Transverse patella fracture fixation: A cadaveric biomechanical comparison of cannulated screws and anterior tension band versus low-profile, multiplanar mesh plating.

INTRODUCTION: Multiplanar mesh plating of patella fractures has become more popular in recent years. It was the goal of this study to compare the biomechanical stability of cannulated screw with anterior tension band to multiplanar mesh plating for fixation of transverse patella fractures in cadaver specimens. MATERIALS AND METHODS: Eight matched pairs of fresh frozen cadaveric knees were obtained and soft tissues dissected leaving the extensor mechanism, joint capsule, and retinaculum intact. Transverse fractures were created at the mid-portion of the patella. For each pair, one specimen was repaired using cannulated screws with anterior tension band, and the second was repaired using multiplanar mesh plating. Each specimen underwent cyclic extension loading with loads increasing by 1.1 kg after every 50 cycles. Interfragmentary displacement was measured at the end of each interval at both 5° and 45° of knee flexion angle, with fixation failure defined by >2 mm displacement. RESULTS: The specimens fixed with multiplanar mesh plating survived more cycles and higher loads than the specimens fixed with cannulated screws with anterior tension band (p = 0.011 comparing survival plots). After 150 cycles of extension loading, 3 of 8 of the specimens fixed with screws/tension band had failed, whereas none of the mesh plated specimens had failed. After 400 cycles, 7 of 8 of the screws/tension band had failed, whereas half of the mesh plated specimens had failed. CONCLUSIONS: While a more technically challenging and expensive technique, mesh plating for patella fractures appears to offer greater durability than traditional cannulated screw with tension banding.

Mechanics of dynamic compression plate application in fracture fixation.

BACKGROUND: Dynamic compression plating is a fundamental type of bone fracture fixation used to generate interfragmentary compression. The goal of this study was to investigate the mechanics of the surgical application of these plates, specifically how plate prebend, screw location, fracture gap, and applied torque influence the resulting compressive pressures. METHODS: Synthetic bones with transverse fractures were fixed with locking compression plates. One side of the fracture was fixed with locking screws. On the other side of the fracture, a nonlocking screw was inserted eccentrically to induce interfragmentary compression. A pressure mapping sensor within the fracture gap was used to record the resulting pressure distribution. Plate prebends of 0 mm, 1.5 mm, and 3 mm were tested. Three locations of the eccentric screw, four levels of screw torque, and two initial fracture gap conditions also were tested. FINDINGS: With increasing plate prebend, fracture compression pressures shifted significantly toward the far cortex; however, compression force decreased (P < 0.05). The 1.5 mm prebend plate resulted in the greatest contact area. Increasing screw torque generally resulted in greater fracture compression force. The introduction of a 1 mm fracture gap at the far cortex prior to dynamic compression resulted in little or no fracture compression. INTERPRETATION: The model showed that increasing plate prebend results in an increasing shift of fracture compression pressures toward the far cortex; however, this is accompanied by decreases in compressive force. Initial fracture gaps at the far cortex can result in little or no compression.

Finite element modeling of fracture compression by compression plates.

Dynamic compression plating is a common type of fracture fixation used to compress between bone fragments. The quality of compression across the fracture is important for postoperative stability and primary bone healing. Compression quality may be affected by surgical variations in plate prebend, screw location, screw torque, fracture gap, and implant material. Computational modeling provides a tool for systematically examining these factors, and for visualizing the mechanisms involved. The purpose of this study was to develop a finite element model of dynamic compression plating that includes screw insertion under torque control, establish model credibility through sensitivity analyses and experimental validation, and use the model to examine the effects of surgical variables on fracture compression and postoperative stability. Model-predicted compressive pressures had good agreement with corresponding synthetic bones experiments under a variety of conditions. Models demonstrated that introducing a 1.5 or 3 mm plate prebend (using a 4.5 mm narrow LCP plate) eliminated gapping at the far cortex, which is consistent with clinical recommendations. However, models also revealed that plate prebend led to sharp decreases in fracture compressive force, exceeding 80% in some cases. A 1.5 mm plate prebend resulted in the most uniform pressures across the fracture. Testing of a simplified model form used in previous computational modeling studies showed large inaccuracies for constructs with plate prebend. This study provides the first experimentally validated computational models of dynamic compression plate fracture fixation, and reveals important effects of plate prebend and fracture gap on fracture compression quality.

