Another monthly addition of my articles of the month! These articles cover sports-related concussion, repetitive head impacts, ACL injury risk, and the relationship between cognition and neuromotor performance.
Summary: Large prospective study of nearly 5,000 athletes that determined musculoskeletal injury rate was 87% greater in athletes who reported a prior sports-related concussion (SRC) within the previous 12 months. Interesting, this relationship was only present in non-contact, acute musculoskeletal injuries after SRC.
Summary: Individuals with a history of ACLR and matched controls completed neurocognitive testing, a lower extremity proprioception assessment, measures of dynamic lower extremity control, and neuroimaging. Increased visual cognition was associated with better proprioception and decreased time to stability during the jump-landing. Visual cognition was also associated with increased activation in brain regions related to sensory processing and motor control.
Summary: Knee biomechanics have been heavily studied as it relates to noncontact knee injuries in athletes. In this review, knee kinematics and kinetics were not associated with injury. This may be due to biomechanical assessments often ignoring any sort of cognitive constraint (e.g, temporal, space, obstacles) that is commonly seen in a sporting environment.
Summary: This was the first investigation to examine the relationship between repetitive head impacts and cervical spinal cord white matter integrity. White matter tracts associated with balance and postural control were most negatively affected following one season of football. Subsequent studies following concussive events may provide greater insight into the neural underpinnings of greater risk for lower extremity injury post-SRC.
Summary: A seminal paper defining various constructs of sports injury occurrence, data analysis, and injury risk factors and prevention. Recommended reading for anyone involved in sports injury research and clinical practice.
Summary: While there have been previous lower extremity injury surveillance datasets conducted in a variety of athletes post-concussion, this article was the first to demonstrate a specific relationship between concussion and ACL injury. Those with a concussion history in the previous 3 years were 1.6x more likely to sustain and ACL injury compared to controls. About half of the total cases examined in this study were due to sport.
Summary: Injury prediction is the holy grail of sports science. This article provides a nice overview of why current injury prediction methods are flawed (namely due to cross-sectional nature of screening) and provides opportunities to improve our models.
Summary: This article reviews biomechanical and physiological adaptations that occur after ACL injury and offers integrated strategies to restore motor control post-ACLR. Commentary is provided through perspectives including neuroscience, biomechanics, motor control/learning, and psychology.
Summary: One of the first articles to demonstrate the influence of neurocognition on musculoskeletal injury. Collegiate athletes who sustained a noncontact ACL injury performed worse on assessments of reaction time, working memory, and processing speed compared to matched controls.
Summary: This paper offers possible neuromuscular explanations for increased risk of musculoskeletal injury after concussion. Neuromuscular control post-concussion may be better understood by utilizing dynamic tasks during clinical rehabilitation, including gait and/or sport-specific scenarios.
Julia Maietta is currently a Doctoral Student in Clinical Psychology at the University of Nevada, Las Vegas (UNLV) studying the psychometric properties of the ImPACT, a commonly utilized sport concussion assessment.
Meredith Chaput is residency trained sports physical therapist who is currently a PhD student at Ohio University primarily interested in reintegrating the brain into return to sport decisions after ACL injury.
Over the last decade or so, we have seen an exponential rise in research and media attention pertaining to sports-related concussions (SRCs). And for good reason, as it is estimated that upwards of 4 million SRCs occur each year in the United States alone. I’ve previously written about the newfound association between SRC and lower extremity injuries (https://rebelmovement.org/2018/11/15/sport-related-concussion-and-lower-extremity-injury/), but in this blog series I want to take a much deeper dive into SRCs themselves, particularly on the latest research and clinical practices. Fair warning: SRCs are a difficult injury to study and manage due to the heterogeneous nature of symptomology and recovery. Simply put, there are still a lot of unknowns, but I hope this blog post gives you an idea of our current knowledge base and where we are heading in the future. Feel free to reach out via Twitter (@JasonAvedesian) or email (email@example.com) in you want to talk more about SRCs!
