Sports medicine

Tissue vulnerability is increased following repetitive mild traumatic brain injury in the rat

Authors: Huang L, Coats JS, Mohd-Yusof A, Yin Y, Assaad S, Muellner MJ, Kamper JE, Hartman RE, Dulcich M, Donovan VM, Oyoyo U, Obenaus A.

Repetitive mild traumatic brain injury (rmTBI) is an important medical concern for active sports and military personnel. Multiple mild injuries may exacerbate tissue damage resulting in cumulative brain injury and poor functional recovery. In the present study, we investigated the time course of brain vulnerability to rmTBI in a rat model of mild cortical controlled impact. An initial mild injury was followed by a second injury unilaterally at an interval of 1, 3, or 7 days. RmTBI animals were compared to single mTBI and sham treated animals. Neuropathology was assessed using multi-modal magnetic resonance imaging (MRI), followed by ex vivo tissue immunohistochemistry. Neurological and behavioral outcomes were evaluated in a subset of animals receiving rmTBI 3 days apart and shams. RmTBI 1 or 3 days apart but not 7 days apart revealed significantly exacerbated MRI-definable lesion volumes compared to single mTBI and shams. Increases in cortical tissue damage, extravascular iron and glial activation assessed by histology/immunohistochemistry correlated with in vivo MRI findings where shorter intervals (1 or 3 days apart) resulted in increased tissue pathology. There were no neurological deficits associated with rmTBI 3 day animals. At 1 mo post-injury, animals with rmTBI 3 days apart showed reduced exploratory behaviors and subtle spatial learning memory impairments were observed. Collectively, our findings suggest that the mildly-impacted brain is more vulnerable to repetitive injury when delivered within 3 days following initial mTBI.

Concussion in athletics: ongoing clinical and brain imaging research controversies

Authors: Slobounov S, Gay M, Johnson B, Zhang K.

Concussion, the most common form of traumatic brain injury, proves to be increasingly complex and not mild in nature as its synonymous term mild traumatic brain injury (mTBI) would imply. Despite the increasing occurrence and prevalence of mTBI there is no universally accepted definition and conventional brain imaging techniques lack the sensitivity to detect subtle changes it causes. Moreover, clinical management of sports induced mild traumatic brain injury has not changed much over the past decade. Advances in neuroimaging that include electroencephalography (EEG), functional magnetic resonance imaging (fMRI), resting-state functional connectivity, diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS) offer promise in aiding research into understanding the complexities and nuances of mTBI which may ultimately influence clinical management of the condition. In this paper the authors review the major findings from these advanced neuroimaging methods along with current controversy within this field of research. As mTBI is frequently associated with youth and sports injury this review focuses on sports-related mTBI in the younger population.

Mild traumatic brain injury: lessons learned from clinical, sports, and combat concussions

Authors: Kelly JC, Amerson EH, Barth JT.

Over the past forty years, a tremendous amount of information has been gained on the mechanisms and consequences of mild traumatic brain injuries. Using sports as a laboratory to study this phenomenon, a natural recovery curve emerged, along with standards for managing concussions and returning athletes back to play. Although advances have been made in this area, investigation into recovery and return to play continues. With the increase in combat-related traumatic brain injuries in the military setting, lessons learned from sports concussion research are being applied by the Department of Defense to the assessment of blast concussions and return to duty decision making. Concussion management and treatment for military personnel can be complicated by additional combat related stressors not present in the civilian environment. Cognitive behavioral therapy is one of the interventions that has been successful in treating symptoms of postconcussion syndrome. While we are beginning to have an understanding of the impact of multiple concussions and subconcussive blows in the sports world, much is still unknown about the impact of multiple blast injuries.

Making Soccer Safer for the Brain: DTI-defined Exposure Thresholds for White Matter Injury Due to Soccer Heading

Authors: Molly Zimmerman PhD., Richard Lipton, Walter Stewart PhD., Edwin Gulko MD., Michael Lipton MD, PhD., Craig Branch PhD

PURPOSE: Heading the soccer ball may represent a form of repetitive mild trauma and may be associated with cognitive impairment. Because abnormally low white matter FA has been associated with cognitive impairment in patients with TBI, we hypothesized that a threshold level exists for heading exposure above which evidence of white matter injury is detectable.