Toxicity assessment of CeO2 and CuO nanoparticles at the air-liquid interface using bioinspired condensational particle growth.

CeO2 and CuO nanoparticles (NPs) are used as additives in petrodiesel to enhance engine performance leading to reduced diesel combustion emissions. Despite their benefits, the additive application poses human health concerns by releasing inhalable NPs into the ambient air. In this study, a bioinspired lung cell exposure system, Dosimetric Aerosol in Vitro Inhalation Device (DAVID), was employed for evaluating the toxicity of aerosolized CeO2 and CuO NPs with a short duration of exposure (≤10 min vs. hours in other systems) and without exerting toxicity from non-NP factors. Human epithelial A549 lung cells were cultured and maintained within DAVID at the air-liquid interface (ALI), onto which aerosolized NPs were deposited, and experiments in submerged cells were used for comparison. Exposure of the cells to the CeO2 NPs did not result in detectable IL-8 release, nor did it produce a significant reduction in cell viability based on lactate dehydrogenase (LDH) assay, with a marginal decrease (10%) at the dose of 388 µg/cm2 (273 cm2/cm2). In contrast, exposure to CuO NPs resulted in a concentration dependent reduction in LDH release based on LDH leakage, with 38% reduction in viability at the highest dose of 52 µg/cm2 (28.3 cm2/cm2). Cells exposed to CuO NPs resulted in a dose dependent cellular membrane toxicity and expressed IL-8 secretion at a global dose five times lower than cells exposed under submerged conditions. However, when comparing the ALI results at the local cellular dose of CuO NPs to the submerged results, the IL-8 secretion was similar. In this study, we demonstrated DAVID as a new exposure tool that helps evaluate aerosol toxicity in simulated lung environment. Our results also highlight the necessity in choosing the right assay endpoints for the given exposure scenario, e.g., LDH for ALI and Deep Blue for submerged conditions for cell viability.

Cannabidiol and Cannabigerol, Nonpsychotropic Cannabinoids, as Analgesics that Effectively Manage Bone Fracture Pain and Promote Healing in Mice.

Bone fractures are among the most prevalent musculoskeletal injuries, and pain management is an essential part of fracture treatment. Fractures heal through an early inflammatory phase, followed by repair and remodeling. Nonsteroidal anti-inflammatory drugs (NSAIDs) are not recommended for fracture pain control as they potently inhibit the inflammatory phase and, thus, impair the healing. Opioids do not provide a better alternative for several reasons, including abuse potential. Accordingly, there is an unmet clinical need for analgesics that effectively ameliorate postfracture pain without impeding the healing. Here, we investigated the analgesic efficacy of two nonpsychotropic cannabinoids, cannabidiol (CBD) and cannabigerol (CBG), in a mouse model for tibial fracture. Mice with fractured tibiae exhibited increased sensitivity to mechanical, cold, and hot stimuli. Both CBD and CBG normalized pain sensitivity to all tested stimuli, and their analgesic effects were comparable to those of the NSAIDs. Interestingly, CBD and CBG promoted bone healing via multiple mechanisms during the early and late phases. During the early inflammatory phase, both cannabinoids increased the abundance of periosteal bone progenitors in the healing hematoma and promoted the osteogenic commitment of these progenitors. During the later phases of healing, CBD and CBG accelerated the fibrocartilaginous callus mineralization and enhanced the viability and proliferation of bone and bone-marrow cells. These effects culminated in higher bone volume fraction, higher bone mineral density, and improved mechanical quality of the newly formed bone. Together, our data suggest CBD and CBG as therapeutic agents that can replace NSAIDs in managing postfracture pain as both cannabinoids exert potent analgesic effects and, at the same time, promote bone healing. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Assessment of Scanning Mobility Particle Sizer (SMPS) for online monitoring of delivered dose in an in vitro aerosol exposure system.

