Article, Sports Medicine

The sports medicine literature 2013

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American Journal of Emergency Medicine

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The sports medicine literature 2013

Monique Alworth, MD a,?, Michael C. Bond, MD a, William J. Brady, MD b

a Emergency Medical Services University of Maryland Medical Center, Baltimore, MD 21201, USA

b Department of Emergency Medicine University of Virginia School of Medicine, Charlottesville, VA 22908, USA

Closed head injuries

A. McCrory P, Meeuwisse WH, Aubry M, et al. Consensus statement on concussion in sportsthe 4th International Conference on Concussion in Sport held in Zurich, November 2012. Clin J Sport Med 2013;23(2):89-108

Concussion is one of the most widely discussed topics in sports medicine. The general public has an increasing awareness about closed head injuries and the devastating effects they can have on athletes. Some sports are changing the way the game is played–from adding protective equipment in women’s lacrosse to enforcing stricter rules against aggression in ice hockey. The Centers for Disease Control and Prevention (CDC) reports that emergency departments (ED) in the United States treat an estimated 173,285 sports- and recreation- related Traumatic brain injuries (TBIs) in children and adolescents (from birth to 19 years of age) every year [1]. During the past decade, ED visits for injuries, including concussions, increased by 60% [1]. There is no ideal diagnostic test for concussion that physicians can rely upon, making the diagnosis difficult. Furthermore, physicians often find it challenging to facilitate a safe return to play for athletes.

The consensus statement on sports concussion and Management issues is intended to be a guide for sports medicine and other clinicians who treat such patients; importantly, this statement is not an expression of standard of care, as noted by the authors. The consensus conference presented a non-government, non-advocacy panel of researchers in clinical medicine, sports medicine, neurosci- ence, athletic training, neuroimaging, and sports science. The goal was to give balanced, objective, and knowledgeable review of the topic–concussion in sport.

The consensus statement defines concussion as a complex pathophysiologic process that affects the brain and is induced by biomechanical forces. It is characterized by the following features [1]: caused by a direct blow to the head, or elsewhere on body, transmitting an “impulsive” force to the head; [2] evolving injury, typically resulting in the rapid onset of short-lived impairment of neurologic function, which resolves spontaneously over a number of minutes to hours; [3] acute clinical symptoms reflect a functional disturbance rather than a structural injury; [4] images obtained during the diagnostic process are normal; and recovery to normal function within 7 to 10 days (note that Recovery time can be longer in children and adolescents). The statement describes the signs and

* Corresponding author. University of Maryland Medical Center Emergency Medical Services Baltimore, MD 21201 United States.

E-mail address: [email protected] (M. Alworth).

symptoms of acute concussion, based on five clinical domains: somatic (headache), cognitive (feeling like fog) or emotional symptoms (lability), physical signs (LOC, amnesia), behavioral changes (irritability), cognitive impairment (slowed reaction times), and sleep disturbance (insomnia)–if any of these symptoms are present, concussion must be suspected.

The consensus recommendations for sideline assessment include initially considering cervical spine injury followed by an immediate full assessment by a health care provider. The athlete should be removed from practice or play and should, under no circumstances, return to play on the same day of injury. The Sport Concussion Assessment Tool, Version 3 (SCAT3), has been developed to guide the clinical assessment [2]. Standard orientation questions such as time, place, and person are unreliable compared with memory assessment. The group recommends serial monitoring for deterioration over the initial few hours following injury. The diagnosis is based on clinical judgment.

The ED evaluation should entail a focused and appropriate history and neurologic examination; assessment basic Cognitive function is considered. It should collect collateral information from bystanders, such as improvement or deterioration since the time of injury. The emergency physician will determine the need for imaging, which is most likely in patients with a suspected Skull fracture, focal neurologic deficit, worsening symptoms, or prolonged LOC; however, imaging is not required in all patients.

As stated above, the statement is clear that no athlete should return to play on the day of injury, but the optimal amount of rest needed for recovery varies by person, regardless of the level of training. Further research is needed to clarify this aspect of the Management strategy. Physical and cognitive rest is recommended until the acute symptoms resolve, especially within the first 24 to 48 hours. The athlete may return to play when he or she is symptom free and not taking any medications that could mask or modify symptoms. Implementation of a graded return-to-play program is recommended, starting with minimal activity and gradually increasing intensity every 24 hours so long as the athlete remains asymptomatic.

Several factors modify the management approach to concussion. Males experience concussion more often than females (as much as 70% male gender occurrence). Data suggest that Female gender might be a risk factor for injury or influence injury severity [3-5]. However, evidence regarding gender remains inconclusive. The duration of altered LOC (eg, greater than 1 minute) is associated with the rate of cognitive deficits but is not noted as a measure of injury severity [6,7]. Posttraumatic retrograde amnesia is also poorly reflective of injury severity [8,9]. The duration of symptoms is probably more important than the duration of amnesia [10,11].

0735-6757/(C) 2015

Cervical spine injuries“>Age also plays a role in concussion management. Children younger than 12 years of age might need longer periods of cognitive and physical rest, as symptoms often last longer in this population [12]. The Consensus guidelines apply to athletes over 13 years old. A more developmentally sensitive CHILD-SCAT3 was developed for children between the ages of 5 and 12 [13]. A more conservative return-to-play approach is recommended for younger athletes.

