A preliminary investigation of motor evoked potential abnormalities following sport-related concussion

Sub-concussive head impacts from heading footballs do not acutely alter brain excitability as compared to a control group

BACKGROUND

Repeated sub-concussive head impacts are a growing brain health concern, but their possible biomarkers remain elusive. One impediment is the lack of a randomised controlled human experimental model to study their effects on the human brain.

OBJECTIVES

This work had two objectives. The first one was to provide a randomised controlled human experimental model to study the acute effects of head impacts on brain functions. To achieve this, this work's second objective was to investigate if head impacts from heading footballs acutely alter brain excitability by increasing corticospinal inhibition as compared to a control group.

METHODS

In practised and unpractised young healthy adults, transcranial magnetic stimulation was used to assess corticospinal silent period (CSP) duration and corticospinal excitability (CSE) before and immediately after performing headings by returning 20 hand-thrown balls directed to the head (Headings; n = 30) or the dominant foot (Control; n = 30). Moreover, the Rivermead Post-Concussion Questionnaire (RPQ) was used to assess the symptoms of head impacts. Head acceleration was also assessed in subgroups of participants.

RESULTS

The intervention lengthened CSP duration in both the Headings (6.4 ± 7.5%) and Control groups (4.6 ± 2.6%), with no difference in lengthening between the two groups. Moreover, CSE was not altered by the intervention and did not differ between groups. However, performing headings increased headaches and dizziness symptoms and resulted in greater head acceleration upon each football throw (12.5 ± 1.9g) as compared to the control intervention (5.5 ± 1.3g).

CONCLUSIONS

The results suggest that head impacts from football headings do not acutely alter brain excitability as compared to a control intervention. However, the results also suggest that the present protocol can be used as an experimental model to investigate the acute effects of head impacts on the human brain.

Lower-Extremity Neuromuscular Function Following Concussion: A Preliminary Examination

CONTEXT

Neuromuscular function is altered acutely following concussion and theoretically linked to the subsequent postconcussion musculoskeletal injury risk. Existing research has only examined voluntary muscle activation, limiting mechanistic understanding. Therefore, our study aimed to examine voluntary and involuntary muscle activation between college-aged, concussed individuals when symptom-free and healthy matched controls.

DESIGN

Prospective, cross-sectional cohort laboratory study.

METHODS

Concussed and healthy participants (n = 24; 58% male, age: 19.3 [1.1] y, mass: 70.3 [16.4] kg, height: 177.3 [12.7] cm) completed the superimposed burst (SB) neuromuscular assessment on their dominant limb within 72 hours after self-reporting asymptomatic (22.4 [20.2] d postinjury). Unnormalized and bodyweight-normalized quadriceps maximal voluntary isometric contraction torque (in newton meters), unnormalized and bodyweight-normalized electrically stimulated SB torque, pain (numeric 1-10) during SB, and the central activation ratio (in percentage) were assessed via the SB. Parametric and nonparametric analyses, 95% confidence intervals (95% CIs), and Hedges g (parametric) and Spearman ρ (nonparametric) effect sizes were used to examine group differences (α = .05).

RESULTS

The maximal voluntary isometric contraction torque (concussed: 635.60 N·m [300.93] vs control: 556.27 N·m [182.46]; 95% CI, -131.36 to 290.02; P = .443; d = 0.33), SB torque (concussed: 203.22 N·m [97.17], control: 262.85 N·m [159.07]; 95% CI, -171.22 to 51.97; P = .280; d = -0.47), and central activation ratio (concussed: 72.16% [17.16], control: 70.09% [12.63]; 95% CI, -10.68 to 14.83; P = .740; d = 0.14) did not differ between the concussed and control groups regardless of bodyweight normalization (P ≥ .344). Pain during the SB was significantly higher with a medium effect for participants with a concussion versus healthy controls (concussed: median = 7, control: median = 5; P = .046; ρ = -0.42).

DISCUSSION

These findings suggest concussed participants do not have statistically altered voluntary or involuntary quadricep neuromuscular function once asymptomatic compared with controls. Therefore, the elevated postconcussion musculoskeletal injury risk may not be attributed to lower-extremity muscle activation. Concussed participants displayed greater pain perception during the SB, which suggests somatosensory or perception changes requiring further examination.

Mild traumatic brain injury and sports-related concussion

Mild traumatic brain injury (mTBI) and concussion are equivalent terms for the sequela of injury to the head that disrupts brain functioning. Various forces may be causative from seemingly innocuous bumps to the head resulting from sports-related injuries to more severe blows to the head. However, the postconcussive motor, cognitive, emotional, and psychosocial sequelae can be just as devastating and long lasting, leading to loss of independent function and safe performance of activities. Taken together, they pose a significant challenge to recovery, requiring a multifaceted dynamic rehabilitative strategy. The current systems of health care pose challenges to suboptimal management of sports-related concussion (SRC) that goes beyond the acute injury, and into the school setting, failing to be identified by school staff, and inconsistencies in communicating medical information regarding school modifications, follow-up health services, or concussion-related educational services. Children who sustain SRC at different ages face different challenges. Young children face increased vulnerability due to SRC that coincides with periods of brain motor maturation and development.