METHOD AND MATERIALS: 32 amateur soccer players were recruited. Heading exposure was assessed with a standardized questionnaire and DTI was performed. Regions of Interest (ROI) were determined using a voxelwise t-test comparing FA between subjects with heading frequency ≥1,320/year with those <1,320/year. Based on our threshold hypothesis, we assumed an S or inverse S shape, nonlinear regression model based on Inverse Logit functions with four parameters: (1) associational direction and scale factor (β1), (2) baseline (β2) in FA measures for players with low frequency of headings, (3) departure position (β3) in heading-exposure scales from baseline and (4) slope (β4) of the curve. These parameters were estimated utilizing a stochastic search algorithm, simulated annealing (Kirkpatrick et al., 1983).
  
RESULTS: 5 ROIs were identified in temporooccipital white matter and one frontal white matter. Nonlinear regression reduced mean square error by 14% to 93% across all ROIs when compared to linear regression fits. All curve fitting detected an inverse S shape, indicating that FA decreases as exposure to heading increases. Estimates of departure position (β3) in heading-exposure scales were around 1500 in 4 temporooccipital ROIs 1000 in the 5th ROI. β3 was 1300 in the frontal ROI.

CONCLUSION: Greater heading frequency is associated with low FA. Exceeding a threshold for heading frequency (1000-1500) may result in brain abnormalities similar to those seen in TBI. Investigation of the relationship of the imaging abnormalities to cognitive performance is needed.

CLINICAL RELEVANCE/APPLICATION: Soccer heading is associated with DTI findings similar to TBI. The exposure threshold we identify suggests public health interventions to minimize excess exposure and, thereby, the adverse outcomes.

Imaging modalities in mild traumatic brain injury and sports concussion

Authors: Gonzalez PG, Walker MT.

Mild traumatic brain injury is a significant public health issue that has been gaining considerable attention over the past few years. After injury, a large percentage of patients experience postconcussive symptoms that affect work and school performance and that carry significant medicolegal implications. Conventional imaging modalities (computed tomography and magnetic resonance imaging) are insensitive to microstructural changes and underestimate the degree of diffuse axonal injury and metabolic changes. Newer imaging techniques have attempted to better diagnose and characterize diffuse axonal injury and the metabolic and functional aspects of traumatic brain injury. The following review article summarizes the currently available imaging studies and describes the novel and more investigational techniques available for mild traumatic brain injury. A suggested algorithm is offered.

Long-term Consequences of Repetitive Brain Trauma: Chronic Traumatic Encephalopathy

Authors: Stern RA, Riley DO, Daneshvar DH, Nowinski CJ, Cantu RC, McKee AC.

Chronic traumatic encephalopathy (CTE) has been linked to participation in contact sports such as boxing and American football. CTE results in a progressive decline of memory and cognition, as well as depression, suicidal behavior, poor impulse control, aggressiveness, parkinsonism, and, eventually, dementia. In some individuals, it is associated with motor neuron disease, referred to as chronic traumatic encephalomyelopathy, which appears clinically similar to amyotrophic lateral sclerosis. Results of neuropathologic research has shown that CTE may be more common in former contact sports athletes than previously believed. It is believed that repetitive brain trauma, with or possibly without symptomatic concussion, is responsible for neurodegenerative changes highlighted by accumulations of hyperphosphorylated tau and TDP-43 proteins. Given the millions of youth, high school, collegiate, and professional athletes participating in contact sports that involve repetitive brain trauma, as well as military personnel exposed to repeated brain trauma from blast and other injuries in the military, CTE represents an important public health issue. Focused and intensive study of the risk factors and in vivo diagnosis of CTE will potentially allow for methods to prevent and treat these diseases. Research also will provide policy makers with the scientific knowledge to make appropriate guidelines regarding the prevention and treatment of brain trauma in all levels of athletic involvement as well as the military theater.

Pages

Subscribe to RSS - Sports medicine