Mechanical Analysis of a Novel 3D-printed External Fixator Design Versus Industry-standard External Fixators.

INTRODUCTION: External fixation is a critical component of orthopaedic fracture management and is used for various conditions, including trauma and pediatric orthopaedics. However, the availability and high cost of external fixation devices are a concern, especially in rural and developing countries. 3D printing technology has shown promise in reducing manufacturing costs and improving accessibility to external fixation devices. The purpose of this study was to evaluate the mechanical properties of a fully 3D-printed desktop external fixation device and compare the results with the mechanical properties of commonly used, clinically available external fixators. METHODS: A fully 3D printable external fixator was designed and printed in polylactic acid at two infill densities, 20% and 100%. The mechanical properties of the 3D-printed external fixators and several commercially available fixators were tested according to applicable sections of the American Society for Testing and Materials F1541 standard protocol in axial, medial-lateral, and anterior-posterior orientations. The primary outcomes measured included failure load, safe load, rigidity, and yield load. The mean differences between experimental and control groups were calculated using one-way analysis of variance and Tukey tests. RESULTS: The 20% infill 3D-printed construct showed poor performance compared with commercially available external fixators in all testing conditions and across most variables. The 100% infill 3D-printed construct was comparable with or superior to all commercially available devices in most testing conditions. The cost for printing a single 3D-printed 100% infill external fixator was $14.49 (United States Dollar). DISCUSSION: This study demonstrates that a low-cost desktop 3D printer can create an entirely 3D-printed external fixator that resists clinically relevant forces similar to medical-grade industry-standard external fixators. Therefore, there is potential for customizable and low-cost external fixators to be manufactured with desktop 3D printing for use in remote areas and other resource-constrained environments for fracture care.

THE EFFECT OF TIME AND SEX ON POST-ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION PSYCHOLOGICAL PATIENT REPORTED OUTCOME MEASURE SCORES.

CONTEXT: Low scores on psychological patient reported outcomes measures (PROMs), including the anterior cruciate ligament-return to sport after injury (ACL-RSI) and injury-psychological readiness to return to sport (I-PRRS), after anterior cruciate ligament (ACL) reconstruction (ACLR) have been associated with a maladaptive psychological response to injury and poor prognosis. OBJECTIVE: The purpose of this study was to assess the effect of time post-ACLR and sex on ACL-RSI and I-PRRS scores and generate normative reference curves. It was hypothesized that males would demonstrate higher ACL-RSI and I-PRRS scores than females in the first 1-year post-ACLR. DESIGN: Case series. SETTING: Outpatient sports medicine and orthopedic clinic. PATIENTS: 507 patients post-primary ACLR 12-to-30-years-old with 796 ACL-RSI or I-PRRS scores one or more times between 0- and 1-year post-ACLR (age at ACLR: 17.9 ± 3.0 y). MAIN OUTCOME MEASURES: An honest broker provided anonymous data from our institution's knee injury clinical database. Generalized additive models for location, scale, and shape and generalized least squares analyses were used to assess the effect of time post-ACLR and sex on ACL-RSI and I-PRRS scores. RESULTS: ACL-RSI and I-PRRS scores increased over time post-ACLR, and males had higher scores compared to females up until approximately five months post-ACLR with scores converging thereafter. CONCLUSIONS: Males report higher ACL-RSI and I-PRRS scores compared to females in the initial stages of rehabilitation, but scores converge between sexes at times associated with return to play following ACLR. Normative reference curves can be used to objectively appraise patients' ACL-RSI and I-PRRS scores at any time point post-ACLR. This may lead to timely identification of patients with scores or changes in scores over time post-ACLR associated with a maladaptive psychological response to injury and a poor prognosis and optimized ACLR outcomes.

Clinical shoulder measurements related to joint loads in collegiate pitchers.

