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.

Establishment of a Neurodegenerative Charcot Mouse Model.

BACKGROUND: This study aimed to mimic the changes from Charcot neuropathic arthropathy in humans by examining the effects of exposing diet-induced obese (DIO) mice to neurotrauma through a regimented running protocol. METHODS: Forty-eight male wild-type C57BL/6J mice were obtained at age 6 weeks and separated into 2 groups for diet assignment. After a 1-week acclimation period, half of the mice consumed a high-fat diet (60% fat by kcal) ad libitum to facilitate neuropathic diet-induced obesity whereas the other half were control mice and consumed an age-matched standard low-fat control diet (10% fat by kcal). At age 12 weeks, half of the animals from each group were subjected to a high-intensity inclined treadmill running protocol, which has been previously demonstrated to induce neurotrauma. Sensory testing and radiographic analyses were periodically performed. Histopathologic analyses were performed post killing. RESULTS: DIO mice had significantly higher bodyweights, higher body fat percentages, and lower bone mineral density than wildtype control mice that were fed a normal diet throughout the experiment (P < .001 for each). DIO mice displayed significantly reduced sensory function in week 1 (P = .005) and this worsened over time, requiring 20.6% more force for paw withdrawal by week 10 (P < .001). DIO mice that ran demonstrated greater midfoot subluxation and tarsal instability over all time points compared with normal-diet mice that ran (P < .001). Histopathologic analyses revealed that DIO mice that ran demonstrated significant changes compared with controls that ran (P < .001 for each parameter). CONCLUSION: Changes akin to the earliest changes observed in or before joint destruction identified in diabetic Charcot neuropathic arthropathy in humans were observed. CLINICAL RELEVANCE: There is currently no standard of treatment for patients with Charcot neuropathic arthropathy. This study establishes a protocol for an animal model that can be used to study and compare interventions to treat this disease.

Extrusion and characterization of recycled polyethylene terephthalate (rPET) filaments compounded with chain extender and impact modifiers for material-extrusion additive manufacturing.

The continuous growth of annual production and consumption of polyethylene terephthalate (PET) is coined with increasing waste that leaks into the environment, landfills and oceans as microplastics and nano plastics fragments. Upcycling the recycled PET to make a feedstock for the fast-growing material-extrusion additive manufacturing (MEX-AM) technology can contribute to the solution and supports the concept of sustainable materials. In this work, extrudable filaments comprising recycled polyethylene terephthalate (rPET) with low-cost additives, such as pyromellitic dianhydride (PMDA) as a chain extender, styrene-ethylene-butylene-styrene terpolymer functionalized with maleic anhydride (SEBS-g-MA), a thermal modifier and toughening agent, ethylene-ethyl acrylate-glycidyl methacrylate terpolymer (E-EA-GMA), a functional reactive elastomeric impact modifier and ethylene-ethyl-acrylate (EEA), a non-reactive elastomeric impact modifier, have been fabricated using the twin-screw extruder. The optimum extrusion process parameters for producing uniform filaments of different rPET compounded formulations have been identified, this includes the extrusion die temperature of 280 °C and the screw speed of 150 ± 3 rpm. The compounded filaments are then printed into standard ASTM test specimens for thermal characterization and mechanical characterization, including glass transition and melting temperatures, crystallinity and crystallization temperature, tensile strength, tensile modulus, ductility, flexural strength, and Izod impact energy. Furthermore, the melt flow index for the filaments was measured. More significantly, the experimental data showed that compounding rPET with such additives in the reactive twin-screw extrusion process results in uniform filaments that display advantageous thermal and mechanical properties and can be used as a feedstock in the MEX-AM technology. This study suggests that compounding the recycled PET pellets with low-cost additives while extruding them into filaments for MEX-AM offers excellent potential to make high-value-added customized products from a sustainable polymer feedstock, such as prototyping, tooling, testing components or end-use internal components for small machines and cars.

Ulnohumeral joint static cartilage compression is affected by radial head implant size.