SRC Injury Incidence
A good starting point is to discuss the incidence of SRCs. Contact-centric sports such as football, rugby, ice hockey, and soccer make up the majority of SRCs across all levels of competition. Recent reports suggest that SRCs account for 9.6% and 4.0% of total injuries in youth and high school football athletes, respectively.10 Overall, SRCs comprise approximately 6.2% of total injuries sustained in NCAA athletes,24 and certain sports such as basketball and lacrosse have seen the rates of SRCs nearly double compared to the previous 15 years.7 Athletes appear to be at the greatest risk for SRC during competitions, as recently it has been reported that male and female collegiate soccer athletes were at a 5.54 and 9.05 times greater risk for an in-game SRC versus one sustained in practice.24 Across 20 high school sports, investigators recently reported an incidence rate of 10.37 SRCs per 10,000 athletic exposures in competition versus a 2.04 SRCs per 10,000 athletic exposures during practice.18 Furthermore, over three-quarters of collegiate athletes report an SRC during the in-season sport phase, with the majority (61.4%) occurring in competition.7 It is speculated that a more aggressive playing style and a higher frequency of head impacts during games, compared to practice, may lead to this increased risk for SRC.22
Physiological Mechanisms of SRC
An SRC is typically viewed as a functional injury rather than an injury with both functional and structural damages. Once an athlete sustains an SRC, a cascade of neurometabolic events occur in an attempt to restore ionic balance within the injured brain.12 A release of glutamine and aspartate may lead to cell permeability alterations that damage and ultimately kill the cell.13 The aforementioned amino acids lead to potassium ions exiting the cell, while a sodium and calcium influx occurs, thereby changing cellular pH levels and causing the blood vessels to constrict.11 An “energy crisis” occurs as the brain requires increased glucose metabolism to restore membrane potential, all while being in a state of reduced cerebral blood.11 This mismatch in energy supply and demand is thought to express itself through acute psychological and motor behavior changes commonly seen in concussed athletes.11
SRCs general reflect a pathophysiological disturbance rather than an injury readily seen on standard neuroimaging measures. As such, traditional medical imaging techniques (e.g. CT scans) may not demonstrate the sensitivity to detect micro alterations following a concussive event. However, recent medical advances have allowed researchers to gain further insight into the subtle, yet lingering physiological alterations that occur following an SRC. These techniques include functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), transcranial magnetic stimulation (TMS), fluid biomarkers, and brain metabolites. During verbal and visual memory tasks, symptomatic and asymptomatic male athletes demonstrated significantly less activation of the dorsolateral prefrontal cortex,5,6 a brain region associated with working memory performance. More recently, previously concussed athletes have demonstrated increased activation of various brain regions (right/left dorsolateral prefrontal cortex and cerebellum) during spatial processing tasks versus controls, potentially indicative of cortical compensation to match performance of those without a concussive history.23 Even in the absence of a diagnosed SRC, researchers have seen abnormal white matter characteristics within the brain that is linked to worse memory performance following a single season of high school football.8 Utilizing DTI and magnetic resonance, female athletes who sustained an SRC displayed abnormalities within the primary motor cortex, white matter tract, and corticospinal tract compared to non-concussed athletes.4 Most concerning, imaging was performed in symptom-free athlete on average 18.9 months post-SRC, suggesting chronic impairments in decision-making and motor execution.4 Various TMS studies have also shown that post-concussive athletes demonstrate an elevated cortical silent period, a mechanisms of motor cortex inhibition. Prolonged cortical silent period has been shown both acutely (i.e. 8 weeks)20 and chronically (i.e. 19 months)9 following a concussive event.
Overall, it does appear that post-concussive athletes demonstrate physiological alterations beyond traditional clinical resolution (i.e. symptom free, return to baseline on cognitive / balance assessments). While the aforementioned techniques offer promise for SRC diagnosis and management, much remains in terms of clinical validation and establishing appropriate monitoring protocols. For example, there is a severe lack of longitudinal study within the imaging literature that currently limits our understanding of when(if?) physiological recovery occurs following an SRC.17
Head Impact Biomechanics and SRC Risk
To ascertain biomechanical mechanisms of SRC, researchers have conducted head impact studies in a variety of sporting populations. The proposed rationale for analyzing variables such as linear and rotational head acceleration during impact events is that “thresholds” for a concussive event can be determined, along with the analysis of total “subconcussive” impacts that an athlete may sustain over the course of a practice, game, and/or season. We know with great certainty that many SRCs go unreported, therefore, measuring head accelerations in real-time may provide us with an objective tool to immediately pull an athlete from the field and conduct a clinical evaluation if an SRC is suspected. There are a few different impact sensor systems, including (1) multi-sensor units placed in the helmet; (2) a single sensor attached to the skin (forehead or neck); (3) sensor-equipped mouthguards. While these sound like a great devices to add to the SRC assessment toolbox, there are some significant limitations that I will address at the end of this section.