Assessment of Somatosensory and Motor Processing Time in Retired Athletes with a History of Repeated Head Trauma

Measurement of the adverse outcomes of repeated head trauma in athletes is often achieved using tests where the comparator is ‘accuracy’. While it is expected that ex-athletes would perform worse than controls, previous studies have shown inconsistent results. Here we have attempted to address these inconsistencies from a different perspective by quantifying not only accuracy, but also motor response times. Age-matched control subjects who have never experienced head trauma (n = 20; 41.8 ± 14.4 years) where compared to two cohorts of retired contact sport athletes with a history of head trauma/concussions; one with self-reported concerns (n = 36; 45.4 ± 12.6 years), and another with no ongoing concerns (n = 19; 43.1 ± 13.5 years). Participants performed cognitive (Cogstate) and somatosensory (Cortical Metrics) testing with accuracy and motor times recorded. Transcranial magnetic stimulation (TMS) investigated corticospinal conduction and excitability. Results showed that there was little difference between groups in accuracy scores. Conversely, motor times in all but one test revealed that ex-athletes with self-reported concerns were significantly slower compared to other groups (p ranges 0.031 to <0.001). TMS latency showed significantly increased time (p = 0.008) in the group with ongoing concerns. These findings suggest that incorporating motor times is more informative than considering accuracy scores alone.

Corticospinal Excitability and Inhibition Are Not Different between Concussed Males and Females

It has been consistently demonstrated that females report greater numbers of concussions in sex-comparable sports and take longer to recover from concussive symptoms than males. However, it is unknown if the neurophysiological consequences of concussion may contribute to these sex differences in concussion symptoms and recovery. The purpose of this study was to examine potential sex-related differences in neurophysiology in healthy and concussed individuals. Twenty-one (nine F) concussed individuals (20.9 ± 4.1 years; CONC) and twenty-one age-, sex-, height-, weight-, and activity-matched controls (21.2 ± 4.2 years; CONT) participated in the study. The CONC group reported to the lab within 72 h, 1-week, and 2-weeks post-injury and the CONT group followed a similar measurement schedule. Using transcranial magnetic stimulation, motor evoked potential (MEP) amplitude and cortical silent period (CSP) duration were measured from the first dorsal interosseous muscle to assess corticospinal excitability and inhibition, respectively. There were no significant differences across time (p ≥ 0.13) or between the CONC and CONT group in MEP amplitude (p = 0.72) or CSP duration (p = 0.54). Overall, males (119.08 ± 29.91 ms) had significantly longer CSP durations compared with females (101.24 ± 33.43 ms), indicating greater corticospinal inhibition in males, regardless of injury status (p = 0.04). An important and novel finding of this study was the lack of differences in these neurophysiological measures between males and females following concussion. To our knowledge, this is the first study to document greater corticospinal inhibition in males compared with females.

Concussion Is Associated With Increased Odds of Acute Lower-Extremity Musculoskeletal Injury Among National Basketball Association Players

Purpose

To determine the odds of sustaining an acute lower-extremity (LE) musculoskeletal injury during the 90-day period after return-to-play (RTP) from concussion in National Basketball Association (NBA) athletes.

Methods

Concussion data for NBA players were collected from the 1999-2000 to 2017-2018 seasons, from publicly available sources. Age, position, injury, time to RTP, and demographic factors were collected. The 90-day period after each case of concussion was reviewed for acute noncontact LE musculoskeletal injury. Control athletes without a documented history of concussion were matched to concussed athletes by age, body mass index, position, and experience. Conditional logistic regression with a calculated odds ratio and a 95% confidence interval were used to assess the association between concussion and subsequent risk of LE injury.

Results

In total, 189 concussions were documented in 153 athletes. Of these, 140 cases were the first recorded instance of concussion in players with publicly available data. Thirty-six (25.7%) athletes sustained a LE injury within 90 days of concussion; 26 (20.2%) were non–season-ending and included in RTP analysis. The odds of sustaining an acute LE musculoskeletal injury within the 90-day period after concussion was 4.69 times greater in concussed players compared with controls (95% confidence interval 1.96-11.23, P < .001). There was no significant difference in games (4.2 ± 5.0 vs 4.7 ± 4.7 games, P = .566) or days (18.5 ± 39.1 days vs 10.9 ± 10.6 days, P = .912) missed between concussed players with LE injury and nonconcussed controls. The most common LE injuries in concussed athletes were ligament sprains/tears (65%).

Conclusions

Concussed NBA athletes have increased odds for sustaining an acute LE musculoskeletal injury within 90 days of RTP compared with nonconcussed controls. The most common injuries were ligament strains or tears. Changes in neuromotor control and proprioception following a concussion should be evaluated in high-level basketball players returning to sport.

Level of Evidence

Level III, Case-Control Study.

Physiological Vibration Acceleration (Phybrata) Sensor Assessment of Multi-System Physiological Impairments and Sensory Reweighting Following Concussion

Objective

To assess the utility of a head-mounted wearable inertial motion unit (IMU)-based physiological vibration acceleration (“phybrata”) sensor to support the clinical diagnosis of concussion, classify and quantify specific concussion-induced physiological system impairments and sensory reweighting, and track individual patient recovery trajectories.

