Employing direct electromagnetic coupling to assess acute fracture healing: An ovine model assessment.

OBJECTIVES: This study explored the efficacy of collecting temporal fracture site compliance data via an advanced direct electromagnetic coupling (DEC) system equipped with a Vivaldi-type antenna, novel calibration technique, and multi-antenna setup (termed maDEC) as an approach to monitor acute fracture healing progress in a translational large animal model. The overarching goal of this approach was to provide insights into the acute healing dynamics, offering a promising avenue for optimizing fracture management strategies. METHODS: A sample of twelve sheep, subjected to ostectomies and intramedullary nail fixations, was divided into two groups, simulating normal and impaired healing scenarios. Sequential maDEC compliance or stiffness measurements and radiographs were taken from the surgery until euthanasia at four or eight weeks and were subsequently compared with post-sacrifice biomechanical, micro-CT, and histological findings. RESULTS: The results showed that the maDEC system offered straightforward quantification of fracture site compliance via a multiantenna array. Notably, the rate of change in the maDEC-measured bending stiffness significantly varied between normal and impaired healing groups during both the 4-week (p = 0.04) and 8-week (p = 0.02) periods. In contrast, radiographically derived mRUST healing measurements displayed no significant differences between the groups (p = 0.46). Moreover, the cumulative normalized stiffness maDEC data significantly correlated with post-sacrifice mechanical strength (r2 = 0.80, p < 0.001), micro-CT measurements of bone volume fraction (r2 = 0.60, p = 0.003), and density (r2 = 0.60, p = 0.003), and histomorphometric measurements of new bone area fraction (r2 = 0.61, p = 0.003) and new bone area (r2 = 0.60, p < 0.001). CONCLUSIONS: These data indicate that the enhanced maDEC system provides a non-invasive, accurate method to monitor fracture healing during the acute healing phase, showing distinct stiffness profiles between normal and impaired healing groups and offering critical insights into the healing process's progress and efficiency.

Enhanced bone formation in locally-optimised, low-stiffness additive manufactured titanium implants: An in silico and in vivo tibial advancement study.

A tibial tuberosity advancement (TTA), used to treat lameness in the canine stifle, provides a framework to investigate implant performance within an uneven loading environment due to the dominating patellar tendon. The purpose of this study was to reassess how we design orthopaedic implants in a load-bearing model to investigate potential for improved osseointegration capacity of fully-scaffolded mechanically-matched additive manufactured (AM) implants. While the mechanobiological nature of bone is well known, we have identified a lower limit in the literature where investigation into exceedingly soft scaffolds relative to trabecular bone ceases due to the trade-off in mechanical strength. We developed a finite element model of the sheep stifle to assess the stresses and strains of homogeneous and locally-optimised TTA implant designs. Using additive manufacturing, we printed three different low-stiffness Ti-6Al-4 V TTA implants: 0.8 GPa (Ti1), 0.6 GPa (Ti2) and an optimised design with a 0.3 GPa cortex and 0.1 GPa centre (Ti3), for implantation in a 12-week in vivo ovine pilot study. Static histomorphometry demonstrated uniform bone ingrowth in optimised low-modulus Ti3 samples compared to homogeneous designs (Ti1 and Ti2), and greater bone-implant contact. Mineralising surfaces were apparent in all implants, though mineral apposition rate was only consistent throughout Ti3. The greatest bone formation scores were seen in Ti3, followed by Ti2 and Ti1. Results from our study suggest lower stiffnesses and higher strain ranges improve early bone formation, and that by accounting for loading environments through rational design, implants can be optimised to improve uniform osseointegration. STATEMENT OF SIGNIFICANCE: The effect of different strain ranges on bone healing has been traditionally investigated and characterised through computational models, with much of the literature suggesting higher strain ranges being favourable. However, little has been done to incorporate strain-optimisation into porous orthopaedic implants due to the trade-off in mechanical strength required to induce these microenvironments. In this study, we used finite element analysis to optimise the design of additive manufactured (AM) titanium orthopaedic implants for different strain ranges, using a clinically-relevant surgical model. Our research suggests that there is potential for locally-optimised AM scaffolds in the use of orthopaedic devices to induce higher strains, which in turn encourages de novo bone formation and uniform osseointegration.

Direct electromagnetic coupling to determine diagnostic bone fracture stiffness.