Unsurprisingly, football and soccer athletes sustain thousands of head impacts (defined as greater than 10g) each season.15,22 Most head impacts in collegiate athletes range between 20–30g,14 although significantly greater head accelerations, at a more frequent rate, are sustained in competition versus practice.22 While impacts located on the front, side, and top of the head are associated with higher risk for SRC,2 the frequency and location in which an athlete receives a head impact may be affected by their visual and sensory performance.16
There does appear to be a negative cumulative effect of head impacts in the absence of a diagnosed SRC. In non-concussed high school football athletes, those with demonstrated cognitive performance declines sustained a significantly greater amount of median head impacts versus counterparts without change in cognitive performance (1103 versus 438 head impacts).1 Researchers have also demonstrated a dose-response relationship between cumulative head impacts and cognitive impairments following the completion of an athletic career. In a cohort of former high school and collegiate football players, 1,800–2,400 cumulative head impacts were found to be significant thresholds for risk of developing depression, with an additional 2,800 impacts associated with a 2x risk for later life neurological consequences such as white matter brain changes.21
There are some strong limitations with the current head impact technology. First, helmet impact sensor systems assume that the helmet and skull move as a single body, therefore, improper helmet fit may overestimate true acceleratory values. Presently, there is limited data on the accuracy of single sensor systems; it’s unclear if these sensors can differentiate between received head impacts versus those due to purposeful neck motion. The biggest issue surrounding impact sensor technology is that researchers have been unable to determine a distinct head impact threshold leading to an SRC, as athletes may be concussed following a wide range of recorded head accelerations during sport.3 For example, Mihalik et al. (2017) found that “diagnosed concussion impacts ranged from 40.3g to 173.22g in linear acceleration and 163.35 to 15393.07 rad/s2 in rotational acceleration” while “noninjury impacts ranged from 10.00g to 350.00g in linear acceleration and 0.15 to 30,601.02 rad/s2.19 Simply put, there are many influential risk factors that these impact devices cannot account for, including head impact / SRC history, gender, and anthropometric measures.
As you can see, there is a lot to unpack with this complex injury. Hopefully this gives you a better understanding of SRC from an incidence and physiological / biomechanical perspective. This wraps up Part 1 in our SRC deep dive. Stay tuned for more coming soon!
Breedlove EL, Robinson M, Talavage TM, et al. Biomechanical correlates of symptomatic and asymptomatic neurophysiological impairment in high school football. Journal of Biomechanics. 2012;45(7):1265-1272.
Broglio SP, Schnebel B, Sosnoff JJ, et al. Biomechanical properties of concussions in high school football. Med Sci Sports Exerc. 2010;42(11):2064-2071.
Brolinson PG, Manoogian S, McNeely D, Goforth M, Greenwald R, Duma S. Analysis of linear head accelerations from collegiate football impacts: Current Sports Medicine Reports. 2006;5(1):23-28.
Chamard E, Lassonde M, Henry L, et al. Neurometabolic and microstructural alterations following a sports-related concussion in female athletes. Brain Injury. 2013;27(9):1038-1046.
Chen J, Johnston KM, Collie A, McCrory P, Ptito A. A validation of the post-concussion symptom scale in the assessment of complex concussion using cognitive testing and functional MRI. J Neurol Neurosurg Psychiatry. 2007;78(11):1231-1238..
Chen J-K, Johnston KM, Frey S, Petrides M, Worsley K, Ptito A. Functional abnormalities in symptomatic concussed athletes: an fMRI study. Neuroimage. 2004;22(1):68-82.
Covassin T, Moran R, Elbin RJ. Sex differences in reported concussion injury rates and time loss from participation: An update of the National Collegiate Athletic Association Injury Surveillance Program from 2004–2005 through 2008–2009. Journal of Athletic Training. 2016;51(3):189-194.
Davenport EM, Whitlow CT, Urban JE, et al. Abnormal white matter integrity related to head impact exposure in a season of high school varsity football. Journal of Neurotrauma. 2014;31(19):1617-1624.
De Beaumont L, Mongeon D, Tremblay S, et al. Persistent motor system abnormalities in formerly concussed athletes. Journal of Athletic Training. 2011;46(3):234-240..
Dompier TP, Kerr ZY, Marshall SW, et al. Incidence of concussion during practice and games in youth, high school, and collegiate American football players. JAMA Pediatr. 2015;169(7):659.
Giza CC, Hovda DA. The new neurometabolic cascade of concussion: Neurosurgery. 2014;75:S24-S33.
