Publications

PURPOSE OF REVIEW: Overhand (OH) throwers demonstrate a unique motion profile of the shoulder joint complex. This manuscript reviews normal adaptations in the OH thrower and contrast findings with pathologic motion deficits.

RECENT FINDINGS: Multiple adaptations in range of motion have been associated with increased risk for arm injury. The use of a more conservative cutoff value for glenohumeral internal rotation deficit and horizontal adduction in younger throwers may help reduce injury risk. Deficits in glenohumeral internal rotation, total range of motion, shoulder flexion, and external rotation insufficiency have all been proposed as means to identify OH throwers at risk for arm injury, but conflicting evidence exists. Understanding normal adaptation due to repetitive stress of throwing is essential to effective management of these athletes. Adaptive change in bone and soft tissues is normal and contributes to the unique motion profiles expected in throwers. The causative link between normal adaptation and shoulder and elbow injury remains uncertain.

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.

BACKGROUND: Athletes have traditionally been subdivided into risk classifications for ACL injury relative to the biomechanical traits they display during landing. This investigation aimed to discern whether these separate risk classifications elicit strain differences on the ACL and MCL during landing. It was hypothesized that the higher risk simulation profiles would exhibit greater ACL strain and that the ACL would exhibit greater strain than the MCL under all conditions.

METHOD: The mechanical impact simulator was used to simulate landing on a cohort of 46 cadaveric specimens. The simulator applied external joint loads to the knee prior to impulse delivery. These loads were organized into a series of profiles derived from in vivo motion capture previously performed on a cohort of 44 athletes and represented various risk classifications. Strain gauges were implanted on the ACL and MCL and simulations performed until a structural failure was elicited. Differences were assessed with Kruskal-Wallis tests.

FINDINGS: The highest-risk profiles tended to exhibit greater peak ACL strain and change in ACL strain than the baseline- and moderate-risk profiles. Specimens that failed during lower-risk simulations expressed greater strain at these loads than specimens that completed higher-risk simulations. The ACL recorded greater strain than the MCL throughout all simulation profiles.

INTERPRETATION: This behavior justifies why neuromuscular interventions have greater impact on higher-risk athletes and supports the continued screening and targeted training of those athletes that express greater injury risk. The loading disparity between ACL and MCL justifies their limited concomitant injury rate.

BACKGROUND: Limb asymmetries, as determined through in vivo biomechanical measures, are known risk factors for anterior cruciate ligament (ACL) injury. Previous cadaveric studies have shown a lack of significant differences in ligament strain between contralateral lower extremities when identical kinematics were simulated on specimens. Recent methodological developments have applied in vivo knee kinetics to exert landing forces on cadaveric lower extremities to mimic ACL injury events, but it is unknown whether contralateral limbs fail in a consistent manner during impact simulator testing.

HYPOTHESIS: It was hypothesized that contralateral lower extremities would not exhibit side-to-side differences in ligament strains. Furthermore, it was hypothesized that failure loads and failure locations would be independent of limb dominance.

STUDY DESIGN: Controlled laboratory study.

METHODS: Fourteen pairs of cadaveric lower extremities were obtained from an anatomic donations program (8 female, 6 male; mean ± SD: age, 41.7 ± 8.1 years; mass, 86.8 ± 27.0 kg; body mass index, 29.4 ± 9.0 kg/m2). A mechanical impact simulator was used to re-create the impulse ground-reaction force generated during an in vivo landing task. Ligament strains were recorded by differential variable force transducers implanted on the ACL and medial collateral ligament (MCL).

RESULTS: No significant differences were observed in peak ACL or peak MCL strain for 5 loading conditions. Fisher exact tests of independence revealed that limb dominance was independent of both load at failure and failure location.

CONCLUSION: There were no significant differences in ACL and MCL strain values between limb sides during in vitro impact simulation testing. This finding indicates that limb dominance does not influence the failure threshold of the ACL, since there was no significant difference in failure strains. The functional mechanics of the ACL are comparable between contralateral pairs from the same healthy specimen.

CLINICAL RELEVANCE: Injury mechanisms and intra-articular mechanics cannot be ethically studied in an in vivo setting. The current study provides additional insight into limb asymmetry that is observed among athletes in clinical sports medicine settings.

BACKGROUND: Females are at an increased risk of sustaining noncontact knee ligament injuries as compared with their male counterparts. The kinetics that load the anterior cruciate ligament (ACL) are still under dispute in the literature.

PURPOSE/HYPOTHESIS: The purpose of this study was to determine whether there are differences in knee kinetics between the sexes that lead to greater ACL strain in females when similar external loads are applied during a simulated drop vertical jump landing task. It was hypothesized that female limbs would demonstrate significant differences in knee abduction moment that predispose females to ACL injury when compared with males.

STUDY DESIGN: Controlled laboratory study.

METHODS: Motion analysis data of 67 athletes who performed a drop vertical jump were collected. The kinematic and kinetic data were used to categorize tertiles of relative risk, and these values were input into a cadaveric impact simulator to assess ligamentous loads during the simulated landing task. Uni- and multiaxial load cells and differential variable reluctance transducer strain sensors were utilized to collect kinetic data and maximum ACL strain for analysis. Conditions of external loads applied to the cadaveric limbs were systematically varied and randomized. Data were analyzed with 2-way repeated-measures analysis of variance and the Fisher exact test.

