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

Mechanical evaluation of revision surgery for femoral shaft nonunion initially treated with intramedullary nailing: Exchange nailing versus augmentation plating

INTRODUCTION

Exchange nailing (EN) or augmentation plating (AP) has been employed to treat nonunions after intramedullary nailing for femoral shaft fractures. Although instability is a factor in hypertrophic nonunion, mechanical evaluations have been limited because the contribution of the callus to fracture site stability varies with healing. Our previous study illustrated the potential for evaluation using a finite element analysis (FEA) that incorporates callus material properties. This study aimed to mechanically evaluate revision surgery for nonunions using FEA.

MATERIALS AND METHODS

A quantitative computed tomography-based FEA was performed on virtual revision models of a patient with suspected nonunion after intramedullary nailing. In addition to the initial nailing model (IN) with an 11-mm diameter (D) and 360-mm length (L), four EN models with D12mm (EN1), D13mm (EN2), D12mm-L400mm (EN3), and D13mm-L400mm (EN4) nails and three AP models with 5- (AP1), 6- (AP2), and 7-hole (AP3) plates were created. As with bone, callus was assigned inhomogeneous material properties derived from density based on an empirical formula. The hip joint reaction force and muscle forces at maximum load during the gait cycle were applied. The volume ratio of the callus at the fracture site with a tensile failure risk of ≥1 (tensile failure ratio) and bone fragment movement were evaluated.

RESULTS

The tensile failure ratio was 11.6 % (IN), 10.1 % (EN1), 6.3 % (EN2), 10.9 % (EN3), 6.2 % (EN4), 6.4 % (AP1), 7.2 % (AP2), and 7.7 % (AP3), respectively. The bone fragment movement showed an opening on the lateral side with the initial intramedullary nailing. However, both revision surgeries reduced the opening, leading to compression except in the EN1 model. The proximal bone fragments were internally rotated relative to the distal fragments, and the rotational instability was more suppressed in models with lower tensile failure ratio.

CONCLUSIONS

For EN, the increase in diameter, not length, is important to suppress instability. AP reduces instability, comparable to a 2 mm increase in nail diameter, and screw fixation closer to the fracture site reduces instability. This study suggest that AP is mechanically equivalent to EN and could be an option for revision surgery for femoral shaft nonunions.

Helical Plating Compared with Straight Plating and Nailing for Treatment of Proximal Third Humeral Shaft Fractures-A Biomechanical Study

Background and Objectives: The surgical treatment of proximal humeral shaft fractures usually considers application of either long straight plates or intramedullary nails. By being able to spare the rotator cuff and avoid the radial nerve distally, the implementation of helical plates might overcome the downsides of common fixation methods. The aims of the current study were (1) to explore the biomechanical competence of different plate designs and (2) to compare their performance versus the alternative treatment option of using intramedullary nails. Materials and Methods: Twenty-four artificial humeri were assigned to the following four groups for simulation of an unstable proximal humeral shaft fracture and instrumentation: Group 1 (Straight-PHILOS), Group 2 (MULTILOC-Nail), Group 3 (45°-Helical-PHILOS), and Group 4 (90°-Helical-PHILOS). All specimens underwent non-destructive, quasi-static biomechanical testing under loading in axial compression, torsion in internal/external rotation, and pure bending in four directions, accompanied by motion tracking. Results: Axial stiffness/displacement in Group 2 was significantly higher/smaller than in all other groups (p ≤ 0.010). Torsional displacement in Group 2 was significantly bigger than in all other groups (p ≤ 0.017). Significantly smaller coronal plane displacement was identified in Group 2 versus all other groups (p < 0.001) and in Group 4 versus Group 1 (p = 0.022). Significantly bigger sagittal plane displacement was detected in Group 4 versus all other groups (p ≤ 0.024) and in Group 1 versus Group 2 (p < 0.001). Conclusions: Intramedullary nails demonstrated higher axial stiffness and smaller axial interfragmentary movements compared with all investigated plate designs. However, they were associated with bigger torsional movements at the fracture site. Although 90°-helical plates revealed bigger interfragmentary movements in the sagittal plane, they demonstrated improved resistance against displacements in the coronal plane when compared with straight lateral plates. In addition, 45°-helical plates manifested similar biomechanical competence to straight plates and may be considered a valid alternative to the latter from a biomechanical standpoint.

A Pilot Experiment to Measure the Initial Mechanical Stability of the Femoral Head Implant in a Cadaveric Model of Osteonecrosis of Femoral Head Involving up to 50% of the Remaining Femoral Head

Background and Objectives: Currently, only patients with osteonecrosis of the femoral head (ONFH), who had bone defects involving 30–33.3% of the remaining femoral head, are indicated in hip resurfacing arthroplasty (HRA). In an experimental cadaver model of ONFH involving up to 50% of the remaining femoral head, the initial stability of the femoral head implant (FHI) at the interface between the implant and the remaining femoral head was measured. Materials and Methods: The ten specimens and the remaining ten served as the experimental group and the control group, respectively. We examined the degree of the displacement of the FHI, the bonding strength between the FHI and the retained bone and that at the interface between the FHI and bone cement. Results: Changes in the degree of displacement at the final phase from the initial phase were calculated as 0.089 ± 0.036 mm in the experimental group and 0.083 ± 0.056 mm in the control group. However, this difference reached no statistical significance (p = 0.7789). Overall, there was an increase in the degree of displacement due to the loading stress, with increased loading cycles in both groups. In cycles of up to 6000 times, there was a steep increase. After cycles of 8000 times, however, there was a gradual increase. Moreover, in cycles of up to 8000 times, there was an increase in the difference in the degree of displacement due to the loading stress between the two groups. After cycles of 8000 times, however, such difference remained almost unchanged. Conclusions: In conclusion, orthopedic surgeons could consider performing the HRA in patients with ONFH where the bone defects involved up to 50% of the remaining femoral head, without involving the femoral head–neck junction in the anterior and superior area of the femoral head. However, more evidence-based studies are warranted to justify our results.

