Muscle Dysfunction Associated With ACL Injury and Reconstruction.

Anterior cruciate ligament (ACL) injuries occur in over 200,000 individuals per year in the United States. Quadriceps central activation failure (CAF) is a common consequence of these knee injuries, though why it presents remains elusive. Neuromuscular impairments resulting from ACL injury may not be limited to the muscles crossing the knee joint, however, though limited data are available to confirm this. The overall goal of this dissertation is to examine the muscle dysfunction associated with ACL injury and reconstruction, possible mechanisms leading to the lingering quadriceps muscle weakness after ACL reconstruction (ACLr), and to determine the immediate impacts of this weakness on the affected individual. In the first study, I sought to establish the presence of muscle dysfunction throughout the lower extremity following ACL injury and ACLr. I found that significant quadriceps and hamstrings strength deficits were present in the injured/reconstructed limb compared to the contralateral side both pre- and post-operatively, with pre-operative injured limb strength deficits also present compared to healthy individuals. There was no hip or ankle weakness, however, compared to healthy individuals. Given the presence of quadriceps weakness following ACLr, identifying the contributing factors to this muscle weakness seemed critical. Therefore, in study two I examined the contributions of quadriceps atrophy and CAF to persistent quadriceps strength impairments. Individuals who were six-months post-operatively following ACLr underwent quadriceps CAF and magnetic resonance imaging assessment. Results demonstrated that neither quadriceps CAF nor atrophy significantly contributed to the persistent quadriceps weakness in these individuals. Finally, I examined the effects of neuromuscular fatigue on quadriceps strength, CAF, and lower extremity biomechanics after ACLr. Individuals 7-10 months after ACLr demonstrated lower extremity biomechanics consistent with non-contact ACL injury risk prior to fatigue. Both ACLr and healthy individuals demonstrated greater quadriceps weakness and CAF following fatigue. Healthy individuals concurrently altered their biomechanics, potentially increasing their non-contact ACL injury risk. Surprisingly, ACLr subjects demonstrated similar, potentially injurious sagittal plane biomechanics pre- and post-fatigue, suggesting that reconstruction and/or rehabilitation are not sufficiently reducing the biomechanical risk factors for re-injury when individuals return to activity.Ph.D.KinesiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78807/1/abbeyt_1.pd

Isolated hip and ankle fatigue are unlikely risk factors for anterior cruciate ligament injury

Lower extremity neuromuscular fatigue purportedly increases anterior cruciate ligament (ACL) injury risk through promotion of extreme landing mechanics. However, the impact of fatigue on muscle groups critical to the landing strategy remains unclear. This study examined the effects of isolated hip rotator and triceps surae fatigue on lower extremity landing biomechanics. Sixteen healthy females (18–22 years) reported for testing on two occasions, with one muscle group fatigued per session. Subjects performed three single-leg landings onto a force platform pre- and post-fatigue, defined as an 80% decrease in peak torque in the targeted muscle group. Hip rotator fatigue was induced via alternating concentric contractions and triceps surae fatigue through concentric plantar flexion contractions on an isokinetic dynamometer. Initial contact (IC) kinematics and peak stance (PS) kinetics and kinematics were analyzed pre- and post-fatigue. Hip rotator fatigue increased IC ( P =0.05) and PS ( P =0.04) hip internal rotation angles. Triceps surae fatigue decreased IC knee flexion ( P =0.01) angle. Isolated hip rotator and triceps surae fatigue each produced modifications in lower limb kinematic parameters viewed as risk factors for ACL injury. These modifications, however, do not appear of sufficient magnitude to compromise ligament integrity, suggesting injury via an integrative lower extremity fatigue mechanism is more likely.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78722/1/j.1600-0838.2009.01076.x.pd

Incidence and Cost of Ankle Sprains in United States Emergency Departments

Ankle sprains represent a common injury in emergency departments, but little is known about common complications, procedures, and charges associated with ankle sprains in emergency departments

Reef response to sea-level and environmental changes during the last deglaciation: Integrated Ocean Drilling Program Expedition 310, Tahiti Sea Level

The last deglaciation is characterized by a rapid sea-level rise and coeval abrupt environmental changes. The Barbados coral reef record suggests that this period has been punctuated by two brief intervals of accelerated melting (meltwater pulses, MWP), occurring at 14.08-13.61 ka and 11.4-11.1 ka (calendar years before present), that are superimposed on a smooth and continuous rise of sea level. Although their timing, magnitude, and even existence have been debated, those catastrophic sea-level rises are thought to have induced distinct reef drowning events. The reef response to sea-level and environmental changes during the last deglacial sea-level rise at Tahiti is reconstructed based on a chronological, sedimentological, and paleobiological study of cores drilled through the relict reef features on the modern forereef slopes during the Integrated Ocean Drilling Program Expedition 310, complemented by results on previous cores drilled through the Papeete reef. Reefs accreted continuously between 16 and 10 ka, mostly through aggradational processes, at growth rates averaging 10 mm yr-1. No cessation of reef growth, even temporary, has been evidenced during this period at Tahiti. Changes in the composition of coralgal assemblages coincide with abrupt variations in reef growth rates and characterize the response of the upward-growing reef pile to nonmonotonous sea-level rise and coeval environmental changes. The sea-level jump during MWP 1A, 16 ± 2 m of magnitude in ~350 yr, induced the retrogradation of shallow-water coral assemblages, gradual deepening, and incipient reef drowning. The Tahiti reef record does not support the occurrence of an abrupt reef drowning event coinciding with a sea-level pulse of ~15 m, and implies an apparent rise of 40 mm yr-1 during the time interval corresponding to MWP 1B at Barbados. © 2012 Geological Society of America

