How metal augments, polyethylene thickness and stem length affect tibial baseplate load transfer in revision total knee arthroplasty.

BACKGROUND: It is unclear howmetal augments,polyethylene (PE) liner thickness, and length of cemented stemcontribute to load transferwhen reconstructing uncontained tibial metaphyseal bone loss of Anderson Orthopedic Research Institute (AORI) Type II defects during revision total knee arthroplasty (rTKA).The aimof this study is to understand the impact of these three variableson load transfer through the tibial baseplate. For a fixed defect depth, we hypothesized that there is a particular combination of liner and augment thickness and stem length that minimizes bone stress, reducing the risk of aseptic loosening. METHODS: We conducted a finite element analysis (FEA) to model stresses at the bone-cement interface with different iterations of metal augments, PE liner thicknesses andfully-cemented stems lengths. RESULTS: For a 20 mm tibial defect, constructs with thicker metal augments and thinner polyethylene liners were superior. Constructswith a fully cemented stem further reduced bone stress on the tibial plateau. Bone stress was lowest when a 100 mm fully-cemented stem was used, while stems between 30 mm - 80 mm produced similar results. CONCLUSIONS: When addressing a tibial bone defect of AORI Type II in rTKA, our FEA model demonstrates that surgeons should opt to use the thickest metal augments in combination with afully-cemented stem with an added length of at least 30 mm, which allows for surgical flexibility together with the most stable construct.Our study is notably limited by lack of modeling of knee joint moments, which are important when considering micromotion, bone-implant interface and stem effectiveness.

An analytical model of lateral condylar plate working length.

BACKGROUND: The locking plate is a common device to treat distal femur fractures. Healing is affected by construct stiffness, thus many surgeon-controlled variables such as working length have been examined for their effects on strain at the fracture. No convenient analytical model which aids surgeons in determining working length has yet been described. We propose an analytical model and compare it to finite element analysis and cadaveric biomechanical testing. METHODS: First, an analytical model based on a cantilever beam equation was derived. Next, a finite element model was developed based on a CT scan of a "fresh-frozen" cadaveric femur. Third, biomechanical testing in single-leg stance loading was performed on the cadaver. In all methods, strain at the fracture was recorded. An ANCOVA test was conducted to compare the strains. FINDINGS: In all models, as the working length increased so did strain. For strain at the fracture, the shortest working length (35 mm) had a strain of 8% in the analytical model, 9% in the finite element model, and 7% for the cadaver. The longest working length (140 mm) demonstrated strain of 15% in the analytical model, and the finite element and biomechanical tests both demonstrated strain of 14%. INTERPRETATION: The strain predicted by the analytical model was consistent with the strain observed in both the finite element and biomechanical models. As demonstrated in existing literature, increasing the working length increases strain at the fracture site. Additional work is required to refine and establish validity and reliability of the analytical model.

Finite Element Evaluation of the Femoral Neck System as Prophylactic Fixation to Prevent Contralateral Hip Fractures.

Introduction: Hip fractures cause significant morbidity and mortality for geriatric patients, and incidence is increasing as the population ages. Following a primary hip fracture, up to 20% may suffer a contralateral hip fracture within 5 years despite fracture risk reduction measures, including fall prevention and osteoporosis pharmacologic treatment. The aim of this study is to assess whether insertion of the Femoral Neck System (Depuy Synthes, West Chester, PA) into the contralateral proximal femur may strengthen the bone and decrease the incidence of contralateral hip fractures. Materials and Methods: ScanIP, an image processing software was used to produce 3-dimensional models of a cadaver femur with the implanted device. Models were meshed and exported to Abaqus for finite element analysis to evaluate the device's ability to reduce stress in the proximal femur. Results were analyzed for element-wise volume and von-Mises stresses. Results: The implant reduced peak stress and bone failure at all levels of bone quality. Specifically in osteoporotic bone, the implant decreased peak stress by 27%, proximal femur trabecular bone failure by 5% and cortical bone failure by 100% in the femoral neck. Conclusions: Our results from computer generated finite element analyses indicate that the Femoral Neck System may strengthen an osteoporotic proximal femur in the event of a lateral fall. Further investigation with expanded finite element analysis and cadaveric biomechanical studies are needed to validate these results.

Hospital-wide cardiac arrest in situ simulation to identify and mitigate latent safety threats.