RESULTS: Five kinetic parameters were evaluated. Of the 5 kinetic variables, only knee abduction moment (KAM) demonstrated significant differences in females as compared with males (F1,136 = 4.398, P = .038). When normalized to height and weight, this difference between males and females increased in significance (F1,136 = 7.155, P = .008). Compared with males, females exhibited a 10.3-N·m increased knee abduction torque at 66 milliseconds postimpact and a 22.3-N·m increased abduction torque at 100 milliseconds postimpact. For loading condition, the condition of "maximum ACL strain" demonstrated a maximum difference of 54.3-N·m increased abduction torque and 74.5-N·m increased abduction torque at 66 milliseconds postimpact.

CONCLUSION: Under the tested conditions, increased external loads led to increased medial knee translation force, knee abduction moment, and external knee moment. Females exhibited greater forces and moments at the knee, especially at KAM, when loaded in similar conditions. As these KAM loads are associated with increased load and strain on the ACL, the sex-based differences observed in the present study may account for a portion of the underlying mechanics that predispose females to ACL injury as compared with males in a controlled simulated athletic task.

CLINICAL RELEVANCE: KAM increases strain to the ACL under clinically representative loading. Additionally, this work establishes the biomechanical characteristics of knee loading between sexes.

Lower extremity musculoskeletal injuries-such as ACL injury-are common, and the majority of those injuries occur without external player contact. In order to prevent non-contact musculoskeletal injuries, athletes must rely on accurate sensory information (such as visual, vestibular, and somatosensory) and stabilize joints during athletic tasks. Previously, proprioception tests (the senses of joint position, movement, tension or force) have been examined using static tests. Due to the role of proprioception in achievement of joint stability, it is essential to explore the development of dynamic proprioception tests. In this current opinion, the basic background on proprioception is covered, and the research gaps and future directions are discussed.

A dearth of sex differences research exists in sports medicine. Although females now participate in sports medicine research, a disparity of representation still exists in the literature for female athletes. Additionally, a lack of sex difference reporting exists that ultimately leads to issues of relevancy to sex and scientific reproducibility. It is important for future research to address sex differences in research design, analysis, and report.

BACKGROUND: Female patients sustain noncontact knee ligament injuries at a greater rate compared with their male counterparts. The cause of these differences in the injury rate and the movements that load the ligaments until failure are still under dispute in the literature.

PURPOSE/HYPOTHESES: This study was designed to determine differences in anterior cruciate ligament (ACL) and medial collateral ligament (MCL) strains between male and female cadaveric specimens during a simulated athletic task. The primary hypothesis tested was that female limbs would demonstrate significantly greater ACL strain compared with male limbs under similar loading conditions. A secondary hypothesis was that MCL strain would not differ between sexes.

STUDY DESIGN: Controlled laboratory study.

METHODS: Motion analysis of 67 athletes performing a drop vertical jump was conducted. Kinetic data were used to categorize injury risk according to tertiles, and these 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 (knee abduction moment, anterior tibial shear, and internal tibial rotation) were varied and randomized. Data were analyzed using 1-way analysis of variance (ANOVA), 2-way repeated-measures ANOVA, and the Fisher exact test.

RESULTS: There were no significant differences (P = .184) in maximum ACL strain between male (13.2% ± 8.1%) and female (16.7% ± 8.3%) specimens. Two-way ANOVA demonstrated that across all controlled external load conditions, female specimens consistently attained at least 3.5% increased maximum ACL strain compared with male specimens (F1,100 = 4.188, P = .043); however, when normalized to initial contact, no significant difference was found. There were no significant differences in MCL strain between sexes for similar parameters.

CONCLUSION: When compared with baseline, female specimens exhibited greater values of ACL strain at maximum, initial contact, and after impact (33, 66, and 100 milliseconds, respectively) than male specimens during similar loading conditions, with a maximum strain difference of at least 3.5%. During these same loading conditions, there were no differences in MCL loading between sexes, and only a minimal increase of MCL loading occurred during the impact forces. Our results indicate that female patients are at an increased risk for ACL strain across all similar conditions compared with male patients.

CLINICAL RELEVANCE: These data demonstrate that female specimens, when loaded similarly to male specimens, experience additional strain on the ACL. As the mechanical environment was similar for both sexes with these simulations, the greater ACL strain of female specimens must be attributed to ligament biology, anatomic differences, or muscular stiffness.

BACKGROUND: Anterior cruciate ligament injury can disrupt one's mechanoreceptors and result in decreased proprioception such as joint position sense and ultimately altered motor function. The application of localized vibration has been used to investigate the integrity of the sensorimotor system and the mechanisms of quadriceps function after anterior cruciate ligament injury and reconstruction. The purpose of the study is to evaluate joint position sense with and without vibration and compare among anterior cruciate ligament reconstructed, contralateral, and control limbs.

METHODS: Fourteen subjects with anterior cruciate ligament reconstruction (8 males and 6 females) and fourteen control subjects (7 males and 7 females) participated in the study. Subjects sat on an isokinetic dynamometer chair with localized vibration strapped on the quadriceps tendon while visual and auditory cues were removed. Subjects were asked to remember an active target position and replicate that position actively. The absolute difference between the target and replicated trial was used as joint position sense. There were three trials at three target positions (15, 45, and 75 degrees of knee flexion) with and without vibration. The order of testing conditions was randomized. One-way analysis of variance or non-parametric equivalent (Kruskal-Wallis test) was used to compare among limbs. Significance was set at P < 0.05 a priori.

FINDINGS: There were no significant joint position sense differences among anterior cruciate ligament reconstructed, contralateral, and control limbs with or without vibration (P = 0.207-0.914).

INTERPRETATION: There are several potential reasons for the current findings: vibration-induced post effect, locations of vibration, types of vibration, and rehabilitation status. Future studies should expand the current investigation and explore both sensory and motor functions in anterior cruciate ligament reconstructed subjects.