Background: Rapid prediction of adverse bone fracture healing outcome (e.g., nonunion and/or delayed union) is essential to advise adjunct therapies to reduce patient suffering and improving healing outcome. Radiographic diagnostic methods remain ineffective during early healing, resulting in average nonunion diagnosis times surpassing six months. To address this clinical deficit, we developed a novel diagnostic device to predict fracture healing outcome by noninvasive telemetric measurements of fracture bending stiffness. This study evaluated the hypothesis that our diagnostic antenna system is capable of accurately measuring temporal fracture healing stiffness, and advises the utility of this data for expedited prediction of healing outcomes during early (≤3 weeks) fracture recovery. Methods: Fracture repair was simulated, in reverse chronology, by progressively destabilizing cadaveric ovine metatarsals (n=8) stabilized via locking plate fixation. Bending stiffness of each fracture state were predicted using a novel direct electromagnetic coupling diagnostic system, and results were compared to values from material testing (MT) methods. While direct calculation of fracture stiffness in a simplistic cadaver model is possible, comparable analysis of the innumerable permutations of fracture and treatment type is not feasible. Thus, clinical feasibility of direct electromagnetic coupling was explored by parametric finite element (FE) analyses (n=1,632 simulations). Implant mechanics were simulated throughout the course of healing for cases with variations to fracture size, implant type, implant structure, and implant material. Results: For all fracture states, stiffness values predicted by the direct electromagnetic coupling system were not significantly different than those quantified by in vitro MT methods [P=0.587, P=0.985, P=0.975; for comparing intact, destabilized, and fully fractured (FF) states; respectively]. In comparable models, the total implant deflection reduction (from FF to intact states) was less than 10% different between direct electromagnetic coupling measurements (82.2 µm) and FE predictions (74.7 µm). For all treatment parameters, FE analyses predicted nonlinear reduction in bending induced implant midspan deflections for increasing callus stiffness. Conclusions: This technology demonstrates potential as a noninvasive clinical tool to accurately quantify healing fracture stiffness to augment and expedite healing outcome predictions made using radiographic imaging.

Vivaldi Antennas for Contactless Sensing of Implant Deflections and Stiffness for Orthopaedic Applications.

The implementation of novel coaxial dipole antennas has been shown to be a satisfactory diagnostic platform for the prediction of orthopaedic bone fracture healing outcomes. These techniques require mechanical deflection of implanted metallic hardware (i.e., rods and plates), which, when loaded, produce measurable changes in the resonant frequency of the adjacent antenna. Despite promising initial results, the coiled coaxial antenna design is limited by large antenna sizes and nonlinearity in the resonant frequency data. The purpose of this study was to develop two Vivaldi antennas (a.k.a., "standard" and "miniaturized") to address these challenges. Antenna behaviors were first computationally modeled prior to prototype fabrication. In subsequent benchtop tests, metallic plate segments were displaced from the prototype antennas via precision linear actuator while measuring resultant change in resonant frequency. Close agreement was observed between computational and benchtop results, where antennas were highly sensitive to small displacements of the metallic hardware, with sensitivity decreasing nonlinearly with increasing distance. Greater sensitivity was observed for the miniaturized design for both stainless steel and titanium implants. Additionally, these data demonstrated that by taking resonant frequency data during implant displacement and then again during antenna displacement from the same sample, via linear actuators, that "antenna calibration procedures" could be used to enable a clinically relevant quantification of fracture stiffness from the raw resonant frequency data. These improvements mitigate diagnostic challenges associated with nonlinear resonant frequency response seen in previous antenna designs.

Multiscale Contrasts Between the Right and Left Ventricle Biomechanics in Healthy Adult Sheep and Translational Implications.

Cardiac biomechanics play a significant role in the progression of structural heart diseases (SHDs). SHDs alter baseline myocardial biomechanics leading to single or bi-ventricular dysfunction. But therapies for left ventricle (LV) failure patients do not always work well for right ventricle (RV) failure patients. This is partly because the basic knowledge of baseline contrasts between the RV and LV biomechanics remains elusive with limited discrepant findings. The aim of the study was to investigate the multiscale contrasts between LV and RV biomechanics in large animal species. We hypothesize that the adult healthy LV and RV have distinct passive anisotropic biomechanical properties. Ex vivo biaxial tests were performed in fresh sheep hearts. Histology and immunohistochemistry were performed to measure tissue collagen. The experimental data were then fitted to a Fung type model and a structurally informed model, separately. We found that the LV was stiffer in the longitudinal (outflow tract) than circumferential direction, whereas the RV showed the opposite anisotropic behavior. The anisotropic parameter K from the Fung type model accurately captured contrasting anisotropic behaviors in the LV and RV. When comparing the elasticity in the same direction, the LV was stiffer than the RV longitudinally and the RV was stiffer than the LV circumferentially, suggesting different filling patterns of these ventricles during diastole. Results from the structurally informed model suggest potentially stiffer collagen fibers in the LV than RV, demanding further investigation. Finally, type III collagen content was correlated with the low-strain elastic moduli in both ventricles. In summary, our findings provide fundamental biomechanical differences between the chambers. These results provide valuable insights for guiding cardiac tissue engineering and regenerative studies to implement chamber-specific matrix mechanics, which is particularly critical for identifying biomechanical mechanisms of diseases or mechanical regulation of therapeutic responses. In addition, our results serve as a benchmark for image-based inverse modeling technologies to non-invasively estimate myocardial properties in the RV and LV.