INTRODUCTION: Radiocapitellar joint arthroplasty is a commonly performed procedure, which often leads to early failure or instability. Few studies assess the effect of radiocapitellar joint arthroplasty on the ulnohumeral joint. We hypothesized that static forces of contact (compressing cartilage, or cartilage relaxation contact force) would reveal the effect of varying radial head implant size and elbow position on the ulnohumeral joint. METHODS: A minimally-invasive method of measuring cartilage relaxation contact force was utilized in 10 fresh-frozen human cadaveric specimens that did not require significant dissection or intraarticular sensor placement. Specimens were rigidly fixed in various positions of elbow flexion and forearm pronosupination with increasing radial head implant lengths. Uniaxial distracting forces were applied and displacement was repeatedly measured with resultant best-fit polynomial curves to determine inflections corresponding to the force required to overcome static cartilage relaxation as in previous work. FINDINGS: Baseline mean (intra-cadaver) cartilage relaxation contact force was 11.8 N (standard error of the mean = 0.3) at 90° of elbow flexion and neutral rotation. There was little variation within specimens (Intraclass correlation coefficient > 0.94). Cartilage relaxation contact force increased at the ulnohumeral joint with radial head implant overstuffing (> 4 mm, P < 0.05) and elbow flexion (120°, P < 0.001). Pronosupination altered cartilage relaxation contact force in an implant-length independent manner (P < 0.05). INTERPRETATION: Radiocapitellar joint arthroplasty implant length and elbow joint position independently contribute to increased cartilage relaxation contact force at the ulnohumeral joint. This further supports attempts at anatomic reconstruction of the radiocapitellar joint to prevent pathologic ulnohumeral joint loading.

Erythropoietin-PLGA-PEG as a local treatment to promote functional recovery and neurovascular regeneration after peripheral nerve injury.

BACKGROUND: Traumatic peripheral nerve injury (TPNI) is a major medical problem with no universally accepted pharmacologic treatment. We hypothesized that encapsulation of pro-angiogenic erythropoietin (EPO) in amphiphilic PLGA-PEG block copolymers could serve as a local controlled-release drug delivery system to enhance neurovascular regeneration after nerve injury. METHODS: In this study, we synthesized an EPO-PLGA-PEG block copolymer formulation. We characterized its physiochemical and release properties and examined its effects on functional recovery, neural regeneration, and blood vessel formation after sciatic nerve crush injury in mice. RESULTS: EPO-PLGA-PEG underwent solution-to-gel transition within the physiologically relevant temperature window and released stable EPO for up to 18 days. EPO-PLGA-PEG significantly enhanced sciatic function index (SFI), grip strength, and withdrawal reflex post-sciatic nerve crush injury. Furthermore, EPO-PLGA-PEG significantly increased blood vessel density, number of junctions, and myelinated nerve fibers after injury. CONCLUSION: This study provides promising preclinical evidence for using EPO-PLGA-PEG as a local controlled-release treatment to enhance functional outcomes and neurovascular regeneration in TPNI.

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.

Cost-Effective Modeling of Thromboembolic Chemoprophylaxis for Total Ankle Arthroplasty.

BACKGROUND: Symptomatic venous thromboembolism (VTE) following total ankle arthroplasty (TAA) can cause substantial morbidity and mortality. To prevent this complication, surgeons often prescribe postoperative chemoprophylaxis. However, much controversy exists regarding the efficacy of chemoprophylaxis because of the limited studies exploring its use. Furthermore, even less is known about its cost-effectiveness. Therefore, this study sought to determine the cost-effectiveness of commonly prescribed chemoprophylactic agents using a break-even analysis economic model. METHODS: The literature was searched, and an online database was used to identify patients who developed a symptomatic VTE after undergoing TAA. Our institutional records were used to estimate the cost of treating a symptomatic VTE, and an online drug database was used to obtain the cost of commonly prescribed chemoprophylactic agents. A break-even analysis was then performed to determine the final break-even rate necessary to make a drug cost-effective. RESULTS: The low and high rates of symptomatic VTE were determined to be 0.46% and 9.8%. From 2011 to 2021, a total of 3455 patients underwent total ankle arthroplasty. Of these patients, 16 developed a postoperative symptomatic VTE (1.01%). Aspirin 81 mg was cost-effective if the initial symptomatic VTE rates decreased by an absolute risk reduction (ARR) of 0.0003% (NNT = 31 357). Aspirin 325 mg was also cost-effective if the initial rates decreased by an ARR 0.02% (NNT = 5807). Likewise, warfarin (5 mg) was cost-effective at all initial rates with an ARR of 0.02% (NNT = 4480). In contrast, enoxaparin (40 mg) and rivaroxaban (20 mg) were only cost-effective at higher initial symptomatic VTE rates with ARRs of 1.48% (NNT = 68) and 5.36% (NNT = 19). Additional analyses demonstrated that enoxaparin (40 mg) and rivaroxaban (20 mg) become cost-effective when costs of treating a symptomatic VTE are higher than our estimates. CONCLUSION: Chemoprophylaxis following TAA can be cost-effective. A tailored approach to VTE prophylaxis with cost-effectiveness in mind may be beneficial to the patient and health system.