Treatment of Refractory Congenital Pseudoarthrosis of Tibia with Contralateral Vascularized Fibular Bone Graft and Anatomic Distal Tibial Locking Plate: A Case Series and Literature Review

Background: Congenital pseudoarthrosis of the tibia (CPT) remains a challenge for physicians. Several treatment options have been proposed, but the standard of care remains inconclusive. In this study, we present three patients for whom the failure of prior treatments was managed with a contralateral vascularized fibular bone graft (VFG) and an anatomic distal tibial locking plate. Methods: Between 2017 and 2021, three patients were referred for failed treatment of CPT. All patients had undergone multiple prior surgeries, including tumor excision and fixation with ring external fixators, plates, and screws. We performed radical tumor resection and reconstruction of bone defects with a VFG. The construct was fixed with an anatomic locking plate, and the patients were followed up for a mean of 45.7 months. Results: All three patients were able to obtain graft union at 19.3 weeks. At the final follow-up, all grafts achieved bony hypertrophy without evidence of bone resorption or local tumor recurrence. There was a mean leg length difference of 8.5 cm preoperatively, compared with 6.3 cm postoperatively. The average lower leg angulation was 7.4 degrees and the average ankle range of motion was 58.3 degrees. The mean VAS score was 0 and the mean AOFAS score was 88.3. No significant complications were noted. Conclusions: Implantation of a VFG and an anatomic distal tibia locking plate can be considered an option for treatment-refractory CPT. Patients can expect to achieve bone consolidation, ambulate as tolerated, and have a low complication rate.

Mechanical comparison of standard interlocking, clawed, and expandable wedge locked nail fixations: An experimental and numerical study

INTRODUCTION

Intramedullary nailing has been used as a standard in the treatment of the long bone fractures with its clinical and mechanical advantages. However, using distal locking screws has been associated with longer operative times, higher radiation exposure rates, and complications like breakages of distal screw or nail at the screw hole level. Therefore, attempts to eliminate distal locking screws has been always present for intramedullary nail fixation. With a similar purpose, the present study has been carried out to compare mechanical behaviors of intramedullary nail fixations with different distal locking elements.

MATERIALS AND METHODS

In this study, mechanical behaviors of standard interlocking and clawed nail fixations were compared experimentally in the first part. Six fourth generation Sawbones femurs, which have a simulated subtrochanteric fracture, were divided equally and were fixed with standard interlocking and clawed nails. During axial compression tests, experimental strain measurements were taken from all fixations. After validation of numerical models with using experimental strains and stiffnesses, mechanical behaviors of standard interlocking, clawed, and wedge locked nail fixations were compared numerically under axial compression loads. In numerical comparison, the stress-strain distributions were evaluated.

RESULTS

Experimental results showed that although that there was no significant difference in stiffnesses, standard nail fixation bore two times higher loads than clawed nail fixations. Under loading, decrease in the distance between fracture surfaces was approximately seven times higher in the clawed nail fixation when compared to standard nail fixations. Numerical results showed that wedge locked nail fixation provided equivalent mechanical behavior to standard interlocking nail.

DISCUSSION

In experiments of clawed nail fixation, the high decrease in the distance between fracture surfaces was evidence of the slippage of nail in the medullary canal. For a safe fixation, claws should be deployed when they are completely in contact with the cortical bone, they should be stuck into the bone in a fair amount, and the deployment in the distal third of the femur should be avoided. According to experimentally validated numerical analyses, wedge locked nail fixation may be an alternative for standard interlocking nail fixation if experimental studies support the present results.

Can Locked Fibula Nail Replace Plate Fixation for Treatment of Acute Ankle Fracture? A Systematic Review and Meta-Analysis

The standard surgical treatment for unstable ankle fractures involves open reduction and internal fixation (ORIF) with plates. However, ORIF has been associated with several complications, such as soft tissue irritation, wound infection, and nerve injury. Previous studies have shown that closed reduction and internal fixation with locked intramedullary nails (LIMNs) yields satisfactory efficacy in the treatment of ankle fractures and is associated with low complication rates. Therefore, a systematic review and meta-analysis of randomized controlled trials is imperative to provide evidence on whether or not LIMN fixation is comparable to or superior than traditional ORIF. We conducted a comprehensive literature search in the PubMed, Cochrane Library and EMBASE databases. A total of 4 randomized controlled trials involving 359 participants who suffered ankle fractures were included in this systematic review and meta-analysis. The results showed that the LIMN fixation group was statistically significant in terms of functional outcomes at the 3-month follow-up and wound-related complications. There was no statistical advantage for patients in the LIMN fixation group in terms of nonwound-related complications, total complications, or mid-term follow-up functional outcomes. There was no statistical difference between the LIMN and ORIF groups regarding operation time and quality of reduction. We believe LIMN fixation is a viable option for the treatment of unstable ankle fractures in both young and elderly individuals.

