Athletes who wish to resume high-level activities after an injury to the anterior cruciate ligament (ACL) are often advised to undergo surgical reconstruction. Nevertheless, ACL reconstruction (ACLR) does not equate to normal function of the knee or reduced risk of subsequent injuries. In fact, recent evidence has shown that only around half of post-ACLR patients can expect to return to competitive level of sports. A rising concern is the high rate of second ACL injuries, particularly in young athletes, with up to 20% of those returning to sport in the first year from surgery experiencing a second ACL rupture. Aside from the increased risk of second injury, patients after ACLR have an increased risk of developing early onset of osteoarthritis. Given the recent findings, it is imperative that rehabilitation after ACLR is scrutinized so the second injury preventative strategies can be optimized. Unfortunately, current ACLR rehabilitation programs may not be optimally effective in addressing deficits related to the initial injury and the subsequent surgical intervention. Motor learning to (re-)acquire motor skills and neuroplastic capacities are not sufficiently incorporated during traditional rehabilitation, attesting to the high re-injury rates. The purpose of this article is to present novel clinically integrated motor learning principles to support neuroplasticity that can improve patient functional performance and reduce the risk of second ACL injury. The following key concepts to enhance rehabilitation and prepare the patient for re-integration to sports after an ACL injury that is as safe as possible are presented: (1) external focus of attention, (2) implicit learning, (3) differential learning, (4) self-controlled learning and contextual interference. The novel motor learning principles presented in this manuscript may optimize future rehabilitation programs to reduce second ACL injury risk and early development of osteoarthritis by targeting changes in neural networks.
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Context:Up to 90% of pediatric athletes return to sport (RTS) after anterior cruciate ligament reconstruction (ACL-R); however, <50% RTS at the same level and second ACL injury rates are up to 32%.Objectives:(1) Determine which physical and patient-reported outcome measures guide clinical decision-making on RTS in pediatric athletes after ACL-R and (2) present a framework with insights from cognitive and neurophysiological domains to enhance rehabilitation outcomes.Data Sources:PubMed, CINAHL, Embrase, and Cochrane library databases and gray literature.Study Selection:Data on pediatric (<18 years) ACL-R patients, RTS, tests, and decision-making were reported in 1214 studies. Two authors independently reviewed titles and abstract, excluding 962 studies. Gray literature and cross-reference checking resulted in 7 extra studies for full-text screening of 259 studies. Final data extraction was from 63 eligible studies.Study Design:Scoping review.Level of Evidence:Level 4.Data Extraction:Details on study population, aims, methodology, intervention, outcome measures, and important results were collected in a data chart.Results:Studies included 4456 patients (mean age, 14 years). Quadriceps and hamstring strength (n = 25), knee ligament arthrometer (n = 24), and hop tests (n = 22) were the most-reported physical outcome measures guiding RTS in <30% of studies with cutoff scores of limb symmetry index (LSI) ≥85% or arthrometer difference <3 mm. There were 19 different patient-reported outcome measures, most often reporting the International Knee Documentation Committee (IKDC) (n = 24), Lysholm (n = 23), and Tegner (n = 15) scales. Only for the IKDC was a cutoff value of 85% reported.Conclusion:RTS clearance in pediatric ACL-R patients is not based on clear criteria. If RTS tests were performed, outcomes did not influence time of RTS. Postoperative LSI thresholds likely overestimate knee function since biomechanics are impaired despite achieving RTS criteria. RTS should be considered a continuum, and biomechanical parameters and contextual rehab should be pursued with attention to the individual, task, and environment. There is a need for psychological monitoring of the ACL-R pediatric population.
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Primary anterior cruciate ligament (ACL) injury prevention programs effectively reduce ACL injury risk in the short term. Despite these programs, ACL injury incidence is still high, making it imperative to continue to improve cur- rent prevention strategies. A potential limitation of current ACL injury prevention training may be a deficit in the transfer of conscious, optimal movement strategies rehearsed during training sessions to automatic movements required for athletic activities and unanticipated events on the field. Instructional strategies with an internal focus of attention have traditionally been utilized, but may not be optimal for the acquisition of the control of complex motor skills required for sports. Conversely, external-focus instructional strategies may enhance skill acquisition more efficiently and increase the transfer of improved motor skills to sports activities. The current article will present in- sights gained from the motor-learning domain that may enhance neuromuscular training programs via improved skill development and increased reten- tion and transfer to sports activities, which may reduce ACL injury incidence in the long term.
