Schilaty, Nathan D

Anterior cruciate ligament (ACL) injury videos estimate that rupture occurs within 50 milliseconds of initial contact, but are limited by imprecise timing and nondirect data acquisition. The objective of this study was to precisely quantify the timing associated with ligament strain during simulated landing and injury events. The hypotheses tested were that the timing of peak strain following initial contact would differ between ligaments and that peak strain timing would be independent of the injury-risk profile emulated during simulated landing. A mechanical impact simulator was used to perform landing simulations based on various injury-risk profiles that were applied to each specimen in a block-randomized order. The ACL and medial collateral ligament were instrumented with strain gauges that recorded continuously. The data from 35 lower-extremity specimens were included for analysis. Analysis of variance and Kruskal–Wallis tests were used to determine the differences between timing and profiles. The mean time to peak strain was 53 (24) milliseconds for the ACL and 58 (35) milliseconds for the medial collateral ligament. The time to peak ACL strain ranged from 48 to 61 milliseconds, but the timing differences were not significant between profiles. Strain timing was independent of injury-risk profile. Noncontact ACL injuries are expected to occur between 0 and 61 milliseconds after initial contact. Both ligaments reached peak strain within the same time frame.

Context Neck pain (NP), neck injuries, and concussions are more prevalent in female athletes than in their male counterparts. Females exhibit less neck girth, strength, and stiffness against a perturbation. As part of the clinical examination for individuals with NP, ultrasound (US)–based imaging of the cervical muscles has become common. Muscle size or thickness and stiffness can be measured with US-based B-mode and shear-wave elastography (SWE), respectively. Information on reliability, normative values, and sex differences based on US-based muscle size or thickness and stiffness in young and athletic individuals is limited. Objective To evaluate sex differences in US-based muscle size or thickness and biomechanical properties of the cervical-flexor and -extensor muscles. Design Cross-sectional study. Setting Laboratory. Patients or Other Participants A total of 13 women (age = 23.7 ± 1.9 years, height = 167.1 ± 6.1 cm, mass = 63.8 ± 5.6 kg) and 11 men (age = 25.6 ± 4.9 years, height = 178.7 ± 8.3 cm, mass = 78.9 ± 12.0 kg). Main Outcome Measure(s) The same examiner collected all measures, using US B-mode to scan the cross-sectional area and thickness of the longus colli (LC), sternocleidomastoid (SCM), cervical-extensor muscles, and upper trapezius (UT) muscle. The US SWE-mode was used to measure the stiffness of the SCM and UT. Independent t tests or Mann-Whitney U tests were calculated to determine sex differences. The intraclass correlation coefficient (ICC) measured intrarater test-retest reliability. Results Men had thicker SCMs than women (P = .01). No sex differences were present for longus colli cross-sectional area, cervical-extensor muscle thickness, or UT thickness (P > .05). In addition, no sex differences were evident for SCM (P = .302) or UT (P = .703) SWE stiffness. Reliability was good to excellent (ICC = 0.715–0.890) except for SCM SWE stiffness (ICC = 0.554). Conclusions The only sex difference was in SCM thickness. However, smaller SCMs in women did not result in less SCM SWE stiffness. We provided normative values for US-based imaging of the cervical-flexor and -extensor muscles in young and athletic men and women.

Background: A recently developed mechanical impact simulator induced an anterior cruciate ligament (ACL) rupture via the application of a combination of inverse dynamics–based knee abduction moment (KAM), anterior tibial shear force (ATS), and internal tibial rotation moment with impulsive compression in a cohort of cadaveric limbs. However, there remains an opportunity to further define the interaction of internal forces and moments at the knee and their respective influence on injury events. Purpose: To identify the influence of internal knee loads on an ACL injury event using a cadaveric impact simulator. Study Design: Controlled laboratory study. Methods: Drop-landing simulations were performed and analyzed on 30 fresh-frozen cadaveric knees with a validated mechanical impact simulator. Internal forces and moments at the knee joint center were calculated using data from a 6-axis load cell recorded on the femur during testing. Kinetic data from a total of 1083 trials that included 30 ACL injury trials were used as inputs for principal component (PC) analysis to identify the most critical features of loading waveforms. Logistic regression analysis with a stepwise selection was used to select the PCs that predicted an ACL injury. Injurious waveforms were reconstructed with selected PCs in logistic regression analysis. Results: A total of 3 PCs were selected in logistic regression analysis that developed a significant model ( P < .001). The external loading of KAM was highly correlated with PC1 (ρ < –0.8; P < .001), which explained the majority (>69%) of the injurious waveforms reconstructed with the 3 selected PCs. The injurious waveforms demonstrated a larger internal knee adduction moment and lateral tibial force. After the ACL was ruptured, decreased posterior tibial force was observed in injury trials. Conclusion: These findings give us a better understanding of ACL injury mechanisms using 6-axis kinetics from an in vitro simulator. An ACL rupture was correlated with an internal knee adduction moment (external KAM) and was augmented by ATS and lateral tibial force induced by an impact, which distorted the ACL insertion orientation. Clinical Relevance: The ACL injury mechanism explained in this study may help target injury prevention programs to decrease injurious knee loading (KAM, ATS, and lateral tibial force) during landing tasks.