The osteogenetic activities of mesenchymal stem cells in response to Mg2+ ions and inflammatory cytokines: a numerical approach using fuzzy logic controllers

Magnesium (Mg²⁺) ions are frequently reported to regulate osteogenic activities of mesenchymal stem cells (MSCs). In this study, we propose a numerical model to study the regulatory importance of Mg²⁺ ions on MSCs osteoblastic differentiation in the presence of an inflammatory response. A fuzzy logic controller was formulated to receive the concentrations of Mg²⁺ ions and the inflammatory cytokines of TNF-α, IL-10, IL-1β, and IL-8 as cellular inputs and predict the cells’ early and late differentiation rates. Five sets of empirical data obtained from published cell culture experiments were used to calibrate the model. The model successfully reproduced the empirical data regarding the concentration- and phase-dependent effect of Mg²⁺ ions on the differentiation process. In agreement with the experiments, the model showed the stimulatory role of Mg²⁺ ions on the early differentiation phase, once administered at low concentration, and their inhibitory role on the late differentiation phase. The numerical approach used in this study suggested 6–8 mM as the most effective concentration of Mg²⁺ ions in promoting the early differentiation process. Also, the proposed model sheds light on the fundamental differences in the behavioral properties of cells cultured in different experiments, e.g. differentiation rate and the sensitivity of the cultured cells to stimulatory signals such as Mg²⁺ ions. Thus, it can be used to interpret and compare different empirical findings. Moreover, the model successfully reproduced the nonlinearities in the concentration-dependent role of the inflammatory cytokines in early and late differentiation rates. Overall, the proposed model can be employed in studying the osteogenic properties of Mg-based implants in the presence of an inflammatory response.

Magnesium (Mg) is an attractive material for bone implants as it fully degrades after implantation, saving pain and cost of the second surgery for implant removal. To advance its application in the orthopedic industry, it is paramount to fully understand the biological impact of the degradation products, in particular Mg²⁺ ions. Here, we propose a computer model to study the effects of Mg²⁺ ions on bone regeneration. The model focuses on stem cells and includes both the direct stimulation effects of Mg²⁺ ions on cells and the indirect stimulus through the inflammatory system. The proposed model successfully reproduced the experimental data of five different studies. The model additionally highlighted differences amongst different experiments in terms of the cellular response to Mg²⁺ ions. The proposed system therefore provides an important addition to the field of Mg implant research.

Functionally graded additive manufacturing for orthopedic applications

Background

Additive Manufacturing due to its benefits in developing parts with complex geometries and shapes, has evolved as an alternate manufacturing process to develop implants with desired properties. The structure of human bones being anisotropic in nature is biologically functionally graded i,e. The structure possesses different properties in different directions. Therefore, various orthopedic implants such as knee, hip and other bone plates, if functionally graded can perform better. In this context, the development of functionally graded (FG) parts for orthopedic application with tailored anisotropic properties has become easier through the use of additive manufacturing (AM).

Objectives

and Rationale: The current paper aims to study the various aspects of additively manufactured FG parts for orthopedic applications. It presents the details of various orthopedic implants such as knee, hip and other bone plates in a structured manner. A systematic literature review is conducted to study the various material and functional aspects of functionally graded parts for orthopedic applications. A section is also dedicated to discuss the mechanical properties of functionally graded parts.

Conclusion

The literature revealed that additive manufacturing can provide lot of opportunities for development of functionally graded orthopedic implants with improved properties and durability. Further, the effect of various FG parameters on the mechanical behavior of these implants needs to be studied in detail. Also, with the advent of various AM technologies, the functional grading can be achieved by various means e.g. density, porosity, microstructure, composition, etc. By varying the AM parameters. However, the current limitations of cost and material biocompatibility prevent the widespread exploitation of AM technologies for various orthopedic applications.

Experimental testing of fracture fixation plates: A review

Metal and its alloys have been predominantly used in fracture fixation for centuries, but new materials such as composites and polymers have begun to see clinical use for fracture fixation during the past couple of decades. Along with the emerging of new materials, tribological issues, especially debris, have become a growing concern for fracture fixation plates. This article for the first time systematically reviews the most recent biomechanical research, with a focus on experimental testing, of those plates within ScienceDirect and PubMed databases. Based on the search criteria, a total of 5449 papers were retrieved, which were then further filtered to exclude nonrelevant, duplicate or non-accessible full article papers. In the end, a total of 83 papers were reviewed. In experimental testing plates, screws and simulated bones or cadaver bones are employed to build a fixation construct in order to test the strength and stability of different plate and screw configurations. The test set-up conditions and conclusions are well documented and summarised here, including fracture gap size, types of bones deployed, as well as the applied load, test speed and test ending criteria. However, research on long term plate usage was very limited. It is also discovered that there is very limited experimental research around the tribological behaviour particularly on the debris’ generation, collection and characterisation. In addition, there is no identified standard studying debris of fracture fixation plate. Therefore, the authors suggested the generation of a suite of tribological testing standards on fracture fixation plate and screws in the aim to answer key questions around the debris from fracture fixation plate of new materials or new design and ultimately to provide an insight on how to reduce the risks of debris-related osteolysis, inflammation and aseptic loosening.