Methods

Data were analyzed from 175 patients over a 12-month period at three clinical sites. Comprehensive clinical concussion assessments were first completed for all patients, followed by testing with the phybrata sensor. Phybrata time series data and spatial scatter plots, eyes open (Eo) and eyes closed (Ec) phybrata powers, average power (Eo+Ec)/2, Ec/Eo phybrata power ratio, time-resolved phybrata spectral density (TRPSD) distributions, and receiver operating characteristic (ROC) curves are compared for individuals with no objective impairments and those clinically diagnosed with concussions and accompanying vestibular impairment, other neurological impairment, or both vestibular and neurological impairments. Finally, pre- and post-injury phybrata case report results are presented for a participant who was diagnosed with a concussion and subsequently monitored during treatment, rehabilitation, and return-to-activity clearance.

Results

Phybrata data demonstrate distinct features and patterns for individuals with no discernable clinical impairments, diagnosed vestibular pathology, and diagnosed neurological pathology. ROC curves indicate that the average power (Eo+Ec)/2 may be utilized to support clinical diagnosis of concussion, while Eo and Ec/Eo may be utilized as independent measures to confirm accompanying neurological and vestibular impairments, respectively. All 3 measures demonstrate area under the curve (AUC), sensitivity, and specificity above 90% for their respective diagnoses. Phybrata spectral analyses demonstrate utility for quantifying the severity of concussion-induced physiological impairments, sensory reweighting, and subsequent monitoring of improvements throughout treatment and rehabilitation.

Conclusion

Phybrata testing assists with objective concussion diagnosis and provides an important adjunct to standard concussion assessment tools by objectively ascertaining neurological and vestibular impairments, guiding targeted rehabilitation strategies, monitoring recovery, and assisting with return-to-sport/work/learn decision-making.

The Neurophysiological Responses of Concussive Impacts: A Systematic Review and Meta-Analysis of Transcranial Magnetic Stimulation Studies

Aim: This systematic review and meta-analysis investigated neurophysiological responses using transcranial magnetic stimulation (TMS) following a concussion or sub-concussion.

Methods: A systematic searching of relevant databases for peer-reviewed literature quantifying motor evoked potentials from TMS between 1999 and 2019 was performed. A meta-analysis quantified pooled data for measures including motor threshold, motor latency, and motor evoked potential amplitude and for inhibitory measures such as cortical silent period duration, short-interval intracortical inhibition (SICI), and long-interval intracortical inhibition (LICI) ratios.

Results: Fifteen articles met the inclusion criteria. The studies were arbitrarily classified into the groups, based on time post-concussion, “acute” (subjects 0–3 months post-injury, n = 8) and “post-acute” (3 months−2 years post-concussion, n = 7). A TMS quality of study checklist rated studies from moderate to high in methodological quality; however, the risk of bias analysis found that the included studies were categorised as high risk of bias, particularly for a lack of allocation concealment and blinding of participants in the methodologies. A meta-analysis showed no differences in excitability measures, apart from a decreased motor threshold that was observed in the concussed group (SMD −0.28, 95% CI −0.51 to −0.04; P = 0.02) for the post-acute time frame. Conversely, all inhibitory measures showed differences between groups. Cortical silent period duration was found to be significantly increased in the acute (SMD 1.19, 95% CI 0.58–1.81; P < 0.001) and post-acute (SMD 0.55, 95% CI 0.12–0.98; P = 0.01) time frames. The SICI (SMD −1.15, 95% CI −1.95 to −0.34; P = 0.005) and LICI (SMD −1.95, 95% CI −3.04 to −0.85; P = 0.005) ratios were reduced, inferring increased inhibition, for the post-acute time frame.

Conclusion: This systematic review and meta-analysis demonstrates that inhibitory pathways are affected in the acute period post-concussion. However, persistent alterations in cortical excitability remain, with increased intracortical inhibition. While TMS should be considered as a reliable technique to measure the functional integrity of the central nervous system, the high risk of bias and heterogeneity in data suggest that future studies should aim to incorporate standardised methodological techniques, particularly with threshold determination and stimulus intervals for paired-pulse measures.

Excitability, Inhibition, and Neurotransmitter Levels in the Motor Cortex of Symptomatic and Asymptomatic Individuals Following Mild Traumatic Brain Injury

Purpose: The purpose of this study was to determine the level of excitability and inhibition, as well as the concentrations of excitatory and inhibitory neurotransmitters, in the motor cortex of individuals with acute and chronic symptoms from mTBI.

Methods: Fifty-three individuals were assigned to one of four groups: (i) without history of mTBI (Control), (ii) within 72-h of diagnosis of mTBI (Acute), (iii) with history of mTBI and no remaining symptoms (Chronic Asymptomatic), and (iv) with chronic symptoms from mTBI, lasting at least 3 months post-injury (Chronic Symptomatic). Measures of corticospinal excitability and inhibition were obtained using transcranial magnetic stimulation (TMS). On the same day, measures of glutamate and GABA concentrations were obtained from the primary motor cortex (M1) using proton magnetic resonance spectroscopy.

Results: MEP amplitude and area were both significantly lower in the Chronic Symptomatic group compared to the Control and Chronic Asymptomatic groups (p ≤ 0.05). Intracortical inhibition was not significantly different among groups (p = 0.14). The concentration of glutamate in M1 was similar between groups (p = 0.93) while there was a trend for a lower concentration of GABA in the Chronic Symptomatic group compared to the Acute group (p = 0.06).