Giza CC, Kutcher JS. An introduction to sports concussions: Lifelong Learning in Neurology. 2014;20:1545-1551.
Grady MF. Concussion in the Adolescent Athlete. Current Problems in Pediatric and Adolescent Health Care. 2010;40(7):154-169.
Guskiewicz KM, Mihalik JP. Biomechanics of sport concussion: Quest for the elusive injury threshold. 2011;39(1):9.
Gysland SM, Mihalik JP, Register-Mihalik JK, Trulock SC, Shields EW, Guskiewicz KM. The relationship between subconcussive impacts and concussion history on clinical measures of neurologic function in collegiate football players. Ann Biomed Eng. 2012;40(1):14-22.
Harpham JA, Mihalik JP, Littleton AC, Frank BS, Guskiewicz KM. The effect of visual and sensory performance on head impact biomechanics in college football players. Ann Biomed Eng. 2014;42(1):1-10.
Kamins J, Bigler E, Covassin T, et al. What is the physiological time to recovery after concussion? A systematic review. Br J Sports Med. 2017;51(12):935-940.
Kerr ZY, Chandran A, Nedimyer AK, Arakkal A, Pierpoint LA, Zuckerman SL. Concussion incidence and trends in 20 high school sports. Pediatrics. 2019;144(5):e20192180.
Mihalik JP, Lynall RC, Wasserman EB, Guskiewicz KM, Marshall SW. Evaluating the “threshold theory”: Can head impact indicators help? Med Sci Sports Exerc. 2017;49(2):247-253..
Miller NR, Yasen AL, Maynard LF, Chou L-S, Howell DR, Christie AD. Acute and longitudinal changes in motor cortex function following mild traumatic brain injury. Brain Injury. 2014;28(10):1270-1276.
Montenigro PH, Alosco ML, Martin BM, et al. Cumulative head impact exposure predicts later-life depression, apathy, executive dysfunction, and cognitive impairment in former high school and college football players. Journal of Neurotrauma. 2017;34(2):328-340.
Reynolds BB, Patrie J, Henry EJ, et al. Effects of sex and event type on head impact in collegiate soccer. Orthopaedic Journal of Sports Medicine. 2017;5(4):232596711770170.
Slobounov SM, Zhang K, Pennell D, Ray W, Johnson B, Sebastianelli W. Functional abnormalities in normally appearing athletes following mild traumatic brain injury: a functional MRI study. Exp Brain Res. 2010;202(2):341-354..
Zuckerman SL, Kerr ZY, Yengo-Kahn A, Wasserman E, Covassin T, Solomon GS. Epidemiology of sports-related concussion in NCAA athletes from 2009-2010 to 2013-2014: Incidence, recurrence, and mechanisms. Am J Sports Med. 2015;43(11):2654-2662.
In this blog post, I’m going to discuss sports-related concussion in adolescent athletes. I’ll also discuss the research I conducted at UNLV, in which I examined lower body injury risk in previously concussed youth athletes.
Sports-related concussions (SRCs) are a major epidemiological concern among the adolescent athletic population. The majority of SRCs in the United States are sustained by adolescents athletes (< 18 years old), as it is estimated that 1.1–1.9 million cases occur annually.3 Similarly to collegiate and professional counterparts, sports such as football, lacrosse, ice hockey, and soccer account for the highest rates of SRCs in youth athletics.1,11,16 Additionally, it appears that the risk of SRC in youths is increasing at comparable rates to older sport competitors. Over an 11 year study period consisting of 158,430 high school athletes, Lincoln et al. (2011) reported a 15.5% increase in reported SRCs, a trend similar to collegiate male football participants.19
It has been suggested that adolescent athletes require a more conservative approach to SRC management and return-to-sport.6 The majority of collegiate and professional competitors receive clinical clearance to resume sport participation 5–7 days post-SRC,13,14 however, it appears that youth athletes take longer for symptoms to resolve,7,17 as well as a return to pre-concussive performance on NP tests5 and postural control tasks9,15 compared to older individuals. While reported SRC symptoms (headache, dizziness, and difficulty concentrating) were similar across age groups, 19.5% and 16.3% of high school and adolescent football athletes required at least 30 days to resume sport, respectively, compared with 7% of collegiate competitors.10