A Large Animal Model for Orthopedic Foot and Ankle Research.

Trauma to the soft tissues of the ankle joint distal syndesmosis often leads to syndesmotic instability, resulting in undesired movement of the talus, abnormal pressure distributions, and ultimately arthritis if deterioration progresses without treatment. Historically, syndesmotic injuries have been repaired by placing a screw across the distal syndesmosis to provide rigid fixation to facilitate ligament repair. While rigid syndesmotic screw fixation immobilizes the ligamentous injury between the tibia and fibula to promote healing, the same screws inhibit normal physiologic movement and dorsiflexion. It has been shown that intact screw removal can be beneficial for long-term patient success; however, the exact timing remains an unanswered question that necessitates further investigation, perhaps using animal models. Because of the sparsity of relevant preclinical models, the purpose of this study was to develop a new, more translatable, large animal model that can be used for the investigation of clinical foot and ankle implants. Eight (8) skeletally mature sheep underwent stabilization of the left and right distal carpal bones following transection of the dorsal and interosseous ligaments while the remaining two animals served as un-instrumented controls. Four of the surgically stabilized animals were sacrificed 6 weeks after surgery while the remaining four animals were sacrificed 10 weeks after surgery. Ligamentous healing was evaluated using radiography, histology, histomorphometry, and histopathology. Overall, animals demonstrated a high tolerance to the surgical procedure with minimal complications. Animals sacrificed at 10 weeks post-surgery had a slight trend toward mildly decreased inflammation, decreased necrotic debris, and a slight increase in the healing of the transected ligaments. The overall degree of soft tissue fibrosis/fibrous expansion, including along the dorsal periosteal surfaces/joint capsule of the carpal bones was very similar between both timepoints and often exhibited signs of healing. The findings of this study indicate that the carpometacarpal joint may serve as a viable location for the investigation of human foot and ankle orthopedic devices. Future work may include the investigation of orthopedic foot and ankle medical devices, biologic treatments, and repair techniques in a large animal model capable of providing translational results for human treatment.

Biomechanical, Morphological, and Biochemical Characteristics of Articular Cartilage of the Ovine Humeral Head.

OBJECTIVE: Shoulder pain is commonly attributed to rotator cuff injury or osteoarthritis. Ovine translational models are used to investigate novel treatments aimed at remedying these conditions to prevent articular cartilage degeneration and subsequent joint degradation. However, topographical properties of articular cartilage in the ovine shoulder are undefined. This study investigates the biomechanical, morphological, and biochemical attributes of healthy ovine humeral head articular cartilage and characterizes topographical variations between surface locations. DESIGN: Ten humeral heads were collected from healthy skeletally mature sheep and each was segregated into 4 quadrants using 16 regions of interest (ROIs) across the articular surface. Articular cartilage of each ROI was analyzed for creep indentation, thickness, and sulfated glycosaminoglycan (sGAG) and collagen quantity. Comparisons of each variable were made between quadrants and between ROIs within each quadrant. RESULTS: Percent creep, thickness, and sGAG content, but not collagen content, were significantly different between humeral head quadrants. Subregion analysis of the ROIs within each surface quadrant revealed differences in all measured variables within at least one quadrant. Percent creep was correlated with sGAG (r = -0.32, P = 0.0001). Collagen content was correlated with percent creep (r = 0.32, P = 0.0009), sGAG (r = -0.19, P = 0.049), and thickness (r = -0.19, P = 0.04). CONCLUSIONS: Topographical variations exist in mechanical, morphologic, and biochemical properties across the articular surface of the ovine humeral head. Recognizing this variability in ovine humeral head cartilage will provide researchers and clinicians with accurate information that could impact study outcomes.