Deformation of the Titanium Plate Stabilizing the Lateral Ankle Fracture Due to Its Overloading in Case of the Young, Obese Patient: Case Report Including the Biomechanical Analysis

The number of overweight and obese patients in developed countries is gradually increasing. It was reported that 1287 (64%) out of 2007 adults operated on in 2017 had a body mass index (BMI) greater than 25 kg/m2, and 26.4% even greater than 30, while the BMI of the most obese patient was as high as 57.6 kg/m2. Such distressing statistics raised an issue related to the inadequate durability of implants used for the fixation of bone fractures. Implants for the lower-extremity fractures may not be durable enough to fit the requirements of overweight and obese patients. This case report presents the history of a 23-year-old obese male with a BMI of 38.7, who bent the angularly stabile titanium plate stabilizing his broken lateral ankle and torn distal tibiofibular syndesmosis. Biomechanical analysis showed that the maximal static bending moment registered during one-leg standing was equal to 1.55 Nm. This value was circa one-third of the maximally admissible bending moment for this particular plate (5.34 Nm) that could be transmitted without its plastic deformation. Since dynamic forces exceed static ones several (3–12) times during typical activities, such as walking, climbing the stairs, running, and jumping, unpredictable forces may occur and increase the risk of loosening, bending, and even breaking implants. None of these situations should have occurred for the typical patient’s body mass of 75 kg, or even for the analyzed mass of the young patient (120 kg) who tried to avoid excessive loading during his daily routine. Subsequent implant bending and destabilization of the fracture shows that for the significantly high and still growing number of obese patients, a very strict physical regime should be recommended to prevent overabundant dynamic loads. On the other hand, the geometry of implants dedicated to these patients should be reconsidered.

Novel Retrograde Tibial Intramedullary Nailing for Distal Tibial Fractures

Purpose

Postoperative distal tibial fractures are often associated with complications such as difficulties in fracture healing and surgical incision infection. The purpose of this study is to evaluate the fracture healing time and functional recovery after a retrograde tibial intramedullary nail treatment for distal tibial fractures.

Methods

We retrospectively studied 9 cases of patients with distal tibial fractures treated with retrograde intramedullary nailing (IMN). Fracture healing time was based on monthly postoperative x-ray imaging results, and functional outcomes were defined according to the American Orthopaedic Foot and Ankle Society (AOFAS) ankle-hindfoot score.

Results

Among the 9 patients with distal tibial fractures from July 2020 to April 2021, the mean age was 51.8 ± 13.8 years. The classification of distal tibial fractures in the 9 patients according to OTA (Orthopaedic Trauma Association) includes 6 extra-articular fractures (3 of type A1, 2 of type A2, and 1 of type A3) and 3 intra-articular fractures (1 of type C1 and 2 of type C2). Among them, there were 5 closed fracture cases and 4 open fracture cases (according to Gustilo classification: 2 of type I, 2 of type II). We treated the fractures surgically with new retrograde tibial intramedullary nailing. The mean follow-up time for this group was 7.9 months (5–12 months). According to monthly postoperative radiographs performed to monitor fracture healing, the mean healing time was 3.3 months (3–4 months). Final postoperative function according to the AOFAS ankle-hindfoot score shows 6 excellent cases, 3 good cases. No serious complications such as postoperative infection, bone and internal fixation exposure, osteofascial compartment syndrome, or vascular nerve injury occurred.

Conclusion

The new retrograde tibial intramedullary nail (RTN) has some unique advantages, and its treatment of distal tibial fractures can achieve good efficacy, but further studies are still needed to verify it.

Optimal Design and Biomechanical Analysis of a Biomimetic Lightweight Design Plate for Distal Tibial Fractures: A Finite Element Analysis

The treatment of fractures of the distal tibia can be problematic due to the insubstantial soft-tissue covering this part of the anatomy. This study investigates a novel strategy for minimally invasive plate osteosynthesis of distal tibia fractures called bionic lightweight design plating. Following the structure of the animal trabecular bone, we utilized topological mathematical methods to redesign the material layout of the internal fixation device to fulfill the desired lightweight design within given boundary conditions. The results showed that this method can maintain the same stability of the construct as the original plate after a reduction in the original volume by 30%, and the differences in strain energy of plates and maximum node displacement of constructs between the constructs [RP construct vs. LP construct] were not statistically significant (p > 0.05). In the safety assessment of the constructs, the peak stress of plates between constructs was found to not be statistically significantly different under a doubled physiological load (p > 0.05). The average stress of the plates’ elements exceeding the allowable stress was analyzed, and no statistically significant differences were found between the two constructs under axial compression stress conditions (p > 0.05). The average stress of the plates’ elements in the redesigned plating construct under torsional stress conditions was 3.08% less than that of the locked plating construct (p < 0.05). Under the double physiological load condition, 89% of the elements of the plate in the redesigned plating construct and 85% of the elements of the plate in the locked plating construct were lower than the maximum safe stress of the plate, which was 410 MPa (secondary allowable stresses). That reminds us the topology optimization offer a possible way to improve the capacity of soft tissue protection while ensuring the safety of the RP construct by reducing the volume of the implants.