Real-time monitoring of dosimetry is critical to mitigating the constraints of offline measurements. To address this need, the use of the Scanning Mobility Particle Sizer (SMPS) to estimate the dose delivered through the Dosimetric Aerosol in Vitro Inhalation Device (DAVID) was assessed. CuO nanoparticles suspended in ethanol at different concentrations (0.01-10 mg/mL) were aerosolized using a Collison nebulizer and diluted with air at a ratio of either 1:3 (setup 1) or 1:18 (setup 2). From the aerosol volume concentrations measured by the SMPS, density of CuO (6.4 g/cm3), collection time (5-30 min), flow rate (0.5 LPM) and deposition area (0.28 cm2), the mass doses (DoseSMPS) were observed to increase exponentially over time and ranged from 0.02 ± 0.001 to 84.75 ± 3.49 µg/cm2. The doses calculated from the Cu concentrations determined by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) (DoseICP) also increased exponentially over time (0.01 ± 0.01-97.25 ± 1.30 µg/cm2). Regression analysis between DoseICP and DoseSMPS showed R2 ≥ 0.90 for 0.1-10 mg/mL. As demonstrated, the SMPS can be used to monitor the delivered dose in real-time, and controlled delivery of mass doses with a 226-fold range can be attained in ≤30 min in DAVID by adjusting the nebulizer concentration, dilution air and time.

Assessment of Bone Fracture Healing Using Micro-Computed Tomography.

Micro-computed tomography (µCT) is the most common imaging modality to characterize the three-dimensional (3D) morphology of bone and newly formed bone during fracture healing in translational science investigations. Studies of long bone fracture healing in rodents typically involve secondary healing and the formation of a mineralized callus. The shape of the callus formed and the density of the newly formed bone may vary substantially between timepoints and treatments. Whereas standard methodologies for quantifying parameters of intact cortical and trabecular bone are widely used and embedded in commercially available software, there is a lack of consensus on procedures for analyzing the healing callus. The purpose of this work is to describe a standardized protocol that quantitates bone volume fraction and callus mineral density in the healing callus. The protocol describes different parameters that should be considered during imaging and analysis, including sample alignment during imaging, the size of the volume of interest, and the number of slices that are contoured to define the callus.

Comparison ofin-situversusex-situdelivery of polyethylenimine-BMP-2 polyplexes for rat calvarial defect repair via intraoperative bioprinting.

Gene therapeutic applications combined with bio- and nano-materials have been used to address current shortcomings in bone tissue engineering due to their feasibility, safety and potential capability for clinical translation. Delivery of non-viral vectors can be altered using gene-activated matrices to improve their efficacy to repair bone defects.Ex-situandin-situdelivery strategies are the most used methods for bone therapy, which have never been directly compared for their potency to repair critical-sized bone defects. In this regard, we first time explore the delivery of polyethylenimine (PEI) complexed plasmid DNA encoding bone morphogenetic protein-2 (PEI-pBMP-2) using the two delivery strategies,ex-situandin-situdelivery. To realize these gene delivery strategies, we employed intraoperative bioprinting (IOB), enabling us to 3D bioprint bone tissue constructs directly into defect sites in a surgical setting. Here, we demonstrated IOB of an osteogenic bioink loaded with PEI-pBMP-2 for thein-situdelivery approach, and PEI-pBMP-2 transfected rat bone marrow mesenchymal stem cells laden bioink for theex-situdelivery approach as alternative delivery strategies. We found thatin-situdelivery of PEI-pBMP-2 significantly improved bone tissue formation compared toex-situdelivery. Despite debates amongst individual advantages and disadvantages ofex-situandin-situdelivery strategies, our results ruled in favor of thein-situdelivery strategy, which could be desirable to use for future clinical applications.