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Athletes in team sports have to quickly visually perceive actions of opponents and teammates while executing their own movements. These continuous actions are performed under time pressure and may contribute to a non-contact ACL injury. However, ACL injury screening and prevention programmes are primarily based on standardised movements in a predictable environment. The sports environment provides much greater cognitive demand because athletes must attend their attention to numerous external stimuli and inhibit impulsive actions. Any deficit or delay in attentional processing may contribute to an inability to correct potential errors in complex coordination, resulting in knee positions that increase the ACL injury risk. In this viewpoint, we advocate that ACL injury screening should include the sports specific neurocognitive demands.
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Although the benefits of current anterior cruciate ligament (ACL) injury prevention programmes have been demonstrated in efficacy studies, they, unfortunately, have had limited public health impact to date. For example, the incidence of ACL injuries continues to rise in adolescent athletes. Raising awareness and educating coaches and athletes is not enough to facilitate the widespread, sustained use of these programmes in the real-world setting. Considering the profound burden of ACL injuries, it is necessary to continue to improve the current ACL injury prevention programmes through co-creation. First, the uptake of the programmes should be optimized by a better appreciation and understanding of the individual, socio-cultural and environmental context (i.e., community). Second, the content of the programmes should be optimized to better reflect the demands of the sport by creating more ownership and increasing motivation (incorporating challenging, sport-specific and fun elements) with the end-users. In addition, implicit motor learning, random practice and differential learning are concepts that should be integrated when practising to obtain the most optimal results when learning or finetuning skills.
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Modifiable (biomechanical and neuromuscular) anterior cruciate ligament (ACL) injury risk factors have been identified in laboratory settings. These risk factors were subsequently used in ACL injury prevention measures. Due to the lack of ecological validity, the use of on-field data in the ACL injury risk screening is increasingly advocated. Though, the kinematic differences between laboratory and on-field settings have never been investigated. The aim of the present study was to investigate the lower-limb kinematics of female footballers during agility movements performed both in laboratory and football field environments. Twenty-eight healthy young female talented football (soccer) players (14.9 ± 0.9 years) participated. Lower-limb joint kinematics was collected through wearable inertial sensors (Xsens Link) in three conditions: (1) laboratory setting during unanticipated sidestep cutting at 40-50°; on the football pitch (2) football-specific exercises (F-EX) and (3) football games (F-GAME). A hierarchical two-level random effect model in Statistical Parametric Mapping was used to compare joint kinematics among the conditions. Waveform consistency was investigated through Pearson's correlation coefficient and standardized z-score vector. In-lab kinematics differed from the on-field ones, while the latter were similar in overall shape and peaks. Lower sagittal plane range of motion, greater ankle eversion, and pelvic rotation were found for on-field kinematics (p < 0.044). The largest differences were found during landing and weight acceptance. The biomechanical differences between lab and field settings suggest the application of context-related adaptations in female footballers and have implications in ACL injury prevention strategies. Highlights: Talented youth female football players showed kinematical differences between the lab condition and the on-field ones, thus adopting a context-related motor strategy. Lower sagittal plane range of motion, greater ankle eversion, and pelvic rotation were found on the field. Such differences pertain to the ACL injury mechanism and prevention strategies. Preventative training should support the adoption of non-linear motor learning to stimulate greater self-organization and adaptability. It is recommended to test football players in an ecological environment to improve subsequent primary ACL injury prevention programmes.
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Anterior cruciate ligament (ACL) injury prevention programs have been successful in the short term. Motor learning strategies with an internal focus (IF) to body movements have traditionally been utilized, but may be less suitable than an external focus (EF) for the acquisition and control of complex motor skills required for sport. To investigate the available literature and provide an overview of the effect of IF and EF instructions on jump landing technique. Systematic searches were conducted in PubMed (1966 to May 2014), CINAHL (1981 to May 2014) and PsycInfo (1989 to May 2014). A priori defined inclusion criteria were: (i) full text; (ii) published in English, German or Dutch; (iii) healthy adult subjects (mean age !18 years); (iv) jump and landing performance tested and (v) study used comparison between an EF and IF. Performance (jump height and distance) and technique (kinematics and kinetics) were the pri- mary outcome variables of interest. Nine papers were included. Significant better motor performance and movement technique was found with an EF compared to an IF. Considering the beneficial results in the included studies when utilizing an EF, it is suggested to implement these strategies into ACL injury prevention programs.