It appears that task difficulty may influence SRC recovery trajectories in the adolescent athlete. While the majority of adolescent athletes return-to-sport within four weeks post-SRC,7 locomotor deficits may still be present when paired with a secondary cognitive task. In a study comparing adolescent (mean age = 15 years old) and young adult (mean age = 20 years old) recovery trajectories following a concussive injury, Howell et al. (2014) found that adolescents were less accurate on a Stroop task and displayed greater ML COM displacement during a dual-task walking condition compared to adolescent controls at two months post-SRC.9 These cognitive and motor deficits were not determined in the concussed young adult group when matched to their control group.9 Interestingly, Howell et al. (2018) revealed that post-concussive adolescent athletes who reported a future sports-related injury (SRC or musculoskeletal) demonstrated an approximately 8% increase in dual-task cost walking speed over a one year time period.8This recent finding suggests that while clinical clearance may be granted within a four week time period for the majority of adolescents, subtle locomotor deficits may linger beyond sport resumption and contribute to future injury risk. Presently, researchers have not be able to adequately predict indicators of prolonged recovery,20 potentially attributed to large inter-individual variances in cognitive growth and maturation among adolescents. It has been suggested that prolonged SRC recovery in the adolescent athlete may be due to various factors including continued cognitive development,10 inadequate neck strength,4 and the time to which one seeks medical care from a concussion specialist.2 In their examination of factors related to delayed recovery from SRC, Bock et al. (2015) reported that 62.3% of concussed adolescents did not seek medical care until at least one week post-injury.2 Those who were evaluated by a concussion specialist within a week of injury reported significantly shorter RTP time (median = 16 days) versus those who waited beyond one week (median = 36 days).2
Recent research suggests that concussed adolescent athletes are at a greater risk for lower body injury. In a study of 18,216 male and female high school athletes, investigators determined that lower body injury risk resulting in time-loss from sport (defined as greater than the day of injury) increased by 34% for every previous SRC.12 However, a prior SRC did not result in greater risk of a non-time loss injury, although the distinction between the lower body injury classification following an SRC in high school athletes is presently unclear.12 The mechanisms responsible for an elevated lower body injury risk post-SRC in the adolescent athlete are presently unclear, however, Reed, Taha, Monette, and Keightley (2016) found that concussed teenage hockey players performed significantly worse on isometric handgrip and squat jump tests during the symptomatic and asymptomatic time periods compared to controls.18
While neuromuscular alterations may exist beyond clinical clearance to resume sport, my doctoral research at UNLV sought to examine biomechanical patterns during drop-landing tasks in adolescent athletes with and without an SRC history. The video below is a from the UNLV 3-Minute Thesis competition (I placed second overall) and the link is from a recent interview with the UNLV Graduate College.
Essentially, I found biomechanical alterations at both the ankle and knee joints that would suggest post-concussive adolescents are at greater risk for lower body injury during landing tasks. We’re in the peer-review process for this particular study, so be on the lookout for that (hopefully) soon. I’m still attempting to determine the why post-concussive athletes are at greater risk for lower body injury well beyond symptom resolution and a (seemingly) return to baseline cognitive performance; my next research studies will be examining neuropsychological correlates to lower body injury risk in collegiate athletes who have a prior SRC history. Hopefully this will give us a better understanding of the association between SRC and lower body injury. Stay tuned…
Twitter – @JasonAvedesian
Email – firstname.lastname@example.org
Bakhos LL, Lockhart GR, Myers R, Linakis JG. Emergency Department Visits for Concussion in Young Child Athletes. PEDIATRICS. 2010;126(3):e550-e556. doi:10.1542/peds.2009-3101.
Bock S, Grim R, Barron TF, et al. Factors associated with delayed recovery in athletes with concussion treated at a pediatric neurology concussion clinic. Child’s Nervous System. 2015;31(11):2111-2116. doi:10.1007/s00381-015-2846-8.
Bryan MA, Rowhani-Rahbar A, Comstock RD, Rivara F, Seattle Sports Concussion Research Collaborative. Sports- and Recreation-Related Concussions in US Youth. PEDIATRICS. 2016;138(1):e20154635-e20154635. doi:10.1542/peds.2015-4635.
Collins MW, Kontos AP, Reynolds E, Murawski CD, Fu FH. A comprehensive, targeted approach to the clinical care of athletes following sport-related concussion. Knee Surg Sports Traumatol Arthrosc. 2014;22(2):235-246. doi:10.1007/s00167-013-2791-6.
Covassin T, Elbin RJ, Harris W, Parker T, Kontos A. The Role of Age and Sex in Symptoms, Neurocognitive Performance, and Postural Stability in Athletes After Concussion. Am J Sports Med. 2012;40(6):1303-1312. doi:10.1177/0363546512444554.