Background: Pitchers are prone to upper extremity injury due to repetitive high joint loads. Clinical measures of shoulder strength and range of motion (ROM) have shown links to injury risk in pitchers, however, these factors have rarely been studied in relation to throwing joint loads. The purpose of this study was to identify which clinical ROM and isokinetic strength variables were related to peak shoulder and elbow joint torques in collegiate pitchers. Methods: Thirty-three healthy collegiate pitchers participated in this study. Fastball velocity, shoulder concentric and eccentric strength, and passive shoulder ROM variables were analyzed using a Lasso regression to determine what factors influenced shoulder internal rotation torque and elbow varus torque. Results: Fastball velocity was selected by the Lasso as indicator of increased shoulder and elbow torque. Passive shoulder external rotation ROM was also selected as an important factor in joint loading with increased shoulder external rotation ROM being related to lower joint loads. The bilateral ratio of shoulder internal rotator concentric strength was related to peak shoulder and elbow torques with an increase in the bilateral ratio of shoulder strength leading to reduced joint torques. Increases in the eccentric external rotator to concentric internal rotator strength (functional ratio) of the dominant arm and increases in dominant arm eccentric internal rotator strength were both related to increases in each joint torque. Conclusion: Results from the study indicate that pitch speed, passive shoulder external rotation ROM, and the isokinetic shoulder strength profile including internal rotator strength and functional strength ratio of pitchers are related to joint loading during the pitch and may be important to monitor in relation to injury risk and/or during rehabilitation. These results provide insight into the role that both shoulder ROM and rotator cuff strength play in the dynamic stabilization of the elbow and shoulder during pitching.

Arthroscopic Repair of the Acetabular Labrum Using an Anchor-First Modified Toggle Suture Technique.

The goal of acetabular labral repair is to restore stable contact between the labrum and acetabular rim while maintaining the anatomic suction seal. One of the challenges of labral repair is achieving proper in-round repair, so that the labrum contacts the femoral head in the native position. This technique article presents a repair method that allows for enhanced inversion of the labrum to assist with anatomic repair. Our modified toggle suture technique utilizes an anchor-first method and has various distinct technical advantages. We present an efficient and vendor-agnostic technique that allows for straight or curved guides. Similarly, the anchors may be all-suture or hard-anchor designs that accommodate suture sliding. This technique also utilizes a self-retaining hand-tied knot construct to facilitate preventing knots from migrating toward the femoral head or joint space.

3D Printed Orthopaedic External Fixation Devices: A Systematic Review.

BACKGROUND: External fixators are complex, expensive orthopaedic devices used to stabilize high-energy and complex fractures of the extremities. Although the technology has advanced dramatically over the last several decades, the mechanical goals for fracture stabilization of these devices have remained unchanged. Three-dimensional (3D) printing technology has the potential to advance the practice and access to external fixation devices in orthopaedics. This publication aims to systematically review and synthesize the current literature on 3D printed external fixation devices for managing orthopaedic trauma fractures. METHODS: The Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) protocols were followed for this manuscript with minor exceptions. PubMed, Embase, Cochrane Review, Google Scholar, and Scopus online databases were systematically searched. Two independent reviewers screened the search results based on predetermined inclusion and exclusion criteria related to 3D printing and external fixation of fractures. RESULTS: Nine studies met the inclusion criteria. These included one mechanical testing study, two computational simulation studies, three feasibility studies, and three clinical case studies. Fixator designs and materials varied significantly between authors. Mechanical testing revealed similar strength to traditional metal external fixators. Across all clinical studies, five patients underwent definitive treatment with 3D printed external fixators. They all had satisfactory reduction and healing with no reported complications. CONCLUSIONS: The current literature on this topic is heterogeneous, with highly variable external fixator designs and testing techniques. A small and limited number of studies in the scientific literature have analyzed the use of 3D printing in this area of orthopaedic surgery. 3D printed external fixation design advancements have yielded promising results in several small clinical case studies. However, additional studies on a larger scale with standardized testing and reporting techniques are needed.

The influence of modeling parameters for computing joint kinetics in adolescent and adult pitchers.