Achilles Tendon Ruptures and Repair in Athletes-a Review of Sports-Related Achilles Injuries and Return to Play.

PURPOSE OF REVIEW: Achilles tendon ruptures (ATR) are detrimental to sports performance, and optimal treatment strategy and guidelines on return to play (RTP) remain controversial. This current review investigates the recent literature surrounding nonoperative versus operative management of ATR, clinical outcomes, and operative techniques to allow the athlete a successful return to their respective sport. RECENT FINDINGS: The Achilles tendon (AT) is crucial to the athlete, as it is essential for explosive activities such as running and jumping. Athletes that sustain an ATR play in fewer games and perform at a lower level of play compared to age-matched controls. Recent studies also theorize that ATRs occur due to elongation of the tendon with fatigue failure. Biomechanical studies have focused on comparing modes of fixation under dynamic loading to recreate this mechanism. ATRs can be career-ending injuries. Fortunately, the recent incorporation of early weight-bearing and functional rehabilitation programming for non-operative and operative patients alike proves to be beneficial. Especially for those treated nonoperatively, with the incorporation of functional rehabilitation, the risk of re-rupture among non-operative patients is beginning to approach the historical lower risk of re-rupture observed among patients treated operatively. Despite this progress in decreasing risk of re-rupture particularly among non-operative patients, operative managements are associated with unique benefits that may be of particular interest for athletes and active individuals. Recent studies demonstrate that operative intervention improves strength and functional outcomes with more efficacy compared to nonoperative management with rehabilitation. The current literature supports operative intervention in elite athletes to improve performance and shorten the duration to RTP. However, we acknowledge that surgical intervention does have inherent risks. Ultimately, most if not all young and/or high-level athletes with an ATR benefit from surgical repair, but it is crucial to take a stepwise algorithmic approach and consider other factors, which may lead towards nonoperative intervention. These factors include age, chronicity of injury, gap of ATR, social factors, and medical history amongst others in this review.

Animal model detects early pathologic changes of Charcot neuropathic arthropathy.

Charcot neuropathic arthropathy is a degenerative, debilitating disease that affects the foot and ankle in patients with diabetes and peripheral neuropathy, often resulting in destruction, amputation. Proposed etiologies include neurotraumatic, inflammatory, and neurovascular. There has been no previous animal model for Charcot. This study proposes a novel rodent model of induced neuropathic arthropathy to understand the earliest progressive pathologic changes of human Charcot. High-fat-diet-induced obese (DIO) Wild-type C57BL/6J mice (n = 8, diabetic) and age-matched low-fat-diet controls (n = 6) were run on an inclined high-intensity treadmill protocol four times per week for 7 weeks to induce mechanical neurotrauma to the hind-paw, creating Charcot neuropathic arthropathy. Sensory function and radiologic correlation were assessed; animals were sacrificed to evaluate hindpaw soft tissue and joint pathology. With this model, Charcot-DIO mice reveals early pathologic features of Charcot neuropathic arthropathy, a distinctive subchondral microfracture callus, perichondral/subchondral osseous hypertrophy/osteosclerosis, that precedes fragmentation/destruction observed in human surgical pathology specimens. There is intraneural vacuolar-myxoid change and arteriolosclerosis. The DIO mice demonstrated significant hot plate sensory neuropathy compared (P < 0.01), radiographic collapse of the longitudinal arch in DIO mice (P < 0.001), and diminished bone density in DIO, compared with normal controls. Despite exercise, high-fat-DIO mice increased body weight and percentage of body fat (P < 0.001). This murine model of diet-induced obesity and peripheral neuropathy, combined with repetitive mechanical trauma, simulates the earliest changes observed in human Charcot neuropathic arthropathy, of vasculopathic-neuropathic etiology. An understanding of early pathophysiology may assist early diagnosis and intervention and reduce patient morbidity and mortality in Charcot neuropathic arthropathy.

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.