Osteosynthesis of diaphyseal tibia fracture with locking compression plates: A numerical investigation using Taguchi and ANOVA

Performance of the locking compression plate (LCP) is a multifactorial function. The control parameters of plating, such as geometries, material properties, and physical constraints of the LCP components, affect basic functions associated with the bone fixation, including the extent of stress shielding and subsequent bone remodeling, strength and stability of the bone-LCP construct, and performance of secondary bone healing. The main objectives of this research were as follows: (1) to find the appropriate values of control parameters of an LCP construct to achieve the optimized performance throughout bone healing; and (2) to unravel relationships between LCP parameters and the LCP's performance. Different values for the plate/screw modulus of elasticity (E), plate width (W), plate thickness (T), screw diameter (D), bone-plate offset (O), and screw configuration (C), as six control parameters, were considered at five different levels. Taguchi method was adopted to create trial combinations of control parameters and determining the best set of parameters, which can optimize the overall performance of the LCP. All design cases were analyzed using the finite element method. The optimal set of control parameters consisting of 150 GPa, 12 mm, 4 mm, 5.5 mm, 2 mm, and 123,678 were determined for E, W, T, D, O, and C, respectively. Furthermore, ANOVA was used to rank the most influential parameters on each function of the LCP fixation. In the overall performance of the LCP fixation, E, D, T, C, W, and O showed a contribution percentage of 46%, 22%, 10%, 11%, 8%, and 3%, respectively.

Optimization of Connecting Rod Design Parameters for External Fixation System: A Biomechanical Study

The role of connecting rod in healing process of a fractured bone has always been of significant importance for surgeons. Adding a connecting rod to the fixator would be a secure option for increasing stability without increasing infection rate. The roles of 4 design parameters of the connecting rod (ie, connecting rod diameter, elevation, material, and configuration) were assessed by using finite element models to calculate axial stiffness and interfragmentary strain at the fracture gap. Taguchi method was used to achieve an optimal design set for maximizing stability with regard to connecting rod variables. Also, analysis of variance (ANOVA) approach was employed to determine contribution percentage of each design parameter on outputs. For optimizing connecting rod design parameters, an optimal set of variables consisting of 11 mm, 40 mm, 200 GPa, and Type 3 external fixator were determined by Taguchi for connecting rod diameter, elevation, modulus of elasticity, and configuration, respectively. However, as Type 3 external fixator stability is a little more than Type 2, it would be better if Type 3 external fixator in Taguchi suggestion be replaced by Type 2 external fixator to be as minimally invasive as possible. Furthermore, ANOVA results revealed that the connecting rod configuration is the most important parameter with 95% and 96% effectiveness on the interfragmentary strain and axial stiffness.

Strategies to Improve Bone Healing: Innovative Surgical Implants Meet Nano-/Micro-Topography of Bone Scaffolds

Successful fracture healing is dependent on an optimal mechanical and biological environment at the fracture site. Disturbances in fracture healing (non-union) or even critical size bone defects, where void volume is larger than the self-healing capacity of bone tissue, are great challenges for orthopedic surgeons. To address these challenges, new surgical implant concepts have been recently developed to optimize mechanical conditions. First, this review article discusses the mechanical environment on bone and fracture healing. In this context, a new implant concept, variable fixation technology, is introduced. This implant has the unique ability to change its mechanical properties from “rigid” to “dynamic” over the time of fracture healing. This leads to increased callus formation, a more homogeneous callus distribution and thus improved fracture healing. Second, recent advances in the nano- and micro-topography of bone scaffolds for guiding osteoinduction will be reviewed, particularly emphasizing the mimicry of natural bone. We summarize that an optimal scaffold should comprise micropores of 50–150 µm diameter allowing vascularization and migration of stem cells as well as nanotopographical osteoinductive cues, preferably pores of 30 nm diameter. Next to osteoinduction, such nano- and micro-topographical cues may also reduce inflammation and possess an antibacterial activity to further promote bone regeneration.

Treatment of Distal Metaphyseal Tibial Fractures with Anterolateral Plates or with Anterolateral-Medial Plates: A Retrospective Series

Distal metaphyseal tibial fractures (3-5 cm from the joint with zones of comminution or <3 cm from the joint) are challenging to fix and are associated with many complications. The study objective was to evaluate the functional outcomes and complications after treating distal metaphyseal tibial fractures using anatomical anterolateral tibia locking plates or anterolateral-medial plates. This retrospective study included 57 patients with distal metaphyseal tibial fractures. Thirty patients were treated by open reduction internal fixation with anterolateral plates; 27 patients were treated with anterolateral-medial plates. Patients were followed at regular intervals. The time to fracture union and complications were recorded. We evaluated the stage of fracture healing using the Radiographic Union Score for Tibial fractures. The patients treated with anterolateral plates had significantly higher rates of loss of reduction and malunion than those treated with anterolateral-medial plates (p = .02 and p = .002, respectively). There were no significant differences in the radiographic union scores (p = .22), non-union (p = .17), incision necrosis (p = .91), or infection (p = .94) between the 2 groups. The functional outcomes were assessed using the American Orthopedic Foot and Ankle Society hindfoot-ankle score at the 12-month follow-up. The mean hindfoot-ankle scores were 90.9 ± 5.0 (range 79 to 100, median 90) and 92.3 ± 5.1 (range 82 to 100, median 92) for the anterolateral plates and anterolateral-medial plates, respectively (p = .29). For distal metaphyseal tibial fractures, anterolateral-medial plates may be worthwhile for reducing loss of reduction and malunion.