Conclusions: Individuals with chronic mTBI symptoms appear to have lower corticospinal excitability compared with acutely-injured individuals and asymptomatic controls, but the absence of differences in intracortical inhibition, and concentrations of excitatory and inhibitory neurotransmitters in M1 suggests that neurotransmitter changes in the human brain post-mTBI do not follow the pattern typically seen in the animal literature.

Altered corticomotor latencies but normal motor neuroplasticity in concussed athletes

Persistent cognitive, affective, and motor symptoms have been associated with sports-related concussions including several neurophysiological changes in the primary motor cortex. In particular, previous research has provided some evidence of altered latencies of the corticomotor pathway and altered motor neuroplasticity. However, to date, no studies have assessed these neurophysiological metrics in a common group of athletes across different phases of injury and recovery. In this study corticomotor latencies and neuroplasticity were assessed in collegiate athletes with or without a history of prior concussion across two different phases of injury: either in an acute state of concussion (within 2 wk of injury) or in a chronic state of concussion (more than 1 yr after injury). Corticomotor latencies were determined by measuring the motor evoked potential (MEP) onset time, and motor neuroplasticity was assessed by measuring MEP amplitudes following application of anodal transcranial direct current stimulation (tDCS) over the primary motor cortex (M1). We found that concussed athletes had slower corticomotor latencies than nonconcussed athletes, and corticomotor latency was also positively correlated with the number of prior concussions. In contrast, there was no evidence of altered motor neuroplasticity in athletes regardless of concussion history. These findings suggest concussions may lead to permanent changes in the corticospinal tract that are exacerbated by repeated injury.NEW & NOTEWORTHY We are the first to assess corticomotor latencies and motor neuroplasticity in a common group of collegiate athletes across different phases of injury and recovery. We found that the number of concussions an individual sustains negatively impacts corticomotor latencies with a higher number of prior concussions correlating positively with longer latencies. Our findings indicate that concussions may lead to permanent changes in the corticospinal tract that are exacerbated by repeated injury.

Understanding the Consequences of Repetitive Subconcussive Head Impacts in Sport: Brain Changes and Dampened Motor Control Are Seen After Boxing Practice

Objectives

The potential effects of exposure to repetitive subconcussive head impacts through routine participation in sport are not understood. To investigate the effects of repetitive subconcussive head impacts we studied boxers following customary training (sparring) using transcranial magnetic stimulation (TMS), decomposition electromyographic (EMG) and tests of memory.

Methods

Twenty amateur boxers performed three 3-min sparring bouts. Parameters of brain function and motor control were assessed prior to sparring and again immediately, 1 h and 24 h post-sparring. Twenty control participants were assessed following mock-sparring.

Results

One hour after sparring boxers showed increased corticomotor inhibition, altered motor unit recruitment strategies, and decreased memory performance relative to controls, with values returning to baseline by the 24 h follow up.

Conclusion

Repetitive subconcussive head impacts associated with sparring resulted in acute and transient brain changes similar to those previously reported in soccer heading, providing convergent evidence that sport-related head impacts produce a GABAergic response. These acute changes in brain health are reminiscent of effects seen following brain injury, and suggest a potential mechanism underlying the damaging long-term effects of routine repetitive head impacts in sport.

Electrophysiological testing in concussion: A guide to clinical applications

The diagnosis of mild traumatic brain injury in concussion is difficult since it is often unwitnessed, the patient’s recall is unreliable and initial clinical examination is often unrevealing, correlating poorly with the extent of brain injury. At present, there are no objective biomarkers of mild traumatic brain injury in concussion. Thus, a sensitive gold standard test is required to enable the effective and safe triage of patients who present to the acute services. As well as triage, objective monitoring of patients’ recovery over time and separate from clinical features that patients may develop following the injury (e.g. depression and migraine) is also needed. In contrast to neuroimaging, which is widely used to investigate traumatic brain injury patients, electrophysiology is readily available, is cheap and there are internationally recognized standardised methodologies. Herein, we review the existing literature on electrophysiological testing in concussion and mild traumatic brain injury; specifically, electroencephalogram, polysomnography, brainstem auditory evoked potentials, electro- and videonystagmography, vestibular evoked myogenic potentials, visually evoked potentials, somatosensory evoked potentials and transcranial magnetic stimulation.

Neuromuscular Control Deficits and the Risk of Subsequent Injury after a Concussion: A Scoping Review

An emerging area of research has identified that an increased risk of musculoskeletal injury may exist upon returning to sports after a sport-related concussion. The mechanisms underlying this recently discovered phenomenon, however, remain unknown. One theorized reason for this increased injury risk includes residual neuromuscular control deficits that remain impaired despite clinical recovery. Thus, the objectives of this review were: (1) to summarize the literature examining the relationship between concussion and risk of subsequent injury and (2) to summarize the literature for one mechanism with a theorized association with this increased injury risk, i.e., neuromuscular control deficits observed during gait after concussion under dual-task conditions. Two separate reviews were conducted consistent with both specified objectives. Studies published before 9 December, 2016 were identified using PubMed, Web of Science, and Academic Search Premier (EBSCOhost). Inclusion for the objective 1 search included dependent variables of quantitative measurements of musculoskeletal injury after concussion. Inclusion criteria for the objective 2 search included dependent variables pertaining to gait, dynamic balance control, and dual-task function. A total of 32 studies were included in the two reviews (objective 1 n = 10, objective 2 n = 22). According to a variety of study designs, athletes appear to have an increased risk of sustaining a musculoskeletal injury following a concussion. Furthermore, dual-task neuromuscular control deficits may continue to exist after patients report resolution of concussion symptoms, or perform normally on other clinical concussion tests. Therefore, musculoskeletal injury risk appears to increase following a concussion and persistent motor system and attentional deficits also seem to exist after a concussion. While not yet experimentally tested, these motor system and attentional deficits may contribute to the risk of sustaining a musculoskeletal injury upon returning to full athletic participation.