Baseball pitching is a well-studied area of sports biomechanics partially due to high upper extremity (UE) injury rates. Joint kinetics have not been linked directly to UE injury in pitchers but are often used in lieu of injury data as a proxy for injury risk. Pitchers exhibit adaptations in the throwing arm that may affect body segment inertial parameters (BSIPs); however, these are unaccounted for in traditional modelling methods and may contribute to the lack of evidence linking joint kinetics to injury. Therefore, this study aimed to describe the BSIPs of the throwing arm in adolescent and adult pitchers and compare joint kinetics computed from traditional modelling methods to those using individualised BSIPs. Forty-five pitchers underwent dual-energy X-ray absorptiometry (DXA) scans and motion capture sessions in a biomechanics laboratory. Individual BSIPs from the DXA scans were used to estimate UE joint kinetics via inverse dynamics and compared to joint kinetics computed from scaled BSIPs. Throwing arm BSIPs in pitchers were significantly different from studies of the general population. Variable levels of agreement and significant differences in joint kinetics existed between methods, indicating that using joint kinetics computed via scaled models to identify pitchers at risk of injury may be inappropriate.

Recommendations for success in biomechanics outreach.

Student engagement in science, technology, engineering, and math (STEM) through informal outreach events is critical to the current educational pipeline. National Biomechanics Day (NBD) is a STEM outreach event that is an international celebration of the science of biomechanics with the goal of introducing high school students to the field. While NBD has experienced global success and substantial growth in recent years, it is an equally rewarding and challenging endeavor to host an NBD event. In this paper, we provide recommendations and mechanisms for biomechanics professionals to support their success in hosting biomechanics outreach events. Although these guidelines are framed around hosting an NBD event, the underlying principles can apply to hosting any STEM outreach event.

Wide-Awake Hand Surgery Has Its Benefits: A Study of 1,011 Patients.

Purpose: Wide-awake local anesthesia with no tourniquet has dramatically changed hand surgery practice. Using lidocaine with epinephrine and no tourniquet has allowed many procedures to be moved from the main operating room to an in-office procedure room. Previous studies have shown that using local anesthesia is safe and cost effective, with high patient satisfaction. This study evaluated patient satisfaction and complications for the first 1,011 elective hand surgeries performed using wide-awake anesthesia in an in-office procedure room. Methods: The first 1,011 patients who underwent elective hand surgery in an in-office procedure room were surveyed regarding their satisfaction. The patients were monitored for postoperative complications. Patient survey results and complications were logged in a database and analyzed. Results: Single-digit trigger finger release was the most common procedure performed (n = 582), followed by mass excision (n = 158), multiple-digit trigger finger releases (n = 109), and carpal tunnel release (n = 41). There were 43 (4.3%) superficial skin infections, with the majority seen in single-digit trigger finger releases (n = 27). There were no deep wound infections. All infections were managed nonsurgically with oral antibiotics and local wound care. Ninety-nine percent of the patients rated the in-office procedure room experience as the same as or better than a dental visit, would recommend wide-awake anesthesia to a friend or family member, and would undergo the procedure again. Using "lean and green" hand packs saved our institution more than $65,000 and saved 18.4 tons of waste during this study period. Conclusions: Surgical procedures performed with wide-awake local anesthesia with no tourniquet in an in-office procedure room can be performed safely with a low infection rate, are cost effective, and have high patient satisfaction. Clinical relevance: Minor hand surgery done in an in-office procedure room is safe, is cost effective, and has high patient satisfaction.

Athletic Shoulder Test Differences Exist Bilaterally in Healthy Pitchers.