Foley C, Gregory A, Solomon G. Young age as a modifying factor in sports concussion management: what is the evidence? Curr Sports Med Rep. 2014;13(6):390-394. doi:10.1249/JSR.0000000000000104.
Halstead ME, Walter KD, Moffatt K, Council on Sports Medicine and Fitness. Sport-Related Concussion in Children and Adolescents. Pediatrics. 2018;142(6). doi:10.1542/peds.2018-3074.
Howell DR, Buckley TA, Lynall RC, Meehan WP. Worsening Dual-Task Gait Costs after Concussion and their Association with Subsequent Sport-Related Injury. Journal of Neurotrauma. 2018;35(14):1630-1636. doi:10.1089/neu.2017.5570.
Howell DR, Osternig LR, Koester MC, Chou L-S. The effect of cognitive task complexity on gait stability in adolescents following concussion. Exp Brain Res. 2014;232(6):1773-1782. doi:10.1007/s00221-014-3869-1.
Kerr ZY, Zuckerman SL, Wasserman EB, Covassin T, Djoko A, Dompier TP. Concussion Symptoms and Return to Play Time in Youth, High School, and College American Football Athletes. JAMA Pediatrics. 2016;170(7):647. doi:10.1001/jamapediatrics.2016.0073.
Lincoln AE, Caswell S V., Almquist JL, Dunn RE, Norris JB, Hinton RY. Trends in Concussion Incidence in High School Sports. The American Journal of Sports Medicine. 2011;39(5):958-963. doi:10.1177/0363546510392326.
Lynall RC, Mauntel TC, Pohlig RT, et al. Lower Extremity Musculoskeletal Injury Risk After Concussion Recovery in High School Athletes. Journal of Athletic Training. 2017;52(11):1062-6050-52.11.22. doi:10.4085/1062-6050-52.11.22.
Makdissi M, McCrory P, Ugoni A, Darby D, Brukner P. A Prospective Study of Postconcussive Outcomes after Return to Play in Australian Football. The American Journal of Sports Medicine. 2009;37(5):877-883. doi:10.1177/0363546508328118.
McCrea M, Guskiewicz KM, Marshall SW, et al. Acute Effects and Recovery Time Following Concussion in Collegiate Football Players. The Journal of the American Medical Association. 2003;290(19):2556-2563. doi:10.1001/jama.290.19.2556.
Nelson LD, Guskiewicz KM, Barr WB, et al. Age Differences in Recovery After Sport-Related Concussion: A Comparison of High School and Collegiate Athletes. Journal of athletic training. 2016;51(2):142-152. doi:10.4085/1062-6050-51.4.04.
O’Connor KL, Baker MM, Dalton SL, Dompier TP, Broglio SP, Kerr ZY. Epidemiology of Sport-Related Concussions in High School Athletes: National Athletic Treatment, Injury and Outcomes Network (NATION), 2011–2012 Through 2013–2014. Journal of Athletic Training. 2017;52(3):175-185. doi:10.4085/1062-6050-52.1.15.
Purcell L, Harvey J, Seabrook JA. Patterns of Recovery Following Sport-Related Concussion in Children and Adolescents. Clinical pediatrics. 2016;55(5):452-458. doi:10.1177/0009922815589915.
Reed N, Taha T, Monette G, Keightley M. A Preliminary Exploration of Concussion and Strength Performance in Youth Ice Hockey Players. International Journal of Sports Medicine. 2016;37(09):708-713. doi:10.1055/s-0042-104199.
Westermann RW, Kerr ZY, Wehr P, Amendola A. Increasing Lower Extremity Injury Rates Across the 2009-2010 to 2014-2015 Seasons of National Collegiate Athletic Association Football. The American Journal of Sports Medicine. 2016;44(12):3230-3236. doi:10.1177/0363546516659290.
Zemek RL, Farion KJ, Sampson M, McGahern C. Prognosticators of persistent symptoms following pediatric concussion: A systematic review. JAMA Pediatrics. 2013;167(3):259-265. doi:10.1001/2013.jamapediatrics.216.
Sport-Related Concussion and Lower Extremity Injury
In this blog, I will be discussing the primary research I am conducting for my PhD studies at the University of Nevada, Las Vegas. It has been a bit since I last posted, so I figured it would be best to provide an update of what I have been doing all semester, so I hope you enjoy! (One caveat, I’m not going to reference any literature in this piece, this will be based strictly off my knowledge of the current research. I recently submitted a literature review on this topic for peer-review with the expectation of publication in the near future. I will certainly share this heavily referenced text once that process is complete). Before I get into the nitty gritty of this post, I’d like to start with a cliff notes version of the crux of my dissertation research, which will be followed by a more in-depth analysis.