A review of the effects of physical activity and sports concussion on brain function and anatomy

Physical activity has been associated with widespread anatomical and functional brain changes that occur following acute exercise or, in the case of athletes, throughout life. High levels of physical activity through the practice of sports also lead to better general health and increased cognitive function. Athletes are at risk, however, of suffering a concussion, the effects of which have been extensively described for brain function and anatomy. The level to which these effects are modulated by increased levels of fitness is not known. Here, we review literature describing the effects of physical activity and sports concussions on white matter, grey matter, neurochemistry and cortical excitability. We suggest that the effects of sports concussion can be coufounded by the effects of exercise. Indeed, available data show that the brain of athletes is different from that of healthy individuals with a non-active lifestyle. As a result, sports concussions take place in a context where structural/functional plasticity has occurred prior to the concussive event. The sports concussion literature does not permit, at present, to separate the effects of intense and repeated physical activity, and the abrupt removal from such activities, from those of concussion on brain structure and function.

Glutamate and GABA concentrations following mild traumatic brain injury: a pilot study

Animal models of mild traumatic brain injury (mTBI) suggest that metabolic changes in the brain occur immediately after a mechanical injury to the head. Proton magnetic resonance spectroscopy (¹H-MRS) can be used to determine relative concentrations of metabolites in vivo in the human brain. The purpose of this study was to determine concentrations of glutamate and GABA in the brain acutely after mTBI and throughout 2 mo of recovery. Concentrations of glutamate and GABA were obtained using ¹H-MRS in nine individuals who had suffered an mTBI and nine control individuals in two brain regions of interest: the primary motor cortex (M1), and the dorsolateral prefrontal cortex (DLPFC), and at three different time points postinjury: 72 h, 2 wk, and 2 mo postinjury. There were no differences between groups in concentrations of glutamate or GABA, or the ratio of glutamate to GABA, in M1. In the DLPFC, glutamate concentration was lower in the mTBI group compared with controls at 72 h postinjury (d = 1.02), and GABA concentration was lower in the mTBI group at 72 h and 2 wk postinjury (d = 0.81 and d = 1.21, respectively). The ratio of glutamate to GABA in the DLPFC was higher in the mTBI group at 2 wk postinjury (d = 1.63). These results suggest that changes in glutamate and GABA concentrations in the brain may be region-specific and may depend on the amount of time that has elapsed postinjury. NEW & NOTEWORTHY To our knowledge, this is the first study to examine neurotransmitter concentrations in vivo at multiple time points throughout recovery from mild traumatic brain injury in humans.

Concussion May Increase the Risk of Subsequent Lower Extremity Musculoskeletal Injury in Collegiate Athletes

BACKGROUND

Laboratory-based studies on neuromuscular control after concussion and epidemiological studies suggest that concussion may increase the risk of subsequent musculoskeletal injury.

OBJECTIVE

The purpose of this study was to determine if athletes have an increased risk of lower extremity musculoskeletal injury after return to play from a concussion.

METHODS

Injury data were collected from 2006 to 2013 for men's football and for women's basketball, soccer and lacrosse at a National Collegiate Athletic Association Division I university. Ninety cases of in-season concussion in 73 athletes (52 male, 21 female) with return to play at least 30 days prior to the end of the season were identified. A period of up to 90 days of in-season competition following return to play was reviewed for time-loss injury. The same period was studied in up to two control athletes who had no concussion within the prior year and were matched for sport, starting status and position.

RESULTS

Lower extremity musculoskeletal injuries occurred at a higher rate in the concussed athletes (45/90 or 50 %) than in the non-concussed athletes (30/148 or 20 %; P < 0.01). The odds of sustaining a musculoskeletal injury were 3.39 times higher in the concussed athletes (95 % confidence interval 1.90-6.05; P < 0.01). Overall, the number of days lost because of injury was similar between concussed and non-concussed athletes (median 9 versus 15; P = 0.41).

CONCLUSIONS

The results of this study demonstrate a relationship between concussion and an increased risk of lower extremity musculoskeletal injury after return to play, and may have implications for current medical practice standards regarding evaluation and management of concussion injuries.

The Role of Physical Activity in Recovery From Concussion in Youth: A Neuroscience Perspective

BACKGROUND AND PURPOSE

Concussion is a major public health concern and one of the least understood neurological injuries. Children and youth are disproportionally affected by concussion, and once injured, take longer to recover. Current guidelines recommend a period of physical and cognitive rest with a gradual progressive return to activity. Although there is limited high-quality evidence (eg, randomized controlled trials) on the benefit of physical activity and exercise after concussion, most studies report a positive impact of exercise in facilitating recovery after concussion. In this article we characterize the complex and dynamic changes in the brain following concussion by reviewing recent results from neuroimaging studies and to inform physical activity participation guidelines for the management of a younger population (eg, 14-25 years of age) after concussion.

