700 N (i.e. 100% x body weight) was applied, which corresponds to a typical 140 N toe-touch foot-to-ground force (i.e. 20% x body weight) recommended to patients after surgery. Analysis was done using 2 screw materials (steel or titanium) and types (locked or non-locked). Steel and titanium plates were also analyzed. Semi-rigid plates (vs. metal plates) had lower overall femur/plate construct stiffnesses of 508 - 1482 N/mm, higher cortical bone stresses under the plate by 2.02x - 3.27x thereby reducing SS, and lower E values of 414 - 2302 MPa to permit AIM of 0.2 - 1 mm thereby reducing DH.

Intramembranous bone formation after callus distraction is augmented by increasing axial compressive strain.

The mechanical environment is a primary factor in the success of distraction osteogenesis. It is known that the interfragmentary movement during the distraction and maturation phase effects the callus formation. In addition to cyclic compression, other movements like shear and bending influence the bone formation process as shown in previous callus distraction studies. Reports of cartilage presence and endochondral ossification in the regenerative zone have been associated with a lack of fixation stability and delayed healing. So far the effects of the direction of interfragmentary movements could not be studied separately. By means of a unique lateral callus distraction model, we investigated the effects of small (0.1 mm) and moderate (0.6 mm), purely axial compression on ossification during callus maturation in sheep. A distraction device incorporating a mobile titanium plate was mounted on the tibia. Following lateral callus distraction, electromechanically controlled movements allowed purely axial cyclic compression of the tissue regenerate. Seven weeks post-operatively, the tissue regenerates were investigated using μCT, histology and immunohistochemistry. The larger amplitude significantly increased bone formation (Fractional bone volume: 19.4% vs. 5.2%, p = 0.03; trabecular thickness: 0.1 mm vs. 0.06 mm, p = 0.006; mean spicule height: 2.6 mm vs. 1.1 mm, p = 0.02) however, no endochondral ossification occurred. The elimination of shear movement, unimpaired neovascularization as well as the tensile strain stimuli during the distraction phase suppressing chondrogenic differentiation may all contribute to the absence of cartilage. In clinical application of distraction osteogenesis, moderate axial interfragmentary movement augments intramembranous ossification provided shear strain is minimized.

Influence of fracture geometry on bone healing under locking plate fixations: A comparison between oblique and transverse tibial fractures

Mechano-regulation plays a crucial role in bone healing and involves complex cellular events. In this study, we investigate the change of mechanical microenvironment of stem cells within early fracture callus as a result of the change of fracture obliquity, gap size and fixation configuration using mechanical testing in conjunction with computational modelling. The research outcomes show that angle of obliquity (θ) has significant effects on interfragmentary movement (IFM) which influences mechanical microenvironment of the callus cells. Axial IFM at near cortex of fracture decreases with θ, while shear IFM significantly increases with θ. While a large θ can increase shear IFM by four-fold compared to transverse fracture, it also result in the tension–stress effect at near cortex of fracture callus. In addition, mechanical stimuli for cell differentiation within the callus are found to be strongly negatively correlated to angle of obliquity and gap size. It is also shown that a relatively flexible fixation could enhance callus formation in presence of a large gap but could lead to excessive callus strain and interstitial fluid flow when a small transverse fracture gap is present. In conclusion, there appears to be an optimal fixation configuration for a given angle of obliquity and gap size.

Biomechanical evaluation of intramedullary nail and bone plate for the fixation of distal metaphyseal fractures

Surgical treatment of distal metaphyseal fractures remains problematic, and whilst both intramedullary nailing and bone plate fixation are known as the acceptable methods for the internal fixation of this kind of fractures, neither technique demonstrated satisfactory clinical outcomes. In this research, a finite element based investigation was made to compare these two fixation techniques for the fixation of distal tibia fractures from the biomechanics point of view. For this purpose, a 3mm transverse fracture gap was created at the distal metaphyseal region of tibia and fixed by use of either a nail or a plate. The von Mises stress, interfragmentary movements, and the production of different tissue phenotypes at the fracture site were calculated. Results of this study showed that plating offers more advantageous biomechanical conditions at the fracture site, in which it provides sufficient amount of axial interfragmentary movement and considerable amount of cartilage production, while intramedullary nailing restricts axial movements but causes high magnitude of shear movements. However, nailing is superior to plating from the mechanical point of view and provides earlier weight bearing. In addition, it was shown that by using composite materials, biomechanical behavior of both fixation techniques will be improved through decreasing risk of failure and promoting cartilaginous tissue production.