Sport-related concussions (SRCs) are now classified as a major public health crisis affecting athletes across all major sporting levels. Injury surveillance data has recently determined that compared to their non-concussed counterparts, athletes who sustain a SRC are at greater risk for lower extremity injury well beyond the resolution of traditional SRC assessment batteries. This may in part be attributed to subtle cognitive and neuromuscular deficits that are exposed during dynamic sporting tasks. However, the current literature has yet to elucidate the biomechanical movement patterns of sport-specific activities (i.e. jump-landing) post-SRC. Examination of lower extremity biomechanics after a concussive event may offer objective analysis to provide a rationale for the association between SRC and lower extremity injury risk. Therefore, the purpose of my research is to examine jump-landing biomechanics in adolescent and collegiate athletes with and without a history of SRC.
Our knowledge of SRCs have come a long way in the past few decades. Initially viewed as a lack of “mental toughness”, we are now starting to understand the short- and long-term ramifications of this injury. Millions of athletes per year will sustain a SRC across all sporting levels. While (US) football receives most of the media attention, sports such as soccer, ice hockey, and lacrosse also pose significant risk for a concussive injury. While the risk of subsequent SRCs are significantly (up to 6x) higher following a first concussive event, what many do not know is that these same athletes are at a much greater risk for a lower extremity injury (i.e., anterior cruciate ligament (ACL) tears, ankle sprains, hamstring strains, etc.) for reasons that are largely unknown at this point. Specially, concussed athletes across sporting levels (high school, collegiate, and professional) are at an approximately 1.5 – 4 times greater risk for the aforementioned injuries when compared to athletes who have not sustained a SRC. But here’s where it gets really interesting: The risk of lower extremity injuries post-SRC extends well beyond the resolution of traditional SRC reporting measures – in some cases up to a year after the initial concussive event. In order to best understand the SRC complexity, practitioners must first understand the common assessment batteries administered following such an event. Following this, I discuss why these measures may lack the precision to adequately detect an at-risk athlete for further injury, particularly to the lower extremity.
The three most common ways to assess a SRC are as follows: symptom reporting, neurocognitive evaluation, and balance / sway measures. However, there are issues with all three in terms of returning an athlete back to the field. Bearing in mind that I value all of these tools as part of a multifactorial approach to SRC assessment, it is my goal to develop methods in conjunction with these tools to mitigate further injury after a SRC. Let’s discuss.
Symptom Reporting: With symptom reporting, many athletes (especially adolescents) are unaware of the most common signs following a sustained SRC. There have been numerous studies published on the lack of SRC knowledge at the youth level and it continues to be a big problem (If interested, I can provide a few posters from the CDC HEADS UP program to share with your team!). Another issue is that some athletes will attempt to hide their symptoms in order to stay on the field, there’s a reason why approximately 50% of all SRC are believed to go unreported. This is typically the case in male contact sports, as the literature indicates that female athletes are much more likely to report a suspected SRC. What we must understand is that not every SRC is obvious. Some athletes will experience a headache that can be easily passed off as just the nature of contact sports. Others will demonstrate obvious signs such as postural imbalances, dizziness, or loss of consciousness. The main takeaway with symptom reporting is that education for athletes, parents, and coaches is an absolute must at the start of every season. Even more important is re-education throughout the year, which can be as simple as impromptu quizzes at the end of a training session.
Neurocognitive Evaluation: Neurocognitive exams can be administered with a paper-and-pencil or computerized testing module. These test batteries evaluate various neurocognitive performance indices such as verbal memory, visual memory, reaction time, and visual motor processing speed, and impulse control. While neurocognitive testing has demonstrated superior sensitivity and specificity for determination of a sustained SRC, there a few limitations that must be considered. First, there are issues with athletes “sandbagging” the baseline exam, especially those at the collegiate and professional levels. These athletes are aware of the ramifications of their baseline score, a poor score at the start makes it that much easier to surpass if a SRC were to occur mid-season. This limitation is more directed toward the paper-and-pencil exams, as the computerized modules are typically equipped with validity benchmarks. When an athlete is subjected to neurocognitive testing post-SRC, they are often administered multiple (3-5) exams within a very short time period, potentially inducing practice effects. Essentially what this means is that athletes may score higher on these exams just because they are more familiar with the test itself and may learn testing strategies to score higher. When these exams are administered to non-concussed control athletes over the same time period, baseline scores are typically surpassed. Therefore the question becomes, should concussed athletes be required to best their baseline scores in order to be cleared to play?