SUMMARY OF KEY POINTS

Novel imaging methods and tools are providing a picture of the changes in the structure and function of the brain following concussion. These emerging results will, in the future, assist in creating objective, evidence-based pathways for clinical decision-making. Until such time, physical therapists should be aware that current neuroimaging evidence supports participation in physical activity after an initial and brief period of rest, and consider how best to incorporate exercise into rehabilitation to enhance recovery following concussion.

RECOMMENDATIONS FOR CLINICAL PRACTICE

It is important that physical therapists understand the neurobiological impact of concussion injury and recovery, and be informed of the scientific rationale for the recommendations and guidelines for engagement in physical activity.Video Abstract available for more insights from the authors (see Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A205).

Neuromechanical Considerations for Postconcussion Musculoskeletal Injury Risk Management

Recent epidemiological studies have documented increased susceptibility to musculoskeletal injury after sport-related concussion, which raises questions about the adequacy of current clinical practices to ensure safe return to sport. A growing body of evidence derived from advanced neuroimaging and neurological assessment methods strongly suggests that mild traumatic brain injury has long-lasting adverse effects that persist beyond resolution of clinical symptoms. Plausible interrelationships among postconcussion changes in brain structure and function support the rationale for specific methods of clinical assessment and training to target the interaction of cognitive and motor function for reduction of musculoskeletal injury risk after concussion. The findings of preliminary clinical studies are presented to support suggested strategies for reduction of postconcussion musculoskeletal injury risk, and to identify novel approaches that we consider worthy areas for further research.

Osteoarthritis Prevalence in Retired National Football League Players With a History of Concussion and Lower Extremity Injury

CONTEXT

  Dynamic balance deficits have been described postconcussion, even after athletes return to play. Lower extremity (LE) musculoskeletal injury rates increase for up to 1 year after concussion, but the long-term musculoskeletal implications of concussion are unclear.

OBJECTIVE

  To (1) examine the association of concussion and LE injury histories with osteoarthritis (OA) prevalence in retired National Football League players and (2) examine the association of concussion and LE injury histories with OA prevalence in those ≤55 years of age.

DESIGN

  Case-control study.

SETTING

  Survey.

PATIENTS OR OTHER PARTICIPANTS

  We administered the Health Survey of Retired National Football League Players, which collects information about demographics, OA, LE injury, and concussion history.

MAIN OUTCOME MEASURE(S)

  Twelve discrete categories were created based on concussion and LE injury history, ranging from 0 concussions and 0 LE injuries (referent group) to 3+ concussions and 2+ LE injuries. Binomial regression analysis modeled lifetime OA prevalence. Covariates were body mass index, age at the time of the survey, and total years playing professional football.

RESULTS

  Complete data were available for 2696 participants. Lifetime OA prevalence was smallest in the referent group (21.1%) and largest in the 3+ concussion and 2+ LE group (50.6%; 2.5 times the referent; 95% confidence interval [CI] = 2.1, 3.1). Participants in all concussion groups (1, 2, 3+) who reported a history of 0 LE injuries had a greater OA prevalence than the referent group. When participants were stratified by age, the ≤55 years of age, 3+ concussions, and 2+ LE injuries group prevalence ratio (3.6; 95% CI = 2.7, 5.2) was larger than that of the >55 years of age, 3+ concussions, and 2+ LE injuries group (1.8; 95% CI = 1.3, 2.4) compared with the respective referent groups.

CONCLUSIONS

  Concussion with or without a history of LE injury may be an important moderator of OA. Future researchers should seek to better understand the mechanisms that influence the association among concussion, LE injury, and OA.

Evidence for Acute Electrophysiological and Cognitive Changes Following Routine Soccer Heading

Introduction

There is growing concern around the effects of concussion and sub-concussive impacts in sport. Routine game-play in soccer involves intentional and repeated head impacts through ball heading. Although heading is frequently cited as a risk to brain health, little data exist regarding the consequences of this activity. This study aims to assess the immediate outcomes of routine football heading using direct and sensitive measures of brain function.

Methods

Nineteen amateur football players (5 females; age 22 ± 3 y) headed machine-projected soccer balls at standardized speeds, modelling routine soccer practice. The primary outcome measure of corticomotor inhibition measured using transcranial magnetic stimulation, was assessed prior to heading and repeated immediately, 24 h, 48 h and 2 weeks post-heading. Secondary outcome measures were cortical excitability, postural control, and cognitive function.

Results

Immediately following heading an increase in corticomotor inhibition was detected; further to these electrophysiological alterations, measurable reduction memory function were also found. These acute changes appear transient, with values normalizing 24 h post-heading.

Discussion

Sub-concussive head impacts routine in soccer heading are associated with immediate, measurable electrophysiological and cognitive impairments. Although these changes in brain function were transient, these effects may signal direct consequences of routine soccer heading on (long-term) brain health which requires further study.

•

Standard soccer heading results in immediate and measurable alterations in brain function.

•

Changes in short and long term memory function and corticomotor inhibition are detectable immediately after soccer heading.

•

These changes in brain function after just a single session of heading appear transient.