Background: There is a lack of valid and reliable tests that assess upper extremity strength and function for rehabilitation and injury prevention purposes in throwing athletes. The Athletic Shoulder (ASH) test has been proposed as a reliable measure of shoulder strength, but has not yet been studied in baseball pitchers. Hypothesis/Purpose: The purpose of this study was to establish values for healthy baseball pitchers performing the ASH test, compare those values with other common tests of shoulder strength and function, and compare ASH test performance bilaterally. It was hypothesized that the dominant arm would perform significantly better on the ASH test compared to the non-dominant arm. A secondary purpose of the study was to evaluate if ASH test performance was related to fastball velocity in baseball pitchers. It was hypothesized that ASH test performance would positively correlate with fastball velocity. Study Design: Cross-Sectional Study. Methods: College and high school baseball pitchers were recruited to complete shoulder range of motion (ROM), isokinetic shoulder strength, and isometric shoulder strength testing using the ASH test. The ASH test was used to assess force production as a proxy for strength bilaterally at four levels of shoulder abduction (0°, 90°, 135°, and 180°), using a force plate. Approximately one-week later subjects returned for a bullpen session where fastball velocity was recorded with a radar gun. Bilateral differences in passive ROM, isokinetic, and isometric shoulder strength were examined using paired t-tests while linear relationships between isometric shoulder strength and fastball velocity were assessed using Pearson correlations. Results: Thirty-five healthy pitchers participated in the study (19.7 ± 1.8 years). Pitchers demonstrated significantly greater isometric shoulder strength at the 90° and 135° abduction positions with the throwing arm compared to the non-throwing arm. Pitchers also demonstrated commonly observed musculoskeletal adaptations in the throwing arm such as increased passive external rotation, decreased passive internal rotation, and greater internal and external rotator strength during isokinetic testing. Peak force production during the ASH test was not related to fastball velocity. Conclusion: The ASH test is capable of detecting bilateral shoulder strength adaptations commonly observed in other clinical tests in healthy pitchers. Pitchers demonstrated greater isometric peak force during the ASH test at levels of shoulder abduction similar to those observed in pitching. While these results may be intriguing for clinical use, peak force from the ASH test was not correlated to fastball velocity in pitchers, and therefore should be used with caution for predictions in this realm. Level of Evidence: 2. Clinical Relevance: A need exists for objective measures of shoulder strength for rehabilitation and injury risk monitoring in throwing athletes that are easy to administer, have high reliability and validity, and provide minimal re-injury risk to athletes recovering from injury. What is known about the subject: Data from the ASH test has been published previously in non-throwing athletes and was shown to be valid and reliable in that group. However, the test has not been explored widely in throwing athletes who are known to have significant musculoskeletal adaptations to the throwing shoulder. What this study adds to existing knowledge: The results from this study confirm that the ASH test is sensitive enough to detect the adaptations that are present in the healthy throwing athlete's shoulder. Due to the prior proven validity and reliability and these results, the test can be used to monitor throwing arm strength and function during rehabilitation or as a pre/intra-season screening tool to help describe arm health.

Limb occlusion pressure for blood flow restricted exercise: Variability and relations with participant characteristics.

OBJECTIVE: Assess lower-extremity blood flow restricted exercise (BFR) limb occlusion pressure (LOP) variability and identify related intrinsic characteristics using a portable Delphi BFR system. DESIGN: Repeated measures. SETTING: Laboratory. PARTICIPANTS: Forty-two healthy males (n = 25) and females (n = 17) (25.8 ± 5.2 y, 1.76 ±0 .09 m, 78.9 ± 14.9 kg) completed two visits. Brachial artery blood pressure, thigh circumferences (TC), and LOP were measured supine. MAIN OUTCOME MEASURES: Linear mixed-effects models (LMM) and generalizability theory were used to evaluate LOP between legs and days, determine intrinsic characteristic relations, and assess random variance components. RESULTS: LOP was not different between legs (p = .730) or days (p = .916; grand mean = 183.7 mmHg [178.4, 189.1]). LOP varied significantly between participants (p = .011, standard error = 47.3 mmHg). 47% of LOP variance was between participants, 18% and 6% was within participants between days and legs, respectively, and 28% was associated with random error. The relative error variance was 14.4 mmHg. Pulse pressure (PP) (p = .005) and TC (p = .040) were positively associated with LOP. A LMM including PP and TC predicted LOP with a mean absolute difference of 11.1 mmHg [9.7, 12.6] compared to measured LOP. CONCLUSIONS: The relative error variance suggests that clinicians should measure LOP consistently for each patient to ensure BFR safety and effectiveness.

Is Plain Anterior-Posterior Radiograph of the Pelvis Adequate for Assessment of Radiographic Implant Migration Evaluation in Total Hip Arthroplasty?