Biomechanical Comparison of Fiber Tape Device Versus Transarticular Screws for Ligamentous Lisfranc Injury in a Cadaveric Model.

BACKGROUND: The preferred method of fixation and surgical treatment for ligamentous Lisfranc injuries is controversial. Transarticular screws, bridge plating, fusion, and flexible fixation have been described, yet none have demonstrated superiority. Furthermore, screw fixation and plating often require secondary surgery to remove implants, leading surgeons to seek alternative fixation methods. PURPOSE: To compare transarticular screws and a fiber tape construct under a spectrum of biomechanical loads by evaluating the diastasis at 3 joints in the Lisfranc complex. STUDY DESIGN: Controlled laboratory study. METHODS: Eight matched pairs of fresh, previously frozen lower extremity cadaveric specimens were fixed with either 2 cannulated transarticular crossed screws or a fiber tape construct with a supplemental intercuneiform limb. The diastasis between bones was measured at 3 midfoot joints in the Lisfranc complex: the Lisfranc articulation, the second tarsometatarsal joint, and the intercuneiform joint. Measurements were obtained for the preinjured, injured, and fixation conditions under static loading at 50% donor body weight. Specimens then underwent cyclic loading performed at 1 Hz and 100 cycles, based on 100-N stepwise increases in ground-reaction force from 100 to 2000 N, to simulate postoperative loading from the partial weightbearing stage to high-energy activities. Failure of fixation was defined as diastasis ≥2 mm at the Lisfranc articulation (second metatarsal-medial cuneiform joint). RESULTS: There were no significant differences in diastasis detected at the Lisfranc articulation or the intercuneiform joint throughout all loading cycles between groups. All specimens endured loading up to 50% body weight + 1400 N. Up to and including this stage, there were 2 failures in the cannulated transarticular crossed-screw group and none in the fiber tape group. CONCLUSION: The fiber tape construct with a supplemental intercuneiform limb, which does not require later removal, may provide comparable biomechanical stability to cannulated transarticular crossed screws, even at higher loads. CLINICAL RELEVANCE: Ligamentous Lisfranc injuries are common among athletes. Therefore, biomechanical evaluations are necessary to determine stable constructs that can limit the time to return to play. This study compares the biomechanical stability of 2 methods of fixation for ligamentous injury through a wide spectrum of loading, including those experienced by athletes.

The effect of cigarette smoke versus vaporized nicotine on healing of a rat femur.

INTRODUCTION: Little data exists regarding the effects of vaporized nicotine on healing. Our goal was to compare vaporized nicotine, combusted nicotine and control with respect to bone healing in a rat femur fracture model. MATERIALS AND METHODS: Forty-five male Sprague Dawley rats were divided into three equal cohorts. Rats were exposed to two cigarettes daily, an equivalent dose of vaporized nicotine, or control, six days a week. Exposures occurred for 4 weeks prior to iatrogenic femur fracture and intramedullary repair. Four additional weeks of exposure occurred prior to sacrifice. Radiographic, biomechanical and histologic analysis was conducted. RESULTS: No significant difference between the three groups was identified for total mineralized bone volume (p = 0.14), total volume of mature bone (p = 0.12) or immature bone (p = 0.15). Importantly, less total mineralized bone volume and immature bone volume was seen in the vaporized nicotine group compared to combusted tobacco, but results were not significant. Biomechanical testing revealed no significant difference in group torsional stiffness (p = 0.92) or maximum torque (p = 0.31) between the three groups. On histologic analysis, chi-square testing showed no significant difference in any category. CONCLUSIONS: This exploratory study compared combusted nicotine, vaporized nicotine and a control on rat femur fractures. While no statistically significant differences were identified, there were trends showing less total mineralized bone volume and immature bone volume in the vaporized nicotine group compared to the other groups. Additional study is warranted based on our findings.

Controlled Co-delivery of pPDGF-B and pBMP-2 from intraoperatively bioprinted bone constructs improves the repair of calvarial defects in rats.