•

These data provide direct evidence of immediate brain functional impairment associated with soccer heading.

Questions have been raised over whether soccer heading might have an effect on a player's brain, with particular worry over the proposed link between brain injury and increased risk of dementia. However, until now there have been no studies of the immediate effects of heading in soccer directly on brain function. This study found that just a single session of heading practice resulted in temporary impairment of short and long term memory function and in electrophysiological function of the brain. Whether these effects remain temporary after repeated soccer heading exposure and their long-term consequences on brain health must now be investigated.

Decreased high-frequency center-of-pressure complexity in recently concussed asymptomatic athletes

Two experiments compared multiple methods of estimating postural stability entropy to address: 1) if postural complexity differences exist between concussed and healthy athletes immediately following return-to-play; 2) which methods best detect such differences; and 3) what is an appropriate interpretation of such differences. First, center of pressure (COP) data were collected from six concussed athletes over the six weeks immediately following their concussion and from 24 healthy athletes. Second, 25 healthy non-athletes performed four quiet standing tasks: normal, co-contracting their lower extremity muscles, performing a cognitive arithmetic task, and voluntarily manipulating their sway. Postural complexity was calculated using approximate, sample, multi-variate sample, and multi-variate composite multi-scale (MV-CompMSE) entropy methods for both high-pass filtered and low-pass filtered COP data. MV-CompMSE of the high-pass filtered COP signal identified the most consistent differences between groups, with concussed athletes exhibiting less complexity over the high frequency COP time-series. Among healthy non-athletes, high-pass filtered MV-CompMSE increased only in the co-contraction condition, suggesting the decrease in high frequency MV-CompMSE found in concussed athletes may be due to more relaxed muscles or less complex muscle contractions. This decrease in entropy may associate with reported increases in intra-cortical inhibition. Furthermore, a single-case study suggested high frequency MV-CompMSE may be a useful clinical tool for concussion management.

Acute Lower Extremity Injury Rates Increase after Concussion in College Athletes

Dynamic postural control deficits and disrupted cortical pathways have been reported to persist beyond an athlete's return to activity after concussion, potentially increasing the risk of acute lower extremity musculoskeletal injury.

PURPOSE

This study aimed to investigate acute lower extremity musculoskeletal injury rates before and after concussion in athletes with concussion and their matched control.

METHODS

College athletes with concussion (n = 44; age, 20.0 ± 1.2 yr) were physician-diagnosed. Nonconcussed college athletes (n = 58; age, 20.5 ± 1.3 yr) were matched to individuals with concussion. Acute lower extremity musculoskeletal injury data were collected for 2 yr (±1 yr of the diagnosed concussion) using electronic medical records. Control participants' 2-yr window for exposure and musculoskeletal injury data were anchored to their match's concussion injury date. Pre- and postconcussion musculoskeletal injury rates were calculated for 90-, 180-, and 365-d periods for both study cohorts. Risk ratios were calculated to determine differences within and between groups for all periods.

RESULTS

Within 1 yr after concussion, the group with concussion was 1.97 (95% confidence interval (CI), 1.19-3.28; P = 0.01) times more likely to have experienced an acute lower extremity musculoskeletal injury after concussion than before concussion and 1.64 times (95% CI, 1.07-2.51; P = 0.02) more likely to have experienced an acute lower extremity musculoskeletal injury after concussion than their matched nonconcussed cohort over the same period. Up to 180 d after concussion, the group with concussion was 2.02 (95% CI, 1.08-3.78; P = 0.02) times more likely to have experienced an acute lower extremity musculoskeletal injury after concussion than before concussion.

CONCLUSIONS

Previous literature has identified dynamic postural control deficits along with increased motor evoked potential latency and decreased amplitude after concussion, suggesting that the brain may be unable to effectively coordinate movement. Our findings underscore the need to explore functional movement and dynamic postural control assessments in postconcussion injury assessment protocols.

Concussion Frequency Associates with Musculoskeletal Injury in Retired NFL Players

OBJECTIVE

Concussion is commonly associated with immediate and persistent alterations in motor function affecting postural control and gait. Patients with lower extremity joint injury have demonstrated functional alterations in the cerebral cortex, suggesting that musculoskeletal injury may be linked to alterations in brain function. Therefore, we examined the associations between concussion frequency and lower extremity musculoskeletal injury sustained during professional careers of National Football League (NFL) players in a cross-sectional study.

METHODS

An inclusive health history survey was mailed to 3647 NFL players who retired during 1930-2001. Respondents reported total concussion frequency (zero, one, two, or three or more) and presence (yes/no) of specific knee and ankle musculoskeletal injury during their NFL career. Separate logistic regression models were used to estimate associations between concussion frequency and each musculoskeletal injury type, adjusting for number of years played in the NFL, body mass index while playing in the NFL, and playing position.

RESULTS

Data from 2429 players (66.6% response rate) were available for analysis. Nearly 61% reported experiencing a concussion while competing in the NFL. Meniscal tear was the most commonly reported musculoskeletal injury (32%). Compared with NFL players who did not sustain a concussion, retired NFL players with one, two, or three or more concussions had between 18% and 63%, 15% and 126%, and 73% and 165% higher odds of reporting various musculoskeletal injuries, respectively.