Evaluation of lumbar spinal fusion utilizing recombinant human platelet derived growth factor-B chain homodimer (rhPDGF-BB) combined with a bovine collagen/ß-tricalcium phosphate (ß-TCP) matrix in an ovine model.

BACKGROUND CONTEXT: While the clinical effectiveness of recombinant human Platelet Derived Growth Factor-B chain homodimer combined with collagen and ß-tricalcium phosphate (rhPDGF-BB + collagen/ß-TCP) treatment for indications involving hindfoot and ankle is well-established, it is not approved for use in spinal interbody fusion, and the use of autograft remains the gold standard. PURPOSE: The purpose of this study was to compare the effects of rhPDGF-BB + collagen/ß-TCP treatment on lumbar spine interbody fusion in an ovine model to those of autograft bone and collagen/ß-TCP treatments using biomechanical, radiographic, and histological assessment techniques. STUDY DESIGN: Thirty-two skeletally mature Columbian Rambouillet sheep were used to evaluate the safety and effectiveness of rhPDGF-BB + collagen/ß-TCP matrix in a lumbar spinal fusion model. Interbody polyetheretherketone (PEEK) cages contained either autograft, rhPDGF-BB + collagen/ß-TCP, collagen/ß-TCP matrix, or left empty. METHODS: Animals were sacrificed 8- or 16-weeks post-surgery. Spinal fusion was evaluated via post-sacrifice biomechanical, micro-computed tomography (µCT), and histological analysis. Outcomes were statistically compared using a two-way analysis of variance (ANOVA) with an alpha value of 0.05 and a Tukey post-hoc test. RESULTS: There were no statistically significant differences between groups within treatment timepoints for flexion-extension, lateral bending, or axial rotation range of motion, neutral zone, neutral zone stiffness, or elastic zone stiffness. µCT bone volume fraction was significantly greater between treatment groups independent of timepoint where Autograft and rhPDGF-BB + collagen/ß-TCP treatments demonstrated significantly greater bone volume fraction as compared to collagen/ß-TCP (P = .026 and P = .038, respectively) and Empty cage treatments (P = .002 and P = .003, respectively). µCT mean bone density fraction was most improved in rhPDGF-BB + collagen/ß-TCP specimens at the 8 week and 16-week timepoints as compared to all other treatment groups. There were no statistically significant differences in histomorphometric measurements of bone, soft tissue, or empty space between rhPDGF-BB + collagen/ß-TCP and autograft treatments. CONCLUSIONS: The results of this study indicate that the use of rhPDGF-BB combined with collagen/ß-TCP promotes spinal fusion comparable to that of autograft bone. CLINICAL SIGNIFICANCE: The data indicate that rhPDGF-BB combined with collagen/ß-TCP promotes spinal fusion comparably to autograft bone treatment and may offer a viable alternative in large animal spinal fusion. Future prospective clinical studies are necessary to fully understand the role of rhPDGF-BB combined with collagen/ß-TCP in human spinal fusion healing.

Diagnostic prediction of ovine fracture healing outcomes via a novel multi-location direct electromagnetic coupling antenna.

BACKGROUND: Expedient prediction of adverse bone fracture healing (delayed- or non-union) is necessary to advise secondary treatments for improving healing outcome to minimize patient suffering. Radiographic imaging, the current standard diagnostic, remains largely ineffective at predicting nonunions during the early stages of fracture healing resulting in mean nonunion diagnosis times exceeding six months. Thus, there remains a clinical deficit necessitating improved diagnostic techniques. It was hypothesized that adverse fracture healing expresses impaired biological progression at the fracture site, thus resulting in reduced temporal progression of fracture site stiffness which may be quantified prior to the appearance of radiographic indicators of fracture healing (i.e., calcified tissue). METHODS: A novel multi-location direct electromagnetic coupling antenna was developed to diagnose relative changes in the stiffness of fractures treated by metallic orthopaedic hardware. The efficacy of this diagnostic was evaluated during fracture healing simulated by progressive destabilization of cadaveric ovine metatarsals treated by locking plate fixation (n=8). An ovine in vivo comparative fracture study (n=8) was then utilized to better characterize the performance of the developed diagnostic in a clinically translatable setting. In vivo measurements using the developed diagnostic were compared to weekly radiographic images and postmortem biomechanical, histological, and micro computed tomography analyses. RESULTS: For all cadaveric samples, the novel direct electromagnetic coupling antenna displayed significant differences at the fracture site (P<0.05) when measuring a fully fractured sample versus partially intact and fully intact fracture states. In subsequent in vivo fracture models, this technology detected significant differences (P<0.001) in fractures trending towards delayed healing during the first 30 days post-fracture. CONCLUSIONS: This technology, relative to traditional X-ray imaging, exhibits potential to greatly expedite clinical diagnosis of fracture nonunion, thus warranting additional technological development.