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

BackgroundExtent 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. MethodsSimple 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. ResultsDifferent 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 ≥62mm (p ≤ 0.003). ConclusionMechanical 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 42–62mm. Fixation with sLS demonstrated significantly more axial IFM underneath the plate and may further contribute to compensation of asymmetric straining.

The Flexible Axial Stimulation (FAST) intramedullary nail provides interfragmentary micromotion and enhanced torsional stability

BackgroundRecent advances in intramedullary (IM) nailing have focused on removing free play at the nail-screw interface to provide enhanced construct torsional stiffness. These changes also increase axial construct stiffness and reduce axial interfragmentary movement, which is required for optimal secondary fracture healing. This study tested whether a novel intramedullary nail, the Flexible Axial Stimulation (FAST) nail, can simultaneously provide controlled axial interfragmentary motion with enhanced torsional stiffness. MethodsNovel tibial nails and matched controls (N=6 per group) were tested in a cadaveric osteotomy fracture model and in explanted bench testing. In cadaver and bench tests, nails were tested in axial tension/compression, torsion, bending, and shear. Overall construct stiffness values were calculated in each loading mode and axial and torsional low-load micromotion plateaus were quantified. FindingsThe novel nails produced 1mm of controlled axial interfragmentary motion, which was associated with a 22% reduction in axial stiffness compared to standard controls (P=0.026, effect size 2.5). The novel constructs also allowed less low-load torsional movement compared to the controls (3.8deg vs. 7.1deg, P=0.010, effect size 1.9), which was associated with a 14% increase in overall construct torsional stiffness (P=0.003, effect size 1.3). There were no observable differences in performance between the novel and control nails in anteroposterior/mediolateral bending or shear. InterpretationThese results suggest that an IM nailing construct can provide axial interfragmentary motion while retaining high torsional stiffness, a combination which may potentially enhance healing.

Controlled Dynamization to Enhance Reconstruction Capacity of Tissue-Engineered Bone in Healing Critically Sized Bone Defects: AnIn VivoStudy in Goats

Tissue-engineered bone (TEB) has shown to be an effective alternative to conventional gold-standard autogenous bone for the repair of critically sized bone defects (CSBD). Moderate axial interfragmentary movement (IFM) has been shown to promote bone healing in conventional models. This study explored the use of IFM to enhance the capacity of TEB in the repair of CSBD using a goat model. CSBD were created in a goat model. Dynamic intramedullary rods designed to supply axial IFMs within 10% of the interfragmentary strain were used to stabilize CSBD goat femur models, whose bone defects were filled with TEB. Bone regeneration was evaluated using radionuclide bone imaging, roentgenographic analysis, periosteal callus area, computed tomography value score, biomechanical analysis, and histological observation. Compared with the static intramedullary rods, the dynamic intramedullary rod group showed an increase in early-stage callus formation and blood supply to the callus tissue, better differentiation of fibrous and cartilaginous tissue into bone tissue, improved strength and stiffness of callus tissue in late-stage healing, and overall better functional recovery of the goat femur. This showed that moderate axial IFM could promote the osteogenesis and reconstruction of TEB in vivo.

The fracture gap size influences the local vascularization and tissue differentiation in callus healing.