BACKGROUND: Cardiac arrest resuscitation requires well-executed teamwork to produce optimal outcomes. Frequency of cardiac arrest events differs by hospital location, which presents unique challenges in care due to variations in responding team composition and comfort levels and familiarity with obtaining and utilizing arrest equipment. The objective of this initiative is to utilize unannounced, in situ, cardiac arrest simulations hospital wide to educate, evaluate, and maximize cardiac arrest teams outside the traditional simulation lab by systematically assessing and capturing areas of opportunity for improvement, latent safety threats (LSTs), and key challenges by hospital location. METHODS: Unannounced in situ simulations were performed at a city hospital with multidisciplinary cardiac arrest teams responding to a presumed real cardiac arrest. Participants and facilitators identified LSTs during standardized postsimulation debriefings that were classified into equipment, medication, resource/system, or technical skill categories. A hazard matrix was used by multiplying occurrence frequency of LST in simulation and real clinical events (based on expert opinion) and severity of the LST based on agreement between two evaluators. RESULTS: Seventy-four in situ cardiac arrest simulations were conducted hospital wide. Hundreds of safety threats were identified, analyzed, and categorized yielding 106 unique latent safety threats: 21 in the equipment category, 8 in the medication category, 41 in the resource/system category, and 36 in the technical skill category. The team worked to mitigate all LSTs with priority mitigation to imminent risk level threats, then high risk threats, followed by non-imminent risk LSTs. Four LSTs were deemed imminent, requiring immediate remediation post debriefing. Fifteen LSTs had a hazard ratio greater than 8 which were deemed high risk for remediation. Depending on the category of threat, a combination of mitigating steps including the immediate fixing of an identified problem, leadership escalation, and programmatic intervention recommendations occurred resulting in mitigation of all identified threats. CONCLUSIONS: Hospital-wide in situ cardiac arrest team simulation offers an effective way to both identify and mitigate LSTs. Safety during cardiac arrest care is improved through the use of a system in which LSTs are escalated urgently, mitigated, and conveyed back to participants to provide closed loop debriefing. Lastly, this hospital-wide, multidisciplinary initiative additionally served as an educational needs assessment allowing for informed, iterative education and systems improvement initiatives targeted to areas of LSTs and areas of opportunity.

Difficult Delivery and Neonatal Resuscitation: A Novel Simulation for Emergency Medicine Residents.

INTRODUCTION: Newborn delivery and resuscitation are rare, but essential, emergency medicine (EM) skills. We evaluated the effect of simulation on EM residents' knowledge, confidence, and clinical skills in managing shoulder dystocia and neonatal resuscitation. METHODS: We developed a novel simulation that integrates a shoulder dystocia with neonatal resuscitation and studied a convenience sample of EM residents. Each 15-minute simulation was run with one learner, a simulated nurse, and a standardized patient in situ in the emergency department. The learner was required to reduce a shoulder dystocia and then perform neonatal resuscitation. We debriefed with plus/delta format, standardized teaching points, and individualized feedback. We assessed knowledge with a nine-question multiple choice test, confidence with five-point Likert scales, and clinical performance using a checklist of critical actions. Residents repeated all measures one year after the simulation. RESULTS: A total of 23 residents completed all measures. At one-year post-intervention, residents scored 15% higher on the knowledge test. All residents increased confidence in managing shoulder dystocia on a five-point Likert scale (1.4 vs 2.8) and 80% increased confidence in performing neonatal resuscitation (1.8 vs 3.0). Mean scores on the checklist of critical actions improved by 19% for shoulder dystocia and by 27% for neonatal resuscitation. CONCLUSION: Implementing simulation may improve EM residents' knowledge, confidence, and clinical skills in managing shoulder dystocia and neonatal resuscitation.

A Simulated Mass Casualty Incident Triage Exercise: SimWars.

Introduction: This multipatient simulation exercise encompasses triage by hospital medical providers during a mass casualty incident (MCI) involving gas line explosion with building collapse. The SimWars format allows two teams to participate in identical simulations coupled with active audience observation, followed by facilitated group discussion. The exercise requires real-time knowledge application of MCI management and helps learners develop a framework for rapidly classifying and dispositioning MCI patients. Methods: Two teams of provider pairs completed MCI triage of 12 simulated patients in 8 minutes with an objective of quickly and accurately dispositioning within hospital bed availability. Participants included emergency medicine and surgery physicians, with active observation by mixed provider audiences. Observers completed a checklist per patient (category: urgent/emergent/not emergent, disposition: bed type/location). At simulation conclusion, a 45-minute facilitated discussion compared observers' self-assessment of MCI patient management with the simulation teams' decisions. Finally, an expert panel discussed management decisions and MCI triage pearls. Results: Team performances (N = 4) and audience responses (N = 164) were similar on seven of 12 patients, allowing robust discussion. Participants completed an evaluation at exercise conclusion; 37% reported good/excellent ability to accomplish MCI initial triage and disposition before this exercise compared to 100% after, a statistically significant 63% increase. All postsurvey respondents agreed or strongly agreed that the exercise would change their MCI clinical practice. Discussion: The two-team format allows comparison of how different teams handle MCI triage, and active observation allows comparison of audience and team decision making.