Longitudinal tendon healing assessed with multi-modality advanced imaging and tissue analysis.

BACKGROUND: The range of diagnostic modalities available to evaluate superficial digital flexor tendon (SDFT) injury includes magnetic resonance imaging (MRI), computed tomography (CT) and ultrasonography (US). Direct, comprehensive comparison of multi-modality imaging characteristics to end-point data has not previously been performed using a model of tendinopathy but is required to obtain a better understanding of each modality's diagnostic capabilities. OBJECTIVE: To compare CT, MRI and US evaluation to outcome measures for histologic, biochemical and biomechanical parameters using an equine surgical model of tendinopathy. STUDY DESIGN: Controlled experiment. METHODS: Lesions were surgically created in both forelimb SDFTs of eight horses and imaged using MRI, CT and US at seven time points over 12 months. Imaging characteristics were then correlated to end point histologic, biochemical and biomechanical data using lasso regression. Longitudinal lesion size was compared between imaging modalities. RESULTS: Lesion to tendon isoattenuation on CT evaluation correlated with the greatest levels of aggrecan deposition. A significant correlation between cellular density and percentage of tendon involvement on the T2-weighted sequence and signal intensity on the proton density fat saturated (PD FS) sequence was appreciated at the 12-month time point (P = .006, P = .02 respectively). There was no significant correlation between end-point data and US or contrast imaging characteristics. Cross sectional area lesion to tendon measurements were significantly largest on CT evaluation, followed by MRI and then US (P < .001). MAIN LIMITATIONS: Experimentally induced tendon injury with singular end-point data correlation. CONCLUSIONS: Lesion isoattenuation on CT evaluation suggested scar tissue deposition, while T2-weighted hyperintensity indicated hypercellular tendinopathy even in chronic stages of healing. Non contrast-enhanced MRI and CT evaluation correlated most closely to cellular characteristics of surgically damaged tendons assessed over a twelve month study period. Ultrasonographic evaluation underestimates true lesional size and should be interpreted with caution.

Mechanical, biochemical, and morphological topography of ovine knee cartilage.

The knee is the most common site for translational cartilage research in sheep, though topographic features of articular cartilage across surfaces are unspecified. We aimed to characterize the mechanical, morphological, and biochemical properties of articular cartilage across ovine knee surfaces and document variations between and within surface locations. Regions of interest (ROIs) were delineated across surfaces of 10 healthy ovine knees. Articular cartilage at each ROI was measured for creep indentation, thickness, and glycosaminoglycan (GAG) and collagen content. Variables were compared between surface locations (trochlea, and lateral [LFC] and medial [MFC] femoral condyles) and between ROIs within each surface location. Correlations between variables were also assessed. Articular surface location had a significant effect on creep (P < .0001), thickness (P < .0001), and collagen (P = .0007), but not GAG (P = .28). Significant differences in percent creep between ROIs were found within the LFC (P < .0001), MFC (P < .0001), and trochlea (P = .0002). Cartilage thickness was different between ROIs within the LFC, MFC, and trochlea (all P < .0001). The LFC (P = .002) and trochlea (P = .01) each had significant differences in GAG between ROIs. Collagen content between ROIs was different within the LFC (P = .0003), MFC (P = .0005), and trochlea (P < .0001). Collagen content was correlated with thickness (r = -.55), percent creep (r = .47), and GAG (r = -.21). Percent creep was correlated with thickness (r = -.64) and GAG (r = -.19). Topographic variations in mechanical, morphological, and biochemical properties exist across knee cartilage surfaces in sheep. Recognition of this variability is important to optimize study protocols and improve accuracy of results.

Biomechanical comparison of locking compression plate fixation and a novel pedicle screw external fixation to repair equine mandibular fractures.