Intraoperative bioprinting (IOB), which refers to the bioprinting process performed on a live subject in a surgical setting, has made it feasible to directly deliver gene-activated matrices into craniomaxillofacial (CMF) defect sites. In this study, we demonstrated a novel approach to overcome the current limitations of traditionally fabricated non-viral gene delivery systems through direct IOB of bone constructs into defect sites. We used a controlled co-delivery release of growth factors from a gene-activated matrix (an osteogenic bioink loaded with plasmid-DNAs (pDNA)) to promote bone repair. The controlled co-delivery approach was achieved from the combination of platelet-derived growth factor-B encoded plasmid-DNA (pPDGF-B) and chitosan-nanoparticle encapsulating pDNA encoded with bone morphogenetic protein-2 (CS-NPs(pBMP2)), which facilitated a burst release of pPDGF-B in 10 days, and a sustained release of pBMP-2 for 5 weeks in vitro. The controlled co-delivery approach was tested for its potential to repair critical-sized rat calvarial defects. The controlled-released pDNAs from the intraoperatively bioprinted bone constructs resulted in ∼40% bone tissue formation and ∼90% bone coverage area at 6 weeks compared to ∼10% new bone tissue and ∼25% total bone coverage area in empty defects. The delivery of growth factors incorporated within the intraoperatively bioprinted constructs could pose as an effective way to enhance bone regeneration in patients with cranial injuries in the future.

Virtual Simulation for Interactive Visualization of 3D Fracture Fixation Biomechanics.

INTRODUCTION: In the surgical fixation of fractures, proper biomechanical stability is key in preventing clinical complications including poor fracture healing, residual deformity, loss of fixation, or implant failure. Stability is largely influenced by treatment decisions made by the surgeon. The interplay of surgeon-controlled variables and their effect on the three-dimensional (3D) biomechanics of a fracture fixation construct are often not intuitive, and current training methods do not facilitate a deep understanding of these interactions. METHODS: A simulation software interface, FracSim, was developed. FracSim is built on a large precomputed library of finite element simulations. The software allows a surgeon to make adjustments to a virtual fracture fixation construct/weight-bearing plan and immediately visualize how these changes affect 3D biomechanics, including implant stress and fracture gap strain, important for clinical success. Twenty-one orthopaedic residents completed an instructor-led educational session with FracSim focused on bridge plating. Subjects completed pretests and posttests of knowledge of biomechanical concepts and a questionnaire. RESULTS: Subjects scored a mean of 5.6/10 on the pretest of biomechanical knowledge. Senior residents scored better than junior residents (P = 0.04). After the educational session with FracSim, residents improved their test scores to a mean of 8.0/10, with a significant improvement (P < 0.001). Questionnaire scores indicated that subjects believed that FracSim had realistic implants, constructs, and motions and that training with FracSim was purposeful, desirable, efficient, fun, and useful for enhancing the understanding of fracture fixation biomechanics. DISCUSSION: This new type of simulation software enables interactive visualization of 3D fracture fixation biomechanics. Limitations of this study include lack of a control group undergoing traditional education and lack of a delayed posttest to assess retention. FracSim may provide an effective and engaging way to promote a deeper understanding of biomechanical concepts in the orthopaedic learner.

Effect of glenoid perforation during total shoulder arthroplasty on glenoid component cement fixation and suprascapular nerve.

BACKGROUND: Arthritic glenoids are susceptible to vault perforation during total shoulder arthroplasty. We investigated the effects of glenoid perforation and subsequent cement extrusion on the suprascapular nerve and on the glenoid cement infiltration. METHODS: Total shoulder arthroplasty using three-pegged glenoid components were performed on 10 cadaveric shoulders assigned to two groups (perforation vs. control). In perforation group, the glenoids were reamed eccentrically and intentionally perforated medially through the central peg hole, whereas control group received perpendicular reaming with no perforation. Bone cement was applied to each peg. Spatial relationship between the extruded cement and the suprascapular nerve, and the amount of cement infiltration into the cancellous bone were evaluated. RESULTS: In perforation group, five specimens were perforated anteriorly, and two posteriorly. In the two posteriorly perforated specimens, the suprascapular nerve was in direct contact with extruded cement at the spinoglenoid notch. Perforation group showed significantly less cement infiltration into the cancellous bone than control group (p = 0.008). CONCLUSIONS: Glenoid perforation decreases the volume of cement infiltration into the cancellous bone potentially compromising glenoid component fixation. Glenoid perforation tends to occur anteriorly rather than posteriorly in arthritic glenoids; however, if perforation occurs posteriorly, the suprascapular nerve is at immediate risk from the extruded cement.Level of evidence: Basic science study.