Neural Excitability and Joint Laxity in Chronic Ankle Instability, Coper, and Control Groups

Neuromuscular and mechanical deficiencies are commonly studied in participants with chronic ankle instability (CAI). Few investigators have attempted to comprehensively consider sensorimotor and mechanical differences among people with CAI, copers who did not present with prolonged dysfunctions after an initial ankle sprain, and a healthy control group

Comparing kinematic asymmetry and lateral step-down test scores in healthy, chronic ankle instability, and patellofemoral pain syndrome female basketball players: a cross-sectional study

We aimed to understand whether ankle dorsiflexion range of motion (ROM) and dynamic knee valgus (DKV) kinematic inter-limb asymmetries would be associated with the Lateral Step-Down Test (LSD) in basketball players with chronic ankle instability (CAI), patellofemoral pain (PFP) and healthy controls (HC). An observational cross-sectional study with a between-subject design was employed. Female basketball athletes with CAI (n = 20), PFP (n = 20) and HC (n = 20) were recruited. Ankle dorsiflexion-ROM, DKV angle during a single-limb squat, and LSD quality were measured bilaterally. The Asymmetry index (ASI) was calculated to identify between-limb percentage imbalances. The correlation matrix between the tasks was calculated. Ankle dorsiflexion-ROM was less in the CAI and PFP than in the HC group regardless of limb (p < 0.001). DKV angle was greater in the CAI and PFP than in the HC group bilaterally (p < 0.001). LSDs were similar between the PFP and CAI groups (p = 0.698) but worse than the HC group (p = 0.001). The ASI showed asymmetry across all tasks (p < 0.001), with the greatest asymmetry for the DKV angle. The correlation matrix between tasks on both limbs was significant (p < 0.05). Our findings suggest significant asymmetries in ankle dorsiflexion-ROM and frontal plane knee control are present in female basketball athletes with CAI and PFP, and thus, highlights need to evaluate and reduce limb asymmetries in these populations

DNA fragility in the parallel evolution of pelvic reduction in stickleback fish

Evolution generates a remarkable breadth of living forms, but many traits evolve repeatedly, by mechanisms that are still poorly understood. A classic example of repeated evolution is the loss of pelvic hindfins in stickleback fish (Gasterosteus aculeatus). Repeated pelvic loss maps to recurrent deletions of a pelvic enhancer of the Pitx1 gene. Here, we identify molecular features contributing to these recurrent deletions. Pitx1 enhancer sequences form alternative DNA structures in vitro and increase double-strand breaks and deletions in vivo. Enhancer mutability depends on DNA replication direction and is caused by TG-dinucleotide repeats. Modeling shows that elevated mutation rates can influence evolution under demographic conditions relevant for sticklebacks and humans. DNA fragility may thus help explain why the same loci are often used repeatedly during parallel adaptive evolution

Resting state functional MRI in infants with prenatal opioid exposure-a pilot study

PURPOSE: Exposure to prenatal opioids may adversely impact the developing brain networks. The aim of this pilot study was to evaluate alterations in amygdalar functional connectivity in human infants with prenatal opioid exposure. METHODS: In this prospective IRB approved study, we performed resting state functional MRI (rs-fMRI) in 10 infants with prenatal opioid exposure and 12 infants without prenatal drug exposure at < 48 weeks corrected gestational age. Following standard preprocessing, we performed seed-based functional connectivity analysis with the right and left amygdala as the regions of interest after correcting for maternal depression and infant sex. We compared functional connectivity of the amygdala network between infants with and without prenatal opioid exposure. RESULTS: There were significant differences in connectivity of the amygdala seed regions to the several cortical regions including the medial prefrontal cortex in infants who had prenatal opioid exposure when compared with opioid naïve infants. CONCLUSION: This finding of increased amygdala functional connectivity in infants with in utero opioid exposure suggests a potential role of maternal opioid exposure on infants' altered amygdala function. This association with prenatal exposure needs to be replicated in future larger studies

Investigating the effect of child maltreatment on early adolescent peer-on-peer sexual aggression: testing a multiple mediator model in a non-incarcerated sample of Danish adolescents

Objective: The aim of the present study was to investigate the relationship between child maltreatment and severe early adolescent peer-on-peer sexual aggression, using a multiple mediator model. Methods: The study comprised 330 male Grade 9 students with a mean age of 14.9 years (SD=0.5). Results: Estimates from the mediation model indicated significant indirect effects of child physical abuse on sexual aggression via peer influence and insecure-hostile masculinity. No significant total effect of child sexual abuse and child neglect on sexual aggression was found. Conclusions: Findings of the present study identify risk factors that are potentially changeable and therefore of value in informing the design of prevention programs aiming at early adolescent peer-on-peer sexual aggression in at-risk youth

Correlates of Obsessive–Compulsive Disorder in a Sample of HIV-Positive, Methamphetamine-using Men Who have Sex with Men

Substance use has been identified as a risk factor for elevated levels of obsessive–compulsive disorder (OCD). This study examined methamphetamine use and sexual risk behaviors as correlates of OCD in a sample of 245 HIV-positive men having sex with men (MSM) in San Diego, CA. In a logistic regression analysis, OCD was associated with greater frequency of methamphetamine use, more depressive symptoms, seeking out risky venues and risky sexual partners when “high” on methamphetamine, and reporting fewer sex acts in the past 2 months. These data suggest the need for increased awareness and understanding of the role that OCD may play in the drug use behaviors and risky sexual practices of methamphetamine users