CONCLUSIONS

A history of concussions was associated with a history of musculoskeletal injuries during NFL careers. These data suggest that a higher number of concussions is linked with higher odds of reporting a musculoskeletal injury.

Acute and longitudinal changes in motor cortex function following mild traumatic brain injury

PRIMARY OBJECTIVE

To evaluate excitability and inhibition of the motor cortex acutely and longitudinally following mild traumatic brain injury (mTBI).

RESEARCH DESIGN

A longitudinal paired case-control design was used to examine cortical excitability and inhibition in 15 adults who had sustained an mTBI (mean age = 20.8 ± 1.2 years) and 15 matched control participants (mean age = 21.1 ± 1.3 years).

METHODS AND PROCEDURES

Participants visited the lab within 72 hours of injury and again at 1, 2, 4 and 8 weeks post-injury. During each visit, transcranial magnetic stimulation was used to examine resting motor threshold (RMT), motor evoked potential peak-to-peak amplitude (MEPamp) and cortical silent period (CSP) duration of the first dorsal interosseous muscle.

MAIN OUTCOMES AND RESULTS

There were no differences between groups in RMT (p = 0.10) or MEPamp (p = 0.22) at 72 hours post-injury or across the 2-month testing period (p ≥ 0.68), indicating similar cortical excitability. However, the CSP duration was higher in individuals with mTBI, indicating greater intra-cortical inhibition compared with the control group at 72 hours post-injury (p = 0.03) and throughout the 2 months of recovery (p = 0.009).

CONCLUSIONS

mTBI appeared to have little effect on cortical excitability, but an acute and long-lasting effect on intra-cortical inhibition.

Cortical hypoexcitability persists beyond the symptomatic phase of a concussion

PRIMARY OBJECTIVE

The purpose of this research was to assess cortical excitability, voluntary activation of muscle and force sensation beyond the initial highly symptomatic period post-concussion (1-4 weeks post-injury). It was hypothesized that reduced excitability of the motor cortex may impair muscle activation and alter perceptions of force and effort.

RESEARCH DESIGN

Eight concussed varsity football players were age- and position-matched with eight healthy teammates to control for training and body size. Healthy controls had not suffered a concussion in the previous 12 months.

METHODS AND PROCEDURES

Paired-pulse transcranial magnetic stimulation was used to assess cortical excitability, voluntary activation was calculated using cortical twitch interpolation technique and sense of force was determined using constant-force sensation contractions.

MAIN OUTCOMES AND RESULTS

The concussed group had lower intra-cortical facilitation (p = 0.036), lower maximal voluntary muscle activation (p = 0.038) and greater perceptions of force (p < 0.05), likely due to compensatory increases in upstream drive, than their healthy matched teammates.

CONCLUSIONS

Taken together, these findings suggest a state of hypoexcitability that persists beyond the immediate acute phase of a concussion and may result in neuromuscular impairments that would call to question the athlete's readiness to return to sport.

The persistent influence of concussive injuries on cognitive control and neuroelectric function

CONTEXT

Increasing attention is being paid to the deleterious effects of sport-related concussion on cognitive and brain health.

OBJECTIVE

To evaluate the influence of concussion incurred during early life on the cognitive control and neuroelectric function of young adults.

DESIGN

Cross-sectional study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Forty young adults were separated into groups according to concussive history (0 or 1+). Participants incurred all injuries during sport and recreation before the age of 18 years and were an average of 7.1 ± 4.0 years from injury at the time of the study.

INTERVENTION(S)

All participants completed a 3-stimulus oddball task, a numeric switch task, and a modified flanker task during which event-related potentials and behavioral measures were collected.

MAIN OUTCOME MEASURE(S)

Reaction time, response accuracy, and electroencephalographic activity.

RESULTS

Compared with control participants, the concussion group exhibited decreased P3 amplitude during target detection within the oddball task and during the heterogeneous condition of the switch task. The concussion group also displayed increased N2 amplitude during the heterogeneous version of the switch task. Concussion history was associated with response accuracy during the flanker task.

CONCLUSIONS

People with a history of concussion may demonstrate persistent decrements in neurocognitive function, as evidenced by decreased response accuracy, deficits in the allocation of attentional resources, and increased stimulus-response conflict during tasks requiring variable amounts of cognitive control. Neuroelectric measures of cognitive control may be uniquely sensitive to the persistent and selective decrements of concussion.

Concussions: What a neurosurgeon should know about current scientific evidence and management strategies

BACKGROUND

There has been a tremendous amount of interest focused on the topic of concussions over the past few decades. Neurosurgeons are frequently consulted to manage patients with mild traumatic brain injuries (mTBI) that have radiographic evidence of cerebral injury. These injuries share significant overlap with concussions, injuries that typically do not reveal radiographic evidence of structural injury, in the realms of epidemiology, pathophysiology, outcomes, and management. Further, neurosurgeons often manage patients with extracranial injuries that have concomitant concussions. In these cases, neurosurgeons are often the only "concussion experts" that patients encounter.

RESULTS

The literature has been reviewed and data have been synthesized on the topic including sections on historical background, epidemiology, pathophysiology, diagnostic advances, clinical sequelae, and treatment suggestions, with neurosurgeons as the intended target audience.

CONCLUSIONS

Neurosurgeons should have a fundamental knowledge of the scientific evidence that has developed regarding concussions and be prepared to guide patients with treatment plans.