Effect of Bone Coverage on Acetabular Implant Stresses in Standard and Dual-Mobility Total Hip Arthroplasty Constructs: A Finite Element Model.

Although mechanical stress in total hip arthroplasty modular head-neck junctions is thought to contribute to the risk of trunnionosis and related metal ion disease in total hip arthroplasty, little is known about mechanical stress in the modular acetabular components. Recent retrieval analyses of dual-mobility constructs have demonstrated corrosion between liner and shell in some dual-mobility acetabular components. The objective of this study was to evaluate acetabular stress as a function of acetabular bone coverage, component modularity, and femoral head diameter. A parametric finite element model was created. The acetabulum was set at 40° of abduction and 15° of anteversion; superolateral bone loss up to 50° was modeled; and 28-mm, 32-mm, 36-mm, and 40-mm head sizes were simulated in stance phase of gait. Fixed polyethylene-bearing, monoblock and modular dual-mobility (MDM) acetabular components were evaluated. For traditional fixed-bearing components, the largest peak stress, 49.5 MPa, was observed with 50° of bone loss and a 28-mm head. The lowest peak stress, 6.3 MPa, occurred with complete bone coverage and a 36-mm head. Peak stress in the MDM construct, 25.1 MPa, concentrated in the chromium-cobalt portion of the construct. Larger head diameters are associated with decreased stress in the acetabular component when bone loss is present. An MDM construct with a stiff inner liner may decrease overall stress in the acetabular construct, but focally increased stress near the rim of uncovered acetabular components may increase the risk of metal-on-metal corrosion. [Orthopedics. 2021;44(5):280-284.].

Intra-Operative Bioprinting of Hard, Soft, and Hard/Soft Composite Tissues for Craniomaxillofacial Reconstruction.

Reconstruction of complex craniomaxillofacial (CMF) defects is challenging due to the highly organized layering of multiple tissue types. Such compartmentalization necessitates the precise and effective use of cells and other biologics to recapitulate the native tissue anatomy. In this study, intra-operative bioprinting (IOB) of different CMF tissues, including bone, skin, and composite (hard/soft) tissues, is demonstrated directly on rats in a surgical setting. A novel extrudable osteogenic hard tissue ink is introduced, which induced substantial bone regeneration, with ≈80% bone coverage area of calvarial defects in 6 weeks. Using droplet-based bioprinting, the soft tissue ink accelerated the reconstruction of full-thickness skin defects and facilitated up to 60% wound closure in 6 days. Most importantly, the use of a hybrid IOB approach is unveiled to reconstitute hard/soft composite tissues in a stratified arrangement with controlled spatial bioink deposition conforming the shape of a new composite defect model, which resulted in ≈80% skin wound closure in 10 days and 50% bone coverage area at Week 6. The presented approach will be absolutely unique in the clinical realm of CMF defects and will have a significant impact on translating bioprinting technologies into the clinic in the future.

Additively manufactured patient-specific prosthesis for tumor reconstruction: Design, process, and properties.