Introduction: A commonly utilized method of measuring femoral stem migration in total hip arthroplasty (THA) on plain anteroposterior (AP) pelvis radiograph with referenced image magnification has not been rigorously evaluated. This study aims to validate the reproducibility of the methods used in this technique. Methods: A retrospective study of the standardized AP pelvis radiographs of patients who had undergone THA utilizing a Corail® femoral stem was performed from June 2012 through December 2017. Radiological evaluation (head diameter, stem length, and stem seating length) were undertaken at three clinical follow-up times. Each radiographic measurement of each radiograph was repeated five times. Outcomes investigated included inter- and intra-radiograph reproducibility evaluation and radiographic image magnification. The stem length error and stem subsidence were also evaluated. Results: Two hundred THA patients met the inclusion/ exclusion criteria. The intra-radiograph reproducibility of the stem length and head diameter measurements have at least "good" reproducibility with repeated measurements falling within 0.5 mm for both measurements. The reliability for femoral stem seating length measurements has "questionable/poor" reproducibility. The inter-radiograph reproducibility was, however, substantially lower. High level of unreliable measurements with values less than 0.0 mm for both femoral stem length errors (55%) and femoral stem subsidence (32%) measurements. Less than 45% accuracy (femoral stem length error: 33%; femoral stem subsidence: 44%) to within 3 mm error. Conclusions: This study demonstrates that the assessment of radiographic implant migration after THA made on a sequence of plain AP pelvis radiograph have poor reproducibility.Level of Evidence: III.

Dynamic Postural Stability in Active, Adolescent Males Following Repeated Bouts of Aerobic Exercise in Hot and Temperate Environments: A Pilot Study.

INTRODUCTION: Proper jump-landing neuromuscular control is crucial in mitigating lower-extremity musculoskeletal injuries. The presence of fatigue, especially in extreme environments, may degrade dynamic postural stability (DPS) and result in lower-extremity injuries. This study aimed to evaluate the influence of moderate intensity exercise in hot (HOT) and temperate (TEMP) ambient temperatures and residual effects of a previous bout on DPS during a single-legged jump-landing. It was hypothesized that the participants would display worse DPS after HOT compared to TEMP. METHODS: Six recreationally active young males (16.8 ± 0.7 year, 1.88 ± 0.12 m, 83.8 ± 19.8 kg) completed two, 60-minute bouts of exercise with 60 minutes of rest between bouts in both HOT (35°C) and TEMP (22.2°C). Heart rate and core body temperature (Tc) were monitored continuously, and DPS was assessed before and after each bout. RESULTS: The DPS time and condition effects were not identified (p > 0.05), but HOT elicited some notable (d > 0.20) increases in heart rate, Tc, and DPS compared to TEMP. CONCLUSIONS: The DPS decrements varied between subjects suggesting individual-specific etiology. Repeated bouts of exercise in HOT may place an individual at a greater risk for injury than TEMP if proper prevention strategies are not used.

The Effect of Different Combinations of Three Stacked Half-Hitches and Suture Materials on an Arthroscopic Knot in a Dry or Wet Environment.

Purpose: Evidence is lacking on the effect of different combinations of three stacked half-hitches and suture materials on the loop/ knot security of an arthroscopic knot under cyclic loading conditions. The specific aim of this study was to identify variables, such as stacked half-hitch configurations, suture materials, and testing environments, that affect knot strength and loop security under cyclic loading conditions. Methods: Two suture materials (Orthocord and ForceFiber) were used to tie five differently stacked reversing half-hitches on alternating posts (RHAP) in an arthroscopic knot condition. All knots were evaluated in both dry and wet cyclic loading tests. Results: Knots tied with three identical half-hitches stacked on the same post (Conf #1) resulted in 100% knot slippage regardless of suture material in dry environment. In the wet environment this knot configuration performed slightly better (ForceFiber: 20% survived; Orthocord: 40% survived). With knots tied with one of the half-hitches in the RHAPs reversed, a significant improvement occurred in knot holding compared to Conf #1 (p<0.05). Knots tied with the last half-hitches in the RHAPs reversed using ForceFiber were 100% secure in both test environments; whereas those tied with Orthocord had 70% and 80% security rates in the respective environments. Knots tied with two half-hitches of the RHAPs reversed demonstrated the best overall performance. Conclusion: Significant effects for both stacked half-hitch configurations and suture materials on the knot loop and knot security were observed. Caution should be used when tying the 3 RHAPs in a knot using standard arthroscopic techniques. This study may provide a solution that might improve the maximum failure loads observed between orthopaedic surgeons, and achieve better clinical outcomes. Clinical Relevance: The findings of this study indicate the importance of three reversing half-hitches on alternating posts in performing arthroscopic knot tying, and provide evidence regarding discrepancies of maximum clinical failure loads observed between orthopaedic surgeons leading to better surgical outcomes.