OBJECTIVE: To determine the biomechanical properties of pedicle screw external fixation (PDW) for equine mandibular fracture repair and compare PDW to locking compression plates (LCP). STUDY DESIGN: Cadaveric study. SAMPLE POPULATION: Sixteen adult equine mandibles. METHODS: Four mandibles were kept intact, while 12 were osteotomized and stabilized with the LCP or PDW construct (6 mandibles/group). Failure, stiffness, and yield were calculated from quasi-static ramp to failure and compared with previous analysis of mandibular fracture constructs. Tooth root involvement and method of failure were determined from radiographs and videos. RESULTS: Locking compression plate constructs achieved greater stiffness and load at failure (4656 ± 577 N-m/radian, 558 ± 27 N-m P < .05) compared with PDW constructs (2626 ± 127 N-m/radian, 315 ± 48 N-m). Yield did not differ between types of fixation (369 ± 57 N-m, 193 ± 35 N-m, P = .145). Tooth involvement was noted in two LCP constructs with failure via bone fracture. Pedicle screw external fixation constructs failed via wire unraveling and screw bending. CONCLUSION: Locking compression plate fixation increased stiffness and failure of constructs but did not influence yield. It also increased the risk to tooth root involvement relative to fixation with PDW. Compared with another study, PDW offered stiffness and failure similar to an intraoral splint with interdental wires, external fixator (EF), and external fixator with wires (EFW) and yield similar to an EF, an EFW, and a dynamic compression plate. CLINICAL RELEVANCE: Pedicle screw external fixation offers biomechanical stability comparable to other relevant mandibular fixation techniques and reduces the risk of tooth root damage compared with LCP fixation.

Biomechanical and Histological Assessment of a Polyethylene Terephthalate Screw Retention Technology in an Ovine Metatarsal Fracture Model.

OBJECTIVE: Screw loosening in fracture fixation poses a clinical risk which may lead to implant failure, particularly in poor bone quality. The objective of this study was to examine the effectiveness of a novel screw retention technology (SRT) for increased screw purchase in a large animal metatarsal fracture model. STUDY DESIGN: This was a biomechanical, radiographic, and histological study utilizing an ovine metatarsal fracture model. Twenty-four sheep metatarsi underwent 3-mm ostectomies and were repaired with a nine-hole plate and 3.5-mm screws placed in oversized 3.5-mm holes to simulate worst case revision surgeries (i.e. no initial screw thread bone contact). Sheep were sacrificed at 3, 6 or 12 weeks (n = 6 each) post-operation. Post-sacrifice, each surgically implanted screw underwent either destructive mechanical testing or histomorphometric analyses. RESULTS: Treated metatarsi showed improved screw retention and normal fracture healing. Significant improvement in breakout strength and pullout strength of screws treated with the SRT were found as a function of healing time. Histologically, bone ingrowth at the screw interface was also shown to significantly increase with healing time. Improvements in fracture healing, indicated by an increase in bone fraction and decrease in void space at the osteotomy, were also observed with healing time. CONCLUSION: The results demonstrate the effectiveness of the SRT as a method for improved screw retention in a rescue-screw type scenario.

Ex vivo comparison of intradermal closures with conventional monofilament suture vs unidirectional barbed suture in dogs.

OBJECTIVE: To evaluate the mechanical properties, strength, and quality of seal provided by continuous intradermal suture lines closed with barbed suture vs monofilament suture. STUDY DESIGN: Experimental study. SAMPLE POPULATION: Forty-eight full-thickness wounds in canine cadavers. METHODS: Four-centimeter-long parasagittal cutaneous wounds were created in canine cadavers. Each intradermal closure was closed with smooth monofilament suture and terminated with a 2 + 1 Aberdeen knot (n = 24) or a unidirectional barbed suture terminated with a single end pass (n = 24). Wounds (n = 12/group) were harvested, and a servohydraulic machine applied tensile load perpendicular to the long axis of the suture line. A load-displacement curve was generated; maximum load, displacement, stiffness, and mode of construct failure were recorded. Harvested wounds were placed in a watertight construct to measure the volume of fluid leaking over 3 minutes at 1.0 ± 0.1 psi. RESULTS: Stiffness did not differ between constructs (P > .05). Incisions closed with monofilament sutures sustained higher maximum load (311.21 N ± 87.40) and displacement at failure (21.19 mm ± 4.51) compared with those with barbed sutures (116.38 N ± 42.82 and 15.03 mm ± 2.32, respectively, P < .05). Closures with monofilament sutures leaked more (4.38 mL ± 7.90) compared with those with barbed sutures (0.15 mL ± 0.43, P < .05). CONCLUSION: Monofilament sutures resulted in stronger constructs, whereas barbed suture constructs provided a better watertight seal. CLINICAL SIGNIFICANCE: While unidirectional barbed sutures may improve watertight skin closure, surgeons should consider using conventional monofilament sutures when mechanical strength of the closure is of primary concern.