Design and processing capabilities of additive manufacturing (AM) to fabricate complex geometries continues to drive the adoption of AM for biomedical applications. In this study, a validated design methodology is presented to evaluate AM as an effective fabrication technique for reconstruction of large bone defects after tumor resection in pediatric oncology patients. Implanting off-the-shelf components in pediatric patients is especially challenging because most standard components are sized and shaped for more common adult cases. While currently reported efforts on AM implants are focused on maxillofacial, hip and knee reconstructions, there have been no reported studies on reconstruction of proximal humerus tumors. A case study of a 9-year-old diagnosed with proximal humerus osteosarcoma was used to develop a patient-specific AM prosthesis for the humerus following tumor resection. Commonly used body-centered cubic (BCC) structures were incorporated at the surgical neck and distal interface in order to increase the effective surface area, promote osseointegration, and reduce the implant weight. A patient-specific prosthesis was fabricated using electron beam melting method from biocompatible Ti-6Al-4V. Both computational and biomechanical tests were performed on the prosthesis to evaluate its biomechanical behavior under varying loading conditions. Morphological analysis of the construct using micro-computed tomography was used to compare the as-designed and as-built prosthesis. It was found that the patient-specific prosthesis could withstand physiologically-relevant loading conditions with minimal permanent deformation (82 µm after 105 cycles) at the medial aspect of the porous surgical neck. These outcomes support potential translation of the patient-specific AM prostheses to reconstruct large bone defects following tumor resection.

Finite Element Analysis of Fracture Fixation.

PURPOSE OF REVIEW: Fracture fixation aims to provide stability and promote healing, but remains challenging in unstable and osteoporotic fractures with increased risk of construct failure and nonunion. The first part of this article reviews the clinical motivation behind finite element analysis of fracture fixation, its strengths and weaknesses, how models are developed and validated, and how outputs are typically interpreted. The second part reviews recent modeling studies of the femur and proximal humerus, areas with particular relevance to fragility fractures. RECENT FINDINGS: There is some consensus in the literature around how certain modeling aspects are pragmatically formulated, including bone and implant geometries, meshing, material properties, interactions, and loads and boundary conditions. Studies most often focus on predicted implant stress, bone strain surrounding screws, or interfragmentary displacements. However, most models are not rigorously validated. With refined modeling methods, improved validation efforts, and large-scale systematic analyses, finite element analysis is poised to advance the understanding of fracture fixation failure, enable optimization of implant designs, and improve surgical guidance.

Nicotine Exposure Via Electronic Cigarettes Significantly Impedes Biomechanical Healing Properties of Tendon Healing in a Rat Model.

PURPOSE: To evaluate the biomechanical and histologic effects on Achilles tendon repair of inhaled combusted tobacco versus nicotine exposure via electronic cigarette versus a control group in a small-animal model (Sprague-Dawley rat). METHODS: Fifty-four Sprague-Dawley rats were randomized into 3 groups: combusted tobacco, e-cigarettes, or control. Experimental rats were exposed to research cigarettes or e-cigarette vapor in a smoking chamber for 4 weeks. Surgical transection and repair of the Achilles tendon were then completed, followed by 2 additional weeks of exposure. Achilles tendons were harvested, and biomechanical tensile testing was performed. Histologic evaluation was completed, including hematoxylin-eosin staining, trichrome staining, and immunohistochemistry analysis for type I and type III collagen. RESULTS: The control group showed the highest mean tensile load to failure, at 41.0 ± 10.4 N (range, 18.3-55.1 N); the cigarette cohort had the second highest mean, at 37.3 ± 11.1 N (range, 14.0-54.7 N); and finally, the vaping group had the lowest mean, at 32.3 ± 8.4 N (range, 17.8-45.1 N). One-way analysis of variance showed a significant difference in load to failure when comparing the control group with the e-cigarette group (P = .026). No statistical difference was detected between the control group and cigarette group (P = .35) or between the e-cigarette group and cigarette group (P = .23). Stiffness and qualitative histologic analysis showed no difference among groups. CONCLUSIONS: This investigation shows that in a rat model, nicotine exposure via e-cigarette significantly impedes the biomechanical healing properties of Achilles tendon surgical repair. CLINICAL RELEVANCE: The results indicate that although e-cigarettes are often used as a perceived "safer" alternative to smoking, their use may have a detrimental effect on tendon load to failure.