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The seventh ACL Research Retreat was held March 19–21, 2015, in Greensboro, North Carolina. The retreat brought together clinicians and researchers to present and discuss the most recent advances in anterior cruciate ligament (ACL) injury epidemiology, risk factor identification, and injury risk screening and prevention strategies. Subsequently, our goal was to identify important unknowns and future research directions. The ACL Research Retreat VII was attended by 64 clinicians and researchers from Australia, Canada, India, Ireland, the Netherlands, South Africa, the United States, and the United Kingdom. The meeting featured 3 keynote and 29 podium presentations highlighting recent research. Keynotes were delivered by Bruce Beynnon, PhD (Univer- sity of Vermont), Charles ‘‘Buz’’ Swanik, PhD, ATC (University of Delaware), and Mark Paterno, PhD, PT, ATC, SCS (Cincinnati Children’s Hospital Medical Cen- ter), addressing their ongoing work related to sex-specific multivariate risk factor models for ACL injury,1 the role of the brain in noncontact ACL injury,2 and the incidence and predictors of a second ACL injury after primary ACL reconstruction and return to sport,3 respectively. Podium and poster presentations were organized into thematic sessions of prospective and case-control risk factor studies, anatomical and hormonal risk factors, neuromuscular and biomechanical risk factors, injury risk assessment after ACL injury, and injury-prevention strategies. Time was provided for group discussion throughout the conference. At the end of the meeting, attendees participated in 1 of 3 breakout sessions on the topics of genetic, hormonal, and anatomical risk factors; neuromechanical contributions to ACL injury; and risk factor screening and prevention. From these discussions, we updated the 2012 consensus state- ment4 to reflect the most recent advances in the field and to revise the important unknowns and future directions necessary to enhance our understanding of ACL injury. Following are the updated consensus statement, keynote presentation summaries, and free communication abstracts organized by topic and presentation order.
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The aim of the present study was to investigate if the presence of anterior cruciate ligament (ACL) injury risk factors depicted in the laboratory would reflect at-risk patterns in football-specific field data. Twenty-four female footballers (14.9 ± 0.9 year) performed unanticipated cutting maneuvers in a laboratory setting and on the football pitch during football-specific exercises (F-EX) and games (F-GAME). Knee joint moments were collected in the laboratory and grouped using hierarchical agglomerative clustering. The clusters were used to investigate the kinematics collected on field through wearable sensors. Three clusters emerged: Cluster 1 presented the lowest knee moments; Cluster 2 presented high knee extension but low knee abduction and rotation moments; Cluster 3 presented the highest knee abduction, extension, and external rotation moments. In F-EX, greater knee abduction angles were found in Cluster 2 and 3 compared to Cluster 1 (p = 0.007). Cluster 2 showed the lowest knee and hip flexion angles (p < 0.013). Cluster 3 showed the greatest hip external rotation angles (p = 0.006). In F-GAME, Cluster 3 presented the greatest knee external rotation and lowest knee flexion angles (p = 0.003). Clinically relevant differences towards ACL injury identified in the laboratory reflected at-risk patterns only in part when cutting on the field: in the field, low-risk players exhibited similar kinematic patterns as the high-risk players. Therefore, in-lab injury risk screening may lack ecological validity.
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Purpose Adding external focus of attention (EF, focus on the movement effect) may optimize current anterior cruciate ligament (ACL) injury prevention programmes. The purpose of the current study was to investigate the effects of an EF, by a visual stimulus and an internal focus, by a verbal stimulus during unexpected sidestep cutting in female and male athletes and how these effects remained over time. Methods Ninety experienced basketball athletes performed sidestep cutting manoeuvres in three sessions (S1, S2 and S3). In this randomized controlled trial, athletes were allocated to three groups: visual (VIS), verbal (VER) and control (CTRL). Kinematics and kinetics were collected at the time of peak knee frontal plane moment. Results Males in the VIS group showed a larger ver- tical ground reaction force (S1: 25.4 ± 3.1 N/kg, S2: 25.8 ± 2.9 N/kg, S3: 25.2 ± 3.2 N/kg) and knee flexion moments (S1: −3.8 ± 0.9 Nm/kg, S2: −4.0 ± 1.2 Nm/ kg, S3: −3.9 ± 1.3 Nm/kg) compared to the males in the VER and CTRL groups and to the females in the VIS group (p < 0.05). Additionally, the males in the VIS group reduced knee valgus moment and the females in the VER group reduced knee varus moment over time (n.s.). Conclusion Male subjects clearly benefit from visual feedback. Females may need different feedback modes to learn a correct movement pattern. Sex-specific learning preferences may have to be acknowledged in day by day practice. Adding video instruction or feedback to regular training regimens when teaching athletes safe movement patterns and providing individual feedback might target suboptimal long-term results and optimize ACL injury prevention programmes. Level of evidence I.
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