Revascularization of a fracture depends on fracture stability and fracture gap conditions. The aim of the study was to determine quantitatively the revascularization and tissue differentiation in an animal model with different fracture gaps and controlled biomechanical conditions. The study was performed on ten sheep with an osteotomy on the right metatarsal. The fracture was stabilized by an external fixator that allowed adjustable axial interfragmentary movement. Two groups of five sheep each were adjusted to a medium sized gap (M, 2.1 mm) and a large gap (L, 5.7 mm) under comparable interfragmentary strain (30-32%). The animals were killed after 9 weeks, and the metatarsals were prepared for undecalcified histology and analysis of tissue differentiation and vessel distribution. Group M showed significantly more revascularization (M=1.62, L=0.85 vessels/mm2), more bone formation (M=37.2%, L=13.9%) and less fibrocartilage tissue (M=18.1%, L=39.1%) than group L. Larger vessels (>40 microm) were found mainly in the medullary channel, and smaller vessels (<20 microm) mainly in the peripheral callus. Histologically, group M showed partial bony bridging of the osteotomy gap, and the group L had delayed healing. A good reduction of a fracture with small interfragmentary gaps is important for its revascularization and healing.

Interaction between active motion and exogenous transforming growth factor Beta during tibial fracture repair.

Evaluate the effects of axial motion and transforming growth factor beta (TGF-beta) on callus formation and fracture healing.DESIGN Prospective experimental design with a 39-day postfracture recovery. Unrestricted cage activity with weight bearing as tolerated. Twenty-two skeletally mature, female New Zealand White rabbits. Displaced, closed tibial fractures were reduced and stabilized in external fixators on the fourth day following fracture. Half of the fixators were locked for the duration of healing. The other fixators were locked for one week, then unlocked for the remaining four weeks. Half of the fractures in each fixator group received two injections of recombinant human TGF-beta1 (rhTGF-beta1). One injection was administered at the time of reduction, and the second was given 48 hours later. Interfragmentary axial motion was measured during floor activity. Biomechanical properties were measured during a torsion test to failure. Callus area and the distribution of tissues within the callus were determined by computer-aided histomorphometry. The administration of TGF-beta1 did not alter callus size, mechanical properties, or the distribution of tissues in the callus of fractures that were stabilized in locked external fixators. Recoverable axial motion fixation increased callus size, quantity of mineralized bone bridging the fracture, and maximum torque relative to locked fixation. The injection of TGF-beta1 negated the beneficial effects of axial motion by promoting the formation of a peripheral callus bridged by fibrous tissue rather than mineralized trabecular bone. Injection of rhTGF-beta1 during the first postfracture week does not provide a biologic boost that improves fracture healing. Injection of TGF-beta1 may be detrimental to healing under conditions when fracture motion is present. The results suggest that there is a tendency for exposure to TGF-beta1 to inhibit the normal development of peripheral callus in response to axial interfragmentary motion.

The influence of stiffness of the fixator on maturation of callus after segmental transport

The treatment of large bony defects by callus distraction is well accepted, but the duration of treatment is long and the rate of complications increases accordingly. We have examined the effect of the stiffness of the axial fixator on reducing the time for maturation of callus. We created a mid-diaphyseal defect of 15 mm in the metatarsal bone in sheep and stabilised it with a ring fixator. After four days a bony segment was transported for 16 days at 1 mm per day. After 64 days the animals were divided into four groups, three with axial interfragmentary movement (IFM) of 0.5, 1.2 and 3.0 mm, respectively, and a control group. The 3.0 mm IFM group had the smallest bone density (p = 0.001) and area of callus and the largest IFM after 12 weeks; it also had typical clinical signs of hypertrophic nonunion. The most rapid stiffening of the callus was in the 0.5 mm group which had the smallest IFM (p = 0.04) after 12 weeks and radiological signs of bridging of the defect. These results indicate that suitable dynamic axial stimulation can enhance maturation of distraction callus when the initial amplitude is small, but that a large IFM can lead to delayed union.