The role of mechanical stimulation in the enhancement of bone healing

The biomechanical environment plays a dominant role in the process of fracture repair. Mechanical signals control biological activities at the fracture site, regulate the formation and proliferation of different cell types, and are responsible for the formation of connective tissues and the consolidation of the fractured bone. The mechanobiology at the fracture site can be easily manipulated by the design and configuration of the fracture fixation construct and by the loading of the extremity (weight-bearing prescription). Depending on the choice of fracture fixation, the healing response can be directed towards direct healing or towards indirect healing through callus formation. This manuscript summarizes the evidence from experimental studies and clinical observations on the effect of mechanical manipulation on the healing response. Parameters like fracture gap size, interfragmentary movement, interfragmentary strain, and axial and shear deformation will be explored with respect to their respective effects on fracture repair. Also, the role of externally applied movement on the potential enhancement on the fracture repair process will be explored. Factors like fracture gap size, type and amplitude of the mechanical deformation as well as the loading history and its timing will be discussed.

A novel design of printable tunable stiffness metamaterial for bone healing

A tunable stiffness bone rod was designed, optimized, and 3D printed to address the shortcomings of existing bone fixation devices, such as stress shielding and bone nonunion in the healing of fractured bones. Current bone plates/rods have constant and high stiffness. High initial stiffness prevents the micromotion of newly formed bone and results in poor bone healing. Our novel design framework provides surgeons with a ready-for-3D-printing, patient-specific design, optimized to have the desired force-displacement response with a stopping mechanism for preventing further deformation under higher-than-normal loads, such as falling. The computational framework is a design optimization based on the multi-objective genetic algorithm (GA) optimization with the FE simulation to quantify the objectives: tuning the varied stiffness while minimizing the maximum von Mises stress of the model to avoid plastic and permanent deformation of the bone rod. The computational framework for optimum design of tunable stiffness metamaterial presented in this paper is not specific for a tibia bone rod, and it can be used for any application where bilinear stiffness is desirable.

A mechanobiological approach to find the optimal thickness for the locking compression plate: Finite element investigations

This study aimed at finding the acceptable range, and the optimal value for the locking compression plate (LCP) thickness (THK), through simulating the osteogenic pathway of bone healing, and by checking bone-plate construct's strength and stability. To attain the goals of this research, a multi-objective approach was adopted, which should trade-off between some conflicting objectives. A finite element model of the long bone-plate construct was made first, and validated against an experimental study. The validated model was then employed to determine the initial strength and stability of the bone-plate construct, for the time right after surgery, for various thicknesses of the LCP. Afterward, coupling with a mechano-regulatory algorithm, the iterative process of bone healing was simulated, and follow up was made for each LCP thickness, over the first 16 post-operative weeks. Results of this study regarding the sequence of tissue evolution inside the fracture gap, showed a similar trend with the existing in-vivo data. For the material and structural properties assigned to the bone-plate construct, in this study, an optimal thickness for the LCP was found to be 4.7 mm, which provides an enduring fixation through secondary healing, whereas for an LCP with a smaller or greater thickness, either bone-implant failure, unstable fixation, impaired fracture consolidation, or primary healing may occur. This result is in agreement with a recent study, that has employed a comprehensive optimization approach to find the optimal thickness.

The biomechanical performance of the night-time Providence brace: experimental and finite element investigations

The main goal of this study was to investigate the performance of a night-time Providence brace, which alters stress distribution in the growth plates and ultimately result in a reduced Cobb angle, from a biomechanical standpoint, using experimental and in-silico tools. A patient with a mild scoliosis (Cobb angle = 17) was chosen for this study. Applied forces from the Providence brace on the patient's rib cage and pelvis were measured using flexible force pads, and the measured forces were then imported to the generated FE model, and their effects on both curvature and stress distribution were observed. The measured mean forces applied by the brace were 29.4 N, 24.7 N, 22.4 N, and 37.6 N in the posterior pelvis, anterior pelvis, superior thorax, and inferior thorax, respectively, in the supine position. Results of the FE model showed that there is curvature overcorrection, and also Cobb angle was reduced from 17°, in the initial configuration, to 3.4° right after using the brace. The stress distribution, resulted from the FE model, in the patient's growth plate with the brace in the supine position, deviates from that of a scoliotic individual without the brace, and was in favor of reducing the Cobb angle. It was observed that by wearing the night time brace, unbalanced stress distribution on the lumbar vertebrae caused by the scoliotic spine's curvatures, can be somehow compensated. The method developed in this study can be employed to optimize existing scoliosis braces from the biomechanical standpoint.