Utilizing Multiple BioMEMS Sensors to Monitor Orthopaedic Strain and Predict Bone Fracture Healing.

Current diagnostic modalities, such as radiographs or computed tomography, exhibit limited ability to predict the outcome of bone fracture healing. Failed fracture healing after orthopaedic surgical treatments are typically treated by secondary surgery; however, the negative correlation of time between primary and secondary surgeries with resultant health outcome and medical cost accumulation drives the need for improved diagnostic tools. This study describes the simultaneous use of multiple (n = 5) implantable flexible substrate wireless microelectromechanical (fsBioMEMS) sensors adhered to an intramedullary nail (IMN) to quantify the biomechanical environment along the length of fracture fixation hardware during simulated healing in ex vivo ovine tibiae. This study further describes the development of an antenna array for interrogation of five fsBioMEMS sensors simultaneously, and quantifies the ability of these sensors to transmit signal through overlaying soft tissues. The ex vivo data indicated significant differences associated with sensor location on the IMN (p < 0.01) and fracture state (p < 0.01). These data indicate that the fsBioMEMS sensor can serve as a tool to diagnose the current state of fracture healing, and further supports the use of the fsBioMEMS as a means to predict fracture healing due to the known existence of latency between changes in fracture site material properties and radiographic changes. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1873-1880, 2019.

Comparison of in vivo remodeling of urinary bladder matrix and acellular dermal matrix in an ovine model.

AIM: Biologically derived surgical graft materials come from a variety of sources with varying mechanical properties. This study aimed to evaluate the host response and mechanical performance of two extracellular matrix devices in a large animal preclinical model. MATERIALS & METHODS: Bilateral defects were created in the fascia lata of sheep and repaired with either an acellular dermal matrix (ADM) or urinary bladder matrix (UBM). After 1 or 3 months, the repair site was explanted for histological and mechanical analysis. RESULTS & CONCLUSION: Despite pre-implantation mechanical differences, both UBM and ADM demonstrated similar mechanical performance at 3 months. However, UBM was completely remodeled into site-appropriate tissue by 3 months, while ADM showed limited tissue incorporation.

Biomechanical and histologic assessment of a novel screw retention technology in an ovine lumbar fusion model.

BACKGROUND CONTEXT: Screw loosening is a prevalent failure mode in orthopedic hardware, particularly in osteoporotic bone or revision procedures where the screw-bone engagement is limited. PURPOSE: The objective of this study was to evaluate the efficacy of a novel screw retention technology (SRT) in an ovine lumbar fusion model. STUDY DESIGN/SETTING: This was a biomechanical, radiographic, and histologic study utilizing an ovine lumbar spine model. METHODS: In total, 54 (n=54) sheep lumbar spines (L2-L3) underwent posterior lumbar fusion (PLF) via pedicle screw fixation, connecting rod, and bone graft. Following three experimental variants were investigated: positive control (ideal clinical scenario), negative control (simulation of compromised screw holes), and SRT treatments. Biomechanical and histologic analyses of the functional spinal unit (FSU) were determined as a function of healing time (0, 3, and 12 months postoperative). RESULTS: Screw pull-out, screw break-out, and FSU stability of the SRT treatments were generally equivalent to the positive control group and considerably better than the negative control group. Histomorphology of the SRT treatment screw region of interest (ROI) observed an increase in bone percentage and decrease in void space during healing, consistent with ingrowth at the implant interface. The PLF ROI observed similar bone percentage throughout healing between the SRT treatment and positive control. Less bone formation was observed for the negative control. CONCLUSIONS: The results of this study demonstrate that the SRT improved screw retention and afforded effective FSU stabilization to achieve solid fusion in an otherwise compromised fixation scenario in a large animal model.

Bony ingrowth potential of 3D-printed porous titanium alloy: a direct comparison of interbody cage materials in an in vivo ovine lumbar fusion model.