Prior Anterior Cruciate Ligament Reconstruction Effects on Future Total Knee Arthroplasty.

BACKGROUND: The impact of prior anterior cruciate ligament (ACL) reconstruction on total knee arthroplasty (TKA) has rarely been studied. The objective of this study was to compare intraoperative characteristics in patients who underwent TKA with pre-existing hardware from prior ACL reconstruction with a matched cohort control group. METHODS: A retrospective study of patients who had undergone primary TKA with pre-existing hardware from prior ACL reconstruction was performed from June 2012 through June 2017. These patients were 2-to-1 matched to the ACL group based on similar patient demographic and provider variables. Outcomes investigated included operative time, estimated blood loss (EBL), and postoperative complications. RESULTS: One hundred one patients met the inclusion/exclusion criteria. The mean age was 54 ± 9 years, and the mean body mass index was 32.6 ± 6.5 kg/m2. The ACL group was divided into 4 subgroups: group 1, no pre-existing hardware removed (22 TKAs); group 2, pre-existing hardware removed from the femur only (8 TKAs); group 3, pre-existing hardware removed from the tibia only (45 TKAs); and group 4, pre-existing hardware removed from both the femur and tibia (26 TKAs). There was no statistical difference in EBL and postoperative complication between the ACL group and controls. Statistical differences were detected between 2 subgroups regarding mean operative time variables: ACL group 3 (74 ± 23 minutes; control: 64 ± 21 minutes, P = .020) and group 4 (79 ± 24 minutes; control: 65 ± 19 minutes, P = .010). CONCLUSION: Hardware retained, especially on the tibia, from prior ACL reconstruction has a major impact on TKA surgical procedure operative time but not on EBL and/or complications.

Validated Predictions of Metabolic Energy Consumption for Submaximal Effort Movement.

Physical performance emerges from complex interactions among many physiological systems that are largely driven by the metabolic energy demanded. Quantifying metabolic demand is an essential step for revealing the many mechanisms of physical performance decrement, but accurate predictive models do not exist. The goal of this study was to investigate if a recently developed model of muscle energetics and force could be extended to reproduce the kinematics, kinetics, and metabolic demand of submaximal effort movement. Upright dynamic knee extension against various levels of ergometer load was simulated. Task energetics were estimated by combining the model of muscle contraction with validated models of lower limb musculotendon paths and segment dynamics. A genetic algorithm was used to compute the muscle excitations that reproduced the movement with the lowest energetic cost, which was determined to be an appropriate criterion for this task. Model predictions of oxygen uptake rate (VO2) were well within experimental variability for the range over which the model parameters were confidently known. The model's accurate estimates of metabolic demand make it useful for assessing the likelihood and severity of physical performance decrement for a given task as well as investigating underlying physiologic mechanisms.

Prediction of performance reduction in self-paced exercise as modulated by the rating of perceived exertion.

PURPOSE: Rating of perceived exertion (RPE) is a scale of exercise difficulty and has been hypothesized to be a regulator of work rate during self-pacing. The goal of this work was to develop a dynamic prediction of RPE and to characterize the control strategy employed to reduce work rate during self-paced exercise using RPE as feedback. METHODS: Training and test data were acquired from the literature to develop a linear regression of RPE as a function of four physiological variables: core temperature, mean-weighted skin temperature, metabolic rate, and integral of relative oxygen consumption (R (2) = 0.85). A thermoregulatory model was used to predict core and mean-weighted skin temperature. Utilizing self-paced cycling and running data from the literature, we characterized reductions in work rate with a proportional-derivative control algorithm with RPE as feedback. RESULTS: Bland-Altman analysis revealed the necessity to parameterize RPE equations for untrained and endurance-trained individuals. Afterwards, dynamic predictions of RPE were accurate for a wide range of activity levels and air temperatures for walking, running, and cycling (LoA and bias of 2.3 and -0.03, respectively). For self-paced exercise, the control algorithm characterized the trend and magnitude of work rate reductions for cycling and running, and showed regulated RPE to be less conservative for shorter vs. longer duration exercise. CONCLUSIONS: A novel methodology to characterize self-paced work intensity, based upon dynamic physiologic response, is provided. The complete model is a useful tool that estimates performance decrements during self-paced exercise and predicts tolerance time for exhaustive fixed-rate exercise.