The influence of stiffness of the fixator on maturation of callus after segmental transport

The Journal of Bone and Joint Surgery. British volumeVol. 82-B, No. 1 ResearchFree AccessThe influence of stiffness of the fixator on maturation of callus after segmental transportL. Claes, J. Laule, K. Wenger, G. Suger, U. Liener, L. KinzlL. ClaesProfessor and DirectorDepartment of Orthopaedic Research and BiomechanicsSearch for more papers by this author, J. LauleResearch FellowDepartment of Orthopaedic Research and BiomechanicsSearch for more papers by this author, K. WengerResearch FellowDepartment of Orthopaedic Research and BiomechanicsSearch for more papers by this author, G. SugerOrthopaedic SurgeonDepartment of Surgery, University of Ulm, Helmholtzstrasse 14, D-89081 Ulm, Germany.Search for more papers by this author, U. LienerOrthopaedic SurgeonDepartment of Surgery, University of Ulm, Helmholtzstrasse 14, D-89081 Ulm, Germany.Search for more papers by this author, L. KinzlProfessorDepartment of Surgery, University of Ulm, Helmholtzstrasse 14, D-89081 Ulm, Germany.Search for more papers by this authorPublished Online:1 Jan 2000https://doi.org/10.1302/0301-620X.82B1.0820142AboutSectionsPDF/EPUB ToolsAdd to FavouritesDownload CitationsTrack CitationsPermissions ShareShare onFacebookTwitterLinked InRedditEmail AbstractThe treatment of large bony defects by callus distraction is well accepted, but the duration of treatment is long and the rate of complications increases accordingly. We have examined the effect of the stiffness of the axial fixator on reducing the time for maturation of callus.We created a mid-diaphyseal defect of 15 mm in the metatarsal bone in sheep and stabilised it with a ring fixator. After four days a bony segment was transported for 16 days at 1 mm per day. After 64 days the animals were divided into four groups, three with axial interfragmentary movement (IFM) of 0.5, 1.2 and 3.0 mm, respectively, and a control group.The 3.0 mm IFM group had the smallest bone density (p = 0.001) and area of callus and the largest IFM after 12 weeks; it also had typical clinical signs of hypertrophic nonunion. The most rapid stiffening of the callus was in the 0.5 mm group which had the smallest IFM (p = 0.04) after 12 weeks and radiological signs of bridging of the defect. These results indicate that suitable dynamic axial stimulation can enhance maturation of distraction callus when the initial amplitude is small, but that a large IFM can lead to delayed union.FiguresReferencesRelatedDetailsCited byEffect of the accordion technique on bone regeneration during distraction osteogenesis: A computational studyComputer Methods and Programs in Biomedicine, Vol. 227A new design for the humerus fixation plate using a novel reliability-based topology optimization approach to mitigate the stress shielding effectClinical Biomechanics, Vol. 99Biomechanical Performance Analysis of the Monolateral External Fixation Devices with Steel and Composite Material Frames under the Impact of Axial Load12 January 2022 | Applied Sciences, Vol. 12, No. 2Enhancing the Efficiency of Distraction Osteogenesis through Rate-Varying Distraction: A Computational Study29 October 2021 | International Journal of Molecular Sciences, Vol. 22, No. 21Development of Knowledge-Based Engineering System for Structural Size Optimization of External Fixation Device15 November 2021 | Applied Sciences, Vol. 11, No. 22Mechanobiology of Bone Consolidation During Distraction Osteogenesis: Bone Lengthening Vs. Bone Transport27 October 2020 | Annals of Biomedical Engineering, Vol. 49, No. 4Mechanical Influence of Surrounding Soft Tissue on Bone Regeneration Processes: A Bone Lengthening Study17 August 2020 | Annals of Biomedical Engineering, Vol. 49, No. 2Elastic Modulus of Woven Bone: Correlation with Evolution of Porosity and X-ray Greyscale9 May 2020 | Annals of Biomedical Engineering, Vol. 49, No. 1Real-Time Wireless Platform for In Vivo Monitoring of Bone Regeneration15 August 2020 | Sensors, Vol. 20, No. 16Percutaneous CO2 Treatment Accelerates Bone Generation During Distraction Osteogenesis in Rabbits21 May 2020 | Clinical Orthopaedics & Related Research, Vol. 478, No. 8Evolution of callus tissue behavior during stable distraction osteogenesisJournal of the Mechanical Behavior of Biomedical Materials, Vol. 85Mechanical characterization via nanoindentation of the woven bone developed during bone transportJournal of the Mechanical Behavior of Biomedical Materials, Vol. 74Model of the distraction callus tissue behavior during bone transport based in experiments in vivoJournal of the Mechanical Behavior of Biomedical Materials, Vol. 61Treatment of high-energy tibial plateau fractures14 December 2006 | Strategies in Trauma and Limb Reconstruction, Vol. 1, No. 1Low-Intensity Ultrasound Enhances Maturation of Callus after Segmental TransportClinical Orthopaedics & Related Research, Vol. 430Effects of timing of low-intensity pulsed ultrasound on distraction osteogenesis1 January 2006 | Journal of Orthopaedic Research, Vol. 22, No. 2 Vol. 82-B, No. 1 Metrics History Published online 1 January 2000 Published in print 1 January 2000 InformationCopyright © 2000, The British Editorial Society of Bone and Joint Surgery: All rights reservedPDF download