Background: The existent literature has well explored knee ligament kinetics and strain at and after initial contact (IC) during landing tasks. However, little is known about knee ligament biomechanics in flight before IC. Purpose: To quantify and compare change in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) strain before IC relative to after IC. Study Design: Descriptive laboratory study. Methods: A total of 40 cadaveric specimens were analyzed after being subjected to simulated landings in a mechanical impact simulator. External joint loads of varying magnitudes were applied to mimic relative injury risk load levels from an in vivo cohort and were coupled with an impulse force to represent initial ground contact. Implanted strain gauges continually recorded ligament strain. Kruskal-Wallis tests evaluated the significance of risk level and pre- and post-IC factors, while Wilcoxon each-pair tests evaluated differences within both factors. Results: Strain responses during simulated landing tasks for the ACL ( P ≥ .545) and MCL ( P ≥ .489) were consistent after IC regardless of the level of relative injury risk simulated in each trial. Before IC, the level of injury risk kinetics applied to a specimen differentiated strain response in the ACL ( P < .001) and MCL ( P < .001), as higher risk profiles produced greater changes in ligament strain. Mean baseline strain was 4.0% in the ACL and 1.0% in the MCL. Mean change in strain from the ACL ranged from 0.1% to 3.9% pre-IC and from 2.9% to 5.7% post-IC, while the MCL ranged from 0.0% to 3.0% pre-IC and from 0.9% to 1.3% post-IC. Conclusion: Within each ligament, post-IC strain response lacked statistical differences among simulated risk profiles, while pre-IC response was dependent on the risk profile simulated. Individually, neither pre- nor poststrain changes were enough to induce ACL failure, but when combined over the course of a full landing task, they could lead to rupture. Clinical Relevance: Prevention and rehabilitation techniques should aim to limit the presence of increased risk biomechanics in flight before landing, as impulse delivery at IC is inevitable.

Objective: Fatigue due to game play is often cited as a factor in musculoskeletal injuries; however, it is unclear whether or not this view is supported by published research findings. Given the importance researchers and practitioners place on the potential effects of game play with respect to injury, it is important to understand what inferences can be drawn from the collective research in this realm. This meta-analysis will consider the time of season and segment of the game, as it relates anterior cruciate ligament (ACL), groin, and hamstring injury occurrence. Data Sources: Database searches were run in PubMed, MEDLINE, SportDiscus, CINAHL, and Ausport, in addition to the inclusion of articles identified manually. Study Selection: Search terms were chosen to identify articles related to each of the 3 injuries of interest. There were no date limitations placed on the articles, as such, all published articles listed in the databases up to November 2017 were eligible for selection if they met the search criteria. Data Extraction: Initial searches yielded 1349 articles, and this was eventually reduced to 15 articles deemed suitable for inclusion in the meta-analysis, which provided 21 data sets. Data Synthesis: Comparing the first half with the second half of the season, there were no differences in ACL, groin, or hamstring injury occurrences [ACL: odds ratio (OR), 1.27; confidence interval (CI), 0.43-3.78, groin: OR, 1.79; CI, 0.63-5.06, and hamstring: OR, 1.16; CI, 0.88-1.53]. Similarly, there were no differences in injury occurrence between the first and second halves of the game for the ACL or hamstring injuries (ACL: OR, 0.43; CI, 0.47-7.92, hamstring: OR, 0.85; CI, 0.58-1.24). Conclusions: Findings from this meta-analysis determined that time in season or time in game does not influence risk of the ACL, groin, or hamstring injury. Commonly, many studies did not provide sufficient detail to be included in the meta-analysis. Consequently, it is recommended that future studies report data related to the timing of the injury within the season or game.