Fixation of distal tibia fracture through plating, nailing, and nailing with Poller screws: A comparative biomechanical-based experimental and numerical investigation

The goal of this study was to investigate two commonly used methods of fixation of distal metaphyseal tibia fractures, plating and nailing as well as the less frequently employed nailing with Poller screws, from a biomechanical perspective. Despite numerous studies, the best method to repair fractures of tibia the remains up for of debate. This study includes an in vitro experimental phase on human cadaveric tibias followed by a finite element analysis. In the experimental phase, under partial weight-bearing axial loading, the axial stiffness of the bone-implant construct and interfragmentary movements for each of the fixation methods, bone-plate, bone-nail, and bone-nail-Poller screw, were measured and compared with each other. Shear interfragmentary movement and stress distribution in the bone-implant construct for the three mentioned fixation methods were also determined from FE models and compared with each other. Results of in vitro experiments, i.e., the exertion of axial loading on the tibia-plate, tibia-nail, and tibia-nail-Poller screw, showed that utilization of tibia-nail and tibia-nail-Poller screw led to a stiffer bone-implant construct, and consequently, lower interfragmentary movement, compared to the tibia-plate construct ( p values for tibia-nail and tibia-nail-Poller screw, and for both axial stiffness and interfragmentary movement, compared to those of tibia-plate construct, were less than 0.05). Numerical analyses showed that nailing produced less undesirable shear interfragmentary movement, compared to the plating, and application of a Poller screw decreased the shear movements, compared to tibia-nail. Furthermore, using the finite element analysis, maximum von Mises stress of adding a screw in tibia-nail, tibia-plate, and tibia-nail-Poller screw, was found to be: 51.5, 78.6, and 60.5 MPa, respectively. The results of this study suggested that from a biomechanical standpoint, nailing both with and without a Poller screw is superior to plating for the treatment of distal tibia fractures.

Intramedullary nailing as an alternative to plate fixation in patients with distal fibular fracture

BACKGROUND

We examined whether the intramedullary nailing (IMN) can be used as an alternative modality to the plate fixation (PF) in patients with distal fibular fracture with displaced fragments.

PATIENTS AND METHODS

The eligible patients of two treatment arms (IMN group: n=30 and the group: n=31) were evaluated at 3, 6, 9 and 12 months postoperatively, for which functional outcome measures include differences in the American Orthopaedic Foot and Ankle Society Scores (AOFAS) and the Olerud Molander Ankle Scores (OMAS) between the two groups. In addition, radiological outcome measures include differences in radiological outcome scores at 12 months between the two groups. Differences in the percentage of frequency of postoperative complications between the two groups served as safety outcome measures.

RESULTS

At 3 months, the AOFAS and OMAS were significantly higher in the IMN group as compared with the PF group (p<0.0001 and p=0.0177, respectively). At 6 months, the AOFAS were significantly higher in the IMN group as compared with the PF group (p=0.0255). But there were no significant differences in the OMAS between the two groups (p=0.1077). At 9 and 12 months, there were no significant differences in the AOFAS and OMAS between the two groups (p=0.4334 and 0.3227, respectively at 9 months and p=0.8731 and 0.7610, respectively, at 12 months). These results indicate that the IMN group achieved a faster recovery as compared with the PF group. At 12 months, the radiological outcome scores were 3.67±0.60 in the IMN group and 3.71±0.52 in the PF group (p=0.7816). All the patients of each group achieved a bony union at 12 months. At 12 months, the percentage of frequency of postoperative complications was significantly lower in the IMN group as compared with the PF group (p=0.0227).

CONCLUSIONS

The IMN might be considered as an alternative surgical modality to the PF in patients with distal fibular fracture with displaced fragments. But further large-scale, multi-center studies are warranted to establish our results.

PREDICTION OF THE TREND OF BONE FRACTURE HEALING BASED ON THE RESULTS OF THE EARLY STAGES SIMULATIONS: A FINITE ELEMENT STUDY

To date, several studies have implied the importance of early stage mechanical stability in the bone fracture healing process. This study aimed at finding a correlation between the predicted different tissue phenotypes in the early stages of healing and the ultimate healing outcome. For this purpose, the process of fracture healing was numerically simulated employing an axisymmetric bi-phasic finite element (FE) model for three initial gap sizes of 1, 3 and 6[Formula: see text]mm and four initial interfragmentary strains (IFS) of 7%, 11%, 15% and 19%. The model was validated with experimental and other numerical studies from the literature. Results of this study showed that the amount of cartilage and fibrous tissue observed in the early stage after fracture can be used to qualitatively assess the outcome of complete bone healing process. Greater amount of cartilage in early stage of healing process yielded faster callus maturation, and delayed maturation of callus was predicted in the case of high fibrous tissue production. Results of this study can be used to provide an estimation of the performance of different fixation systems by considering the amounts of cartilage and fibrous tissues observed in the early stage of healing.

Extreme Nailing: Is It Safe to Allow Immediate Weightbearing After Intramedullary Nail Fixation of Extra-articular Distal Tibial Fractures (OTA/AO 43-A)?

OBJECTIVES

To determine whether immediate weightbearing after intramedullary (IM) fixation of extra-articular distal tibial fractures (OTA/AO 43-A) results in a change in alignment before healing.

DESIGN

Retrospective review.

SETTING

Level 1 trauma center.

INTERVENTION

IM nailing of distal tibial fractures.

PATIENTS/PARTICIPANTS

Fifty-three patients with 54 fractures, all of whom could bear weight as tolerated postoperatively. Eighteen fractures were OTA/AO 43-A1, 20 OTA/AO 43-A2, and 16 OTA/AO 43-A3; 20 fractures were open.

MAIN OUTCOME MEASUREMENTS

Change in fracture alignment or loss of position.