Influence of size and stability of the osteotomy gap on the success of fracture healing.

Flexible fixation of fractures with minimally invasive surgical techniques has become increasingly popular. Such techniques can lead to relatively large fracture gaps (larger than 5 mm) and considerable interfragmentary movements (0.2-5 mm). We investigated the influence of the size of the fracture gap, interfragmentary movement, and interfragmentary strain on the quality of fracture healing. A simple diaphyseal long-bone fracture was modeled by means of a transverse osteotomy of the right metatarsus in sheep. In 42 sheep, the metatarsus was stabilized with a custom-made external ring fixator that was adjustable for gap size and axial interfragmentary movement. The sheep were randomly divided into six groups with three different gap sizes (1, 2, or 6 mm) and small or large interfragmentary strain (approximately 7 or 31%). The movement of the fracture gap was monitored telemetrically by a displacement transducer attached to the fixator. After 9 weeks of healing, the explanted metatarsus was evaluated mechanically in a three-point bending test to determine bending stiffness and was radiographed to measure the amount of periosteal callus formation. Increased size of the gap (from 1 to 6 mm) resulted in a significant reduction in the bending stiffness of the healed bones. Larger interfragmentary movements and strains (31 compared with 7%) stimulated larger callus formation for small gaps (1-2 mm) but not for larger gaps (approximately 6 mm). The treatment of simple diaphyseal fractures with flexible fixation can be improved by careful reduction of the fracture; this prevents large interfragmentary gaps. The experimental fracture model for the metatarsus showed that the healing process was inferior when the gap was larger than 2 mm.

Effect of dynamization on gap healing of diaphyseal fractures under external fixation

We asked whether dynamization of externally fixed diaphyseal fractures could improve bone healing in comparison to rigid fixation of fractures having similar remaining gap sizes. To answer this question we evaluated metatarsal osteotomies in 12 sheep. The osteotomy with a 0.6-mm gap was stabilized with a specially designed high bending and torsional stiffness external ring fixator. Osteotomies in six sheep were stabilized rigidly (axial movement < 0.06 mm) or dynamically (axial movement 0.15–0.34 mm). The cyclical axial interfragmentary movement was caused by the load-bearing of the operated limb. With increasing healing time, the initially allowed movement was decreased by callus formation around the osteotomy. The reduction in interfragmentary movement was measured and monitored by a linear variable displacement transducer at the external fixator and a telemetry system. After 9 weeks the sheep were sacrificed and the healed bones were investigated biomechanically and histomorphologically. Compared to the rigidly fixed osteotomies, the dynamized osteotomies showed significantly ( P < 0.05) greater (+41%) callus formation and 45% greater tensile strength of the newly formed bone in the cortical osteotomy gap. Histological analysis indicated that the effect of dynamization occurred mainly after the 5th week.