BACKGROUND CONTEXT: There is significant variability in the materials commonly used for interbody cages in spine surgery. It is theorized that three-dimensional (3D)-printed interbody cages using porous titanium material can provide more consistent bone ingrowth and biological fixation. PURPOSE: The purpose of this study was to provide an evidence-based approach to decision-making regarding interbody materials for spinal fusion. STUDY DESIGN: A comparative animal study was performed. METHODS: A skeletally mature ovine lumbar fusion model was used for this study. Interbody fusions were performed at L2-L3 and L4-L5 in 27 mature sheep using three different interbody cages (ie, polyetheretherketone [PEEK], plasma sprayed porous titanium-coated PEEK [PSP], and 3D-printed porous titanium alloy cage [PTA]). Non-destructive kinematic testing was performed in the three primary directions of motion. The specimens were then analyzed using micro-computed tomography (µ-CT); quantitative measures of the bony fusion were performed. Histomorphometric analyses were also performed in the sagittal plane through the interbody device. Outcome parameters were compared between cage designs and time points. RESULTS: Flexion-extension range of motion (ROM) was statistically reduced for the PTA group compared with the PEEK cages at 16 weeks (p-value=.02). Only the PTA cages demonstrated a statistically significant decrease in ROM and increase in stiffness across all three loading directions between the 8-week and 16-week sacrifice time points (p-value≤.01). Micro-CT data demonstrated significantly greater total bone volume within the graft window for the PTA cages at both 8 weeks and 16 weeks compared with the PEEK cages (p-value<.01). CONCLUSIONS: A direct comparison of interbody implants demonstrates significant and measurable differences in biomechanical, µ-CT, and histologic performance in an ovine model. The 3D-printed porous titanium interbody cage resulted in statistically significant reductions in ROM, increases in the bone ingrowth profile, as well as average construct stiffness compared with PEEK and PSP.

Use of pressure mapping for quantitative analysis of pressure points induced by external coaptation of the distal portion of the pelvic limb of dogs.

OBJECTIVE To quantitatively measure the amount of pressure induced at the calcaneus and cranial tibial surface of dogs by use of 2 cast configurations. ANIMALS 13 client- or student-owned dogs. PROCEDURES Pressure sensors were placed over the calcaneus and cranial tibial surface. Dogs then were fitted with a fiberglass cast on a pelvic limb extending from the digits to the stifle joint (tall cast). Pressure induced over the calcaneus and proximal edge of the cast at the level of the cranial tibial surface was simultaneously recorded during ambulation. Subsequently, the cast was shortened to end immediately proximal to the calcaneus (short cast), and data acquisition was repeated. Pressure at the level of the calcaneus and cranial tibial surface for both cast configurations was compared by use of paired t tests. RESULTS The short cast created significantly greater peak pressure at the level of the calcaneus (mean ± SD, 0.2 ± 0.07 MPa), compared with peak pressure created by the tall cast (0.1 ± 0.06 MPa). Mean pressure at the proximal cranial edge of the cast was significantly greater for the short cast (0.2 ± 0.06 MPa) than for the tall cast (0.04 ± 0.03 MPa). CONCLUSIONS AND CLINICAL RELEVANCE A cast extended to the level of the proximal portion of the tibia caused less pressure at the level of the calcaneus and the proximal cranial edge of the cast. Reducing the amount of pressure at these locations may minimize the potential for pressure sores and other soft tissue injuries.

An investigation of shock wave therapy and low-intensity pulsed ultrasound on fracture healing under reduced loading conditions in an ovine model.

The use of shock wave therapy (SWT) and low-intensity pulsed ultrasound (LIPUS) as countermeasures to the inhibited fracture healing experienced during mechanical unloading was investigated by administering treatment to the fracture sites of mature, female, Rambouillet Columbian ewes exposed to partial mechanical unloading or full gravitational loading. The amount of fracture healing experienced by the treatment groups was compared to controls in which identical surgical and testing protocols were administered except for SWT or LIPUS treatment. All groups were euthanized after a 28-day healing period. In vivo mechanical measurements demonstrated no significant alteration in fixation plate strains between treatments within either partial unloading group. Similarly, DXA BMD and 4-point bending stiffness were not significantly altered following either treatment. µCT analyses demonstrated lower callus bone volume for treated animals (SWT and LIPUS, p < 0.01) in the full gravity group but not between reduced loading groups. Callus osteoblast numbers as well as mineralized surface and bone formation rate were significantly elevated to the level of the full gravity groups in the reduced loading groups following both SWT and LIPUS. Although no increase in 4-week mechanical strength was observed, it is possible that an increase in the overall rate of fracture healing (i.e., callus strength) may be experienced at longer time points under partial loading conditions given the increase in osteoblast numbers and bone formation parameters following SWT and LIPUS. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:921-929, 2018.