RESULTS

Average change from initial angulation at final follow-up was 0.52 ± 1.49 degrees of valgus and 0.48 ± 3.14 degrees of extension. Final alignment was excellent in 14, acceptable in 28, and poor in 12; 2 fractures went from acceptable initial alignment to poor final alignment; and 2 fractures went from excellent to acceptable alignment. Seven fractures had an improvement in alignment over time. Two fractures required free-flap coverage and 4 required staged grafting because of bone loss. Ten fractures had an unplanned return to the operating room (5 for infected nonunion requiring implant exchange, 3 for infection requiring debridement without implant revision, and 2 for aseptic nonunion). No patient had revision for implant failure.

CONCLUSIONS

Immediate weightbearing after IM fixation of extra-articular distal tibial fractures (OTA/AO 43-A) led to minimal change in alignment and seems to be safe for most patients. Complications were consistent with those reported in previous non-weightbearing cohorts.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Investigation on distal femoral strength and reconstruction failure following curettage and cementation: In-vitro tests with finite element analyses

Cement augmentation following benign bone tumor surgery, i.e. curettage and cementation, is recommended in patients at high risk of fracture. Nonetheless, identifying appropriate cases and devices for augmentation remains debatable. Our goal was to develop a validated biomechanical tool to: predict the post-surgery strength of a femoral bone, assess the precision and accuracy of the predicted strength, and discover the mechanisms of reconstruction failure, with the aim of finding a safe biomechanical fixation. Tumor surgery was mimicked in quantitative-CT (QCT) scanned cadaveric human distal femora, and subsequently tested in compression to measure bone strength (F_Exp). Finite element (FE) models considering bone material non-homogeneity and non-linearity were constructed to predict bone strength (F_FE). Analyses of contact, damage, and crack initiation at the bone-cement interface (BCI) were completed to investigate critical failure locations. Results of paired t-tests did not show a significant difference between F_Exp and F_FE (P > 0.05); linear regression analysis resulted in good correlation between F_Exp and F_FE (R² = 0.94). Evaluation of the models precision using linear regression analysis yielded R² = 0.89, with the slope = 1.08 and intercept = -324.16 N. FE analyses showed the initiation of damage and crack and a larger cement debonding area at the proximal end and most interior part of BCI, respectively. Therefore, we speculated that devices that reinforce critical failure locations offer the most biomechanical advantage. The QCT-based FE method proved to be a reliable tool to predict distal femoral strength, identify some causes of reconstruction failure, and assist in a safer selection of fixation devices to reduce post-operative fracture risk.

Stability of femoral neck fracture fixation: A finite element analysis

Femoral neck fractures represent a relatively uncommon injury in the non-elderly population often resulting from high-energy trauma. Clinical outcome in these patients can be improved by optimizing surgical procedures and selecting appropriate fixation methods. The aim of this study was to develop a numerical fracture model to investigate the influence of critical mechanical factors on the stability of fixation methods for femoral neck fractures. The mechanical stability of fracture fixation was assessed through employing finite element models and simulating progressive consolidation of the fracture for a vertical femoral neck fracture (i.e. Pauwels type III in which the angle between the fracture line and the horizontal plane is greater than 70°). Mechanical performance was compared among three different fixation methods (cannulated screws, dynamic hip screw with de-rotational screw, and proximal femoral locking plate). Axial femoral head displacement varied from 2.3 mm for cannulated screws to 1.12 mm for proximal femoral locking plate, although dynamic hip screw with de-rotational screw indicated a value of 0.94 mm. Considering a consolidated fracture and full weight-bearing load case, average displacements of fracture fragments were obtained of about 1.5, 3 and 70 µm for dynamic hip screw with de-rotational screw, proximal femoral locking plate and cannulated screws methods, respectively. In terms of interfragmentary movements at the fracture site, outcomes of this study demonstrated that, in agreement with our previous experimental research, the dynamic hip screw with de-rotational screw implant is a more effective choice than cannulated screws and proximal femoral locking plate techniques for vertical femoral neck fractures in young patients. Thus, one may conclude that the use of dynamic hip screw with de-rotational screw, particularly during the early stages of bone healing, could provide suitable mechanical environments that facilitate direct bone formation and shorter healing times.

The Great Need of a Biomechanical-Based Approach for Surgical Methods of Giant Cell Tumor: A Critical Review

There are many unanswered questions about giant cell tumor (GCT) treatment and not enough attention is paid to the biomechanics of the current treatment methods. Treatment methods have not changed much, and the best method remains controversial to some degree, due to the lack of adequate clinical and biomechanical investigations. Biomechanical tests, including in vitro mechanical experiments combined with finite element analysis, are very helpful in assessing the efficiency of the surgical methods employed and in determining the optimal method of surgery. Tests can be tailored to meet a patient’s needs, while limiting postoperative complications. One of the complications, following tumor surgery, is the frequency of postoperative fractures. In order to prevent postoperative fractures, defect reconstruction is recommended. The reconstruction usually consists of defect infilling with bone cement, and in the case of large defects cement augmentation is employed. Whether cement augmentation is essential and offers enough mechanical strength and what is the best fixation device for cement augmentation are areas of debate. In this article, the biomechanical studies comparing different methods of tumor surgery and cement augmentation, highlighting the areas needing more attention to advance GCT treatment, are critically reviewed. Based on our review, we recommend a biomechanical criterion for the essence of defect reconstruction, which must include patient specific factors, in addition to the tumor geometrical properties.