A model for predicting primary blast lung injury.

BACKGROUND: This article presents a model-based method for predicting primary blast injury. On the basis of the normalized work injury mechanism from previous work, this method presents a new model that accounts for the effects of blast orientation and species difference. METHODS: The analysis used test data from a series of extensive experimental studies sponsored by the US Army Medical Research and Materiel Command. In these studies, more than 1200 sheep were exposed to air blast in free-field and confined enclosures, and lung injuries were quantified as the percentage of surface area contused. Blast overpressure data were collected using blast test devices placed at matching locations to represent loadings to the thorax. Adopting the modified Lobdell model with further modifications specifically for blast and scaling, the thorax deformation histories for the left, chest, and right sides of the thorax were calculated for all sheep subjects. Using the calculated thorax velocities, effective normalized work was computed for each test subject representing the irreversible work performed on the lung tissues normalized by lung volume and ambient pressure. RESULTS: Dose-response curves for four categories of injuries (trace, slight, moderate, and severe) were developed by performing log-logistic correlations of the computed normalized work with the injury outcomes, including the effect of multiple shots. A blast lethality correlation was also established. CONCLUSION: Validated by sheep data, the present work revalidates the previous understanding and findings of the blast lung injury mechanism and provides an anthropomorphic model for primary blast injury prediction that can be used for occupational and survivability analysis. LEVEL OF EVIDENCE: Economic and decision analysis, level III.

The influence of modeling separate neuromuscular compartments on the force and moment generating capacities of muscles of the feline hindlimb.

Functional electrical stimulation (FES) has the capacity to regenerate motion for individuals with spinal cord injuries. However, it is not straightforward to determine the stimulation parameters to generate a coordinated movement. Musculoskeletal models can provide a noninvasive simulation environment to estimate muscle force and activation timing sequences for a variety of tasks. Therefore, the purpose of this study was to develop a musculoskeletal model of the feline hindlimb for simulations to determine stimulation parameters for intrafascicular multielectrode stimulation (a method of FES). Additionally, we aimed to explore the differences in modeling neuromuscular compartments compared with representing these muscles as a single line of action. When comparing the modeled neuromuscular compartments of biceps femoris, sartorius, and semimembranosus to representations of these muscles as a single line of action, we observed that modeling the neuromuscular compartments of these three muscles generated different force and moment generating capacities when compared with single muscle representations. Differences as large as 4 N m (approximately 400% in biceps femoris) were computed between the summed moments of the neuromuscular compartments and the single muscle representations. Therefore, modeling neuromuscular compartments may be necessary to represent physiologically reasonable force and moment generating capacities of the feline hindlimb.

Biarticular hip extensor and knee flexor muscle moment arms of the feline hindlimb.

Moment arms are important for understanding muscular behavior and for calculating internal muscle forces in musculoskeletal simulations. Biarticular muscles cross two joints and have moment arms that depend on the angle of both joints the muscles cross. The tendon excursion method was used to measure the joint angle-dependence of hamstring (biceps femoris, semimembranosus and semitendinosus) moment arm magnitudes of the feline hindlimb at the knee and hip joints. Knee angle influenced hamstring moment arm magnitudes at the hip joint; compared to a flexed knee joint, the moment arm for semimembranosus posterior at the hip was at most 7.4 mm (25%) larger when the knee was extended. On average, hamstring moment arms at the hip increased by 4.9 mm when the knee was more extended. In contrast, moment arm magnitudes at the knee varied by less than 2.8 mm (mean=1.6 mm) for all hamstring muscles at the two hip joint angles tested. Thus, hamstring moment arms at the hip were dependent on knee position, while hamstring moment arms at the knee were not as strongly associated with relative hip position. Additionally, the feline hamstring muscle group had a larger mechanical advantage at the hip than at the knee joint.