The last thing I want to discuss is the administration of these neurocognitive exams. Athletes are seated in a quiet room alone to minimize any distractions – almost the exact opposite of their dynamic sporting environment. This situation begs the question of the generalizability of the results given the conditions. During training and competition, athletes are required to interpret task relevant (e.g., opposition and teammate position) and irrelevant (e.g., crowd noise) environmental cues while performing complex motor tasks. Further, these tests do not account for mental or physical fatigue. An athlete may perform to “baseline” during a computerized exam, but do they demonstrate this same performance in the 4th quarter?
Balance / Sway Measures: The two most common balance and sway measures post-SRC are the Balance Error Scoring System (BESS) and Sensory Organization Test (SOT).
The BESS test is subjectively scored by the clinician as the athlete completes various stances on two surface conditions (flat and foam) with their eyes closed. Error scores are calculated (e.g., opening eyes, lifting hand off hip) for each stance condition over the course of 20 second trials. Despite athletes typically requiring a greater recovery time, BESS data has demonstrated impaired postural control up to 3-5 days post-SRC. However, recent review papers on the BESS has demonstrated inadequate reliability in a clinical setting (< 0.75), and this may be attributed to the subjective nature of the test (e.g., different clinicians analyzing the same athlete over an acute time frame) and the aforementioned practice effects from repeated testing.
On the other hand, the SOT produces objective balance scores utilizing dynamic posturography under six different stance conditions. Sensory deprivations under certain conditions allow the SOT to determine visual, vestibular and / or proprioceptive impairments. Not surprisingly, the SOT has demonstrated superior sensitivity and reliability, when compared to the BESS. Reviews of SOT data have demonstrated balance impairments up to 10 days following a SRC. However, researchers question the practicality of the SOT, again due to its analysis of static posture not representative of dynamic sporting movements. Additionally, the SOT is a very expensive tool, excluding many concussed athletes from access to this type of analysis.
So you have stated the issues…what are the solutions?
To reiterate, I believe the above-mentioned assessment tools have great clinical utility and should absolutely be implemented prior to- and post-SRC. My concern lies in the ability of these tools to translate into a dynamic sporting environment that poses a potentially heightened risk for a lower body injury post-SRC. However, recent gait analysis in concussed athletes has demonstrated locomotor deficits that extend beyond the resolution traditional SRC management tools. Post-SRC, adolescent and collegiate athletes have demonstrated slower walking speeds, greater frontal plane instability, and decreased cognitive performance as the gait task becomes increasingly difficult (e.g., performing a dual motor and/or cognitive task). Studies have also obstacle avoidance strategies during gait that suggest deficiencies in executive functioning, spatial awareness, and information processing. It is recommended that gait analysis be included within a SRC assessment protocol, but more research is warranted to determine best practices in sport. Perhaps it is best to have the athlete perform various walking tasks (i.e., forward, backward, and tandem) while implementing a cognitive task (i.e., reciting the months backwards or counting by threes).
This now brings me to my current research. Specifically, I am examining jump-landing biomechanics in adolescent and collegiate athletes with and without a history of SRC. My (current) first study is in the adolescent population. Thus far, our data has shown landing mechanics that would suggest a greater risk of injury to the lower body in those who have sustained a previous SRC. Post-SRC, athletes are demonstrating greater ground reaction forces and loading rates, increased knee valgus angles, and less sagittal knee ROM during various landing tasks. A large sample size is necessary before making any definitive conclusions, but if these patterns hold with a larger n, it may start to provide a biomechanical explanation as to why athletes are at greater risk for a lower body injury post-SRC. It has been suggested that subtle cognitive and neuromuscular impairments linger well after an athlete has been cleared for sporting participation. Biomechanical analysis of dynamic, complex movement tasks may help reveal these abnormalities that are not detected by our traditional reporting measures. The goal moving forward with these studies is to incorporate cognitive stressors during the jump-landing maneuvers to make the analysis more sport-specific. With the tools and the assistance of my current research, it is the hope that we will be able to further advance and develop appropriate lower body movement screenings that will be quintessential to any SRC toolbox. Stay tuned!
(Adolescent landing biomechanics from my first concussion study)