Increased Load to Failure in Biceps Tenodesis With All-Suture Suture Anchor Compared With Interference Screw: A Cadaveric Biomechanical Study.

PURPOSE: To compare the biomechanical characteristics of a single radially expanding all-suture anchor with an interference screw for open subpectoral long head of biceps tendon (LHBT) tenodesis. METHODS: Eighteen fresh-frozen matched-pair human cadaveric humeri were used for this biomechanical study. The matched pair humeri were randomly assigned into 2 experimental biceps tenodesis groups: conventional interference screw (CIS) or all-suture suture anchor (ASSA). Open subpectoral LHBT tenodesis was then performed and biomechanical testing was performed using a servohydraulic test frame. A preload of 5 N was applied for 2 minutes before cyclic loading. Displacement was recorded at cycle 300 (D300) and cycle 500 (D500) and at ultimate failure. Data recorded included displacement, load to failure, displacement at failure. Paired t test was used for analysis. RESULTS: Decreased displacement was observed for the CIS group at D300 (1.67 ± 0.57 mm vs 3.35 ± 2.24 mm; P = .04), D500 (2.00 ± 0.76 mm vs 3.87 ± 2.20 mm; P = .04), and at failure (5.17 ± 3.05 mm vs 10.76 ± 2.66 mm; P < .001). Load to failure was lower in CIS specimens (170 ± 24.5 N vs 217.8 ± 51.54 N; P = .02). Failure in each case was tendon pullout for all CIS specimens; in ASSA 6 specimens failed as the suture pulled through the tendon, 2 specimens failed by suture breakage. No difference in stiffness was observed between the 2 groups (CIS = 98.33 ± 22.98 N/m vs ASSA = 75.94 ± 44.83 N/m; P = .20). CONCLUSIONS: Our study found that open subpectoral biceps tenodesis performed with an ASSA construct results in increased load to failure as compared with CIS. However, the CIS did demonstrate decreased displacement as compared to ASSA in this cadaveric biomechanical study. CLINICAL RELEVANCE: ASSA and CIS at time zero provide fixation as indicated by the provider intraoperatively for LHBT tenodesis. ASSA, however, does remove less cortical bone than does CIS and therefore produces a smaller stress riser in the proximal humerus. Further testing as to the integrity of ASSA is warranted to determine the integrity of the tenodesis with cyclical loading.

Biomechanical Comparison of Fibertape Device Repair Techniques of Ligamentous Lisfranc Injury in a Cadaveric Model.

BACKGROUND: Lisfranc ligamentous injuries are complex, and their treatment, along with the preferred method of fixation, is controversial. Implementing a flexible synthetic augmentation device (fibertape) has been described as an alternative to traditional screw fixation. This biomechanical study evaluated two fibertape devices with interference screw fixation: InternalBrace, and InternalBrace with supplementary intercuneiform stabilization. METHODS: The diastasis and relative angular displacement between bones were measured at three midfoot joints in the Lisfranc articulation. Measurements were obtained for the pre-injured, injured, and post-fixation stages under static loading. Specimens then underwent stepwise increases in cyclic loading performed at 1 Hz and 100 cycles, at 100 N ground reaction force intervals from 500 to 1200 N to simulate postoperative loading, and then up to 1800 N to simulate high loads. Failure of fixation was defined as diastasis greater than 2 millimeters at the second-metatarsal - medial-cuneiform joint. RESULTS: InternalBrace specimens demonstrated failures in 3 of 9 (33%) specimens at cyclic loads of 1000 N. Conversely, InternalBrace with Supplementary Limb specimens had 1 failure at 1200 N. The difference in diastasis at the second metatarsal-medial cuneiform joint was statistically significant between the two groups at higher loads of 1600N (p = 0.019) and 1800N (p = 0.029). CONCLUSION: The use of InternalBrace for ligamentous Lisfranc injuries appears to provide a biomechanically viable alternative for withstanding early postoperative protected weight bearing. Furthermore, the use of a supplementary limb in addition to the InternalBrace fibertape fixation method appears to enhance its biomechanical efficacy.