Background: Both the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL) bear load during athletic tasks of landing, cutting, pivoting, and twisting. As dynamic knee valgus is a purported mechanism for ACL injury, the MCL should bear significant strain load with valgus force. Hypothesis: The intact MCL will demonstrate a significant increase in strain upon failure of the ACL at 25° of knee flexion. Study Design: Controlled laboratory study. Methods: In vivo kinetics/kinematics of 44 healthy athletic participants were measured to determine stratification of injury risk (ie, low, medium, and high) in 3 degrees of knee forces/moments (knee abduction moment, anterior tibial shear, and internal tibial rotation). These stratified kinetic values were input into a cadaveric impact simulator to assess ligamentous strain during a simulated landing task. Uniaxial and multiaxial load cells and differential variable reluctance transducer strain sensors were utilized to collect mechanical data for analysis. Conditions of external loads applied to the cadaveric limbs were varied and randomized. Results: ACL strain increased with increased dynamic knee abduction moment (χ 2 [5] = 14.123, P = .0148). The most extreme dynamic knee abduction moment condition demonstrated significantly higher ACL strain compared with lower loaded trials ( P≤ .0203). Similarly, MCL strain increased with dynamic knee abduction moment (χ 2 [5] = 36.578, P < .0001). Matched-pairs analysis compared ACL strain with MCL strain (maximum ACL strain – maximum MCL strain) and demonstrated high strain for the ACL versus the MCL ( S 177 = 6223.5, P < .0001). Conclusion: Although significant, MCL strain had minimal increase with increased dynamic knee abduction moment, and the event of ACL failure did not significantly increase MCL strain when compared with high dynamic knee abduction moment conditions in the cadaveric model. The ACL bears more strain than the MCL at increasing amounts of dynamic knee abduction moment at 25° of knee flexion, which may explain the limited concomitant MCL injury rate that can occur during a dynamic valgus collapse of the knee. Clinical Relevance: These characteristics of ACL and MCL strain are important to understand the mechanisms that drive these injuries at the knee and will improve rehabilitation and injury prevention techniques.

Background: Anterior cruciate ligament (ACL) tears and concomitant medial collateral ligament (MCL) injuries are known to occur during dynamic athletic tasks that place combinatorial frontal and transverse plane loads on the knee. A mechanical impact simulator that produces clinical presentation of ACL injury allows for the quantification of individual loading contributors leading to ACL failure. Purpose/Hypothesis: The objective was to delineate the relationship between knee abduction moment, anterior tibial shear, and internal tibial rotation applied at the knee and ACL strain during physiologically defined simulations of impact at a knee flexion angle representative of initial contact landing from a jump. The hypothesis tested was that before ACL failure, abduction moment would induce greater change in ACL strain during landing than either anterior shear or internal rotation. Study Design: Controlled laboratory study. Methods: Nineteen cadaveric specimens were subjected to simulated landings in the mechanical impact simulator. During simulations, external knee abduction moment, internal tibial rotation moment, and anterior tibial shear loads were derived from a previously analyzed in vivo cohort and applied to the knee in varying magnitudes with respect to injury risk classification. Implanted strain gauges were used to track knee ligament displacement throughout simulation. Kruskal-Wallis tests were used to assess strain differences among loading factors, with Wilcoxon each pair post hoc tests used to assess differences of magnitude within each loading. Results: Each loading factor significantly increased ACL strain ( P < .005). Within factors, the high-risk magnitude of each factor significantly increased ACL strain relative to the baseline condition ( P≤ .002). However, relative to knee abduction moment specifically, ACL strain increased with each increased risk magnitude ( P≤ .015). Conclusion: Increased risk levels of each load factor contributed to increased levels of ACL strain during a simulated jump landing. The behavior of increased strain between levels of increased risk loading was most prevalent for changes in knee abduction moment. This behavior was observed in the ACL and MCL. Clinical Relevance: Knee abduction moment may be the predominant precursor to ACL injury and concomitant MCL injury. As knee abduction occurs within the frontal plane, primary preventative focus should incorporate reduction of frontal plane knee loading in landing and cutting tasks, but secondary reduction of transverse plane loading could further increase intervention efficacy. Constraint of motion in these planes should restrict peak ACL strain magnitudes during athletic performance.

ABSTRACTThe mechanism underlying non‐contact anterior cruciate ligament (ACL) injury is multi‐factorial and still an object of debate. Computational models, in combination with in vivo and cadaveric studies, can provide valuable insight into the contribution of the different factors involved. The goal of this study was to validate four knee finite element models (two males and two females) to kinematic and strain data collected in vitro with an impact‐driven simulator and use them to assess how secondary external knee loads (knee abduction moment [KAM], anterior shear force, and internal rotation torque [ITR]) affect tibiofemoral contact forces and ACL force during impact. Four subject‐specific knee models were developed from specimen computed tomography and magnetic resonance imaging. Patellofemoral and tibiofemoral ligament properties were calibrated to match experimentally measured kinematics and ligament strain. Average root mean square errors and correlations between experimental and model‐predicted knee kinematics were below 1.5 mm and 2°, and above 0.75, respectively. Similar errors and correlations were obtained for ACL strain (< 2% and > 0.9). Model‐predicted ACL forces were highly correlated with the anterior component of the tibiofemoral contact force on the lateral plateau occurring during impact (r = 0.99), which was increased by larger KAM and ITR through the posterior tibial slope and a larger contact force on the lateral side. This study provides a better understanding of the mechanism through which secondary external knee loads increase ACL injury risk during landing. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1730–1742, 2019