Over the next decade, if the trend continues, emergency care providers can expect to see triple the number of sport-related concussions. At disposition, patients and parents will need counseling regarding return to play and what to expect over the next several days to weeks.

B. Harris AW, Voaklander DC, Jones CA, Rowe BH. Time-to- subsequent head injury from sports and recreation activities. Clin J Sport Med 2012;22:91-97

This article explores the issue of repeat concussion-type injury – i.e., a recurrent concussion after the initial concussive head injury. This topic is important in that data suggest that athletes with an initial concussion have a greater tendency for repeat injury [14] as well as diffuse cerebral edema [15,16], cognitive slowing, early-onset Alzhei- mer’s disease [17], and chronic traumatic encephalopathy [18].

Harris and colleagues conducted a retrospective cross-sectional study in which they examined data from patients with head injuries sustained during sports and recreation activities, who were treated at five hospitals in Alberta, Canada between 1997 and 2008. The goal of the study was to determine the risk of presenting to an ED with a subsequent sports-related head injury and to determine the duration between the injuries. ED charts and administrative health databases were reviewed for sports-related injuries. The patients represented a wide range of ages (from 4 to 34 years); 72.7% of patients were male. Seven hundred forty-six patients presented with an initial sports- related head injury. Two hundred (26.8%) presented with a second head injury and 13 (1.7%) with a third injury. The median time to second injury was 8.7 years, and the median time to a third injury was

4.8 years. Although the length of time between injuries was longer than reported from most other studies, it is important to recognize that the interval shortened as more head injuries occurred. Using Cox regression analysis, Harris and colleagues determined that the hazard ratio for sustaining a second sports-related head injury was 2.62 (95% CI, 2.233.07) and that the risk for sustaining a third head injury rose to 5.94 (95% CI, 3.43-10.29).

A secondary analysis using a logistic regression model showed that

sports involving animals, such as rodeo and horseback riding, had a higher odds ratio for head injury (3.54; 95% CI, 2.84-4.40). The next four sports activities with high odds ratios for head injury were rugby, riding all-terrain or off-road vehicles, hockey, and cycling, in that order, from greatest to least. The least likely sport to be associated with head injury was basketball, with an odds ratio of 0.38 (95% CI, 0.31-0.46).

Certainly, the findings are influenced by confounders such as type

of sport, level of participation, medical co-morbidities, methods of training, season duration, and gender. The analysis obviously did not include data from people with mild head injuries who did not seek evaluation in the ED. Because of the retrospective nature of this study, it would have been difficult to determine if any of the 746 patients had experienced mild head injury prior to their Subsequent ED visits. This type of unreported injury could have played a role in patients’ recovery.

Athletes who sustain multiple head trauma take longer to recover from repeat injury and usually experience more symptoms [19]. The findings of this study suggest that individuals with repeat injuries, especially younger patients, might need longer recovery times and greater rest periods than patients who have sustained their first head injury. In addition, the time interval between episodes of head injury tends to decrease as more traumatic incidents occur [20].

Cervical spine injuries

A. Decoster LC, Burns MF, Swartz EE, et al. Maintaining neutral sagittal cervical alignment after football helmet removal during emergency spine injury management. Spine 2012;37(8):654-659

The NCAA Sports Medicine Handbook [21] provides guidelines for safe helmet removal during the assessment of an athlete suspected of having a Spinal injury. The NCAA’s current recommendations are to obtain skull and spine radiographs with the helmet in place, before attempting equipment removal. This approach, however, does not address the reality of resuscitation and neutral cervical spine positioning; in fact, with a helmet in place, it is extremely difficult for emergency physicians to perform endotracheal intubation and to avoid undesired movement of the cervical spine. If emergent and radiographs are unable to be obtained, the recommendations suggest facemask removal to facilitate airway access, followed by simulta- neous helmet and shoulder pad removal [22,23].

Decoster and colleagues asked if placing padding under the occiput after removing the helmet, yet before shoulder pad removal, can maintain neutral sagittal cervical spine alignment. They evaluated 20 male volunteers (mean age, 23.6 years) who were wearing football helmets. To be eligible to participate in this study, the subjects could not have a history of cervical spine injury (instability, fractures, dislocation, facet pathology, disc herniation), thyroid pathology, or neuropathy; be undergoing radiation therapy; or have a current major systemic illness.

All of the volunteers were fitted by an athletic trainer with Schutt helmets without chin-straps and with Riddell shoulder pads, parts of which had been removed to allow radiographs to be obtained. The authors explained that the shoulder pad changes did not affect the thickness of the posterior aspect of pads and maintained the pad-helmet relationship. Cotton towels typically used by Prehospital care providers for splinting were used as occipital padding. The towels were piled high enough to match the thickness of the helmet. The shoulder pads were left in place. Three investigators were involved in the preparation of the volunteers for radiography: one provided in-line stabilization, one removed the helmet, and one placed towels under the volunteer’s head. Three lateral Cervical spine radiographs were obtained with each volunteer lying supine: an initial radiograph with helmet and pads, a radiograph taken 20 minutes after towel placement, and a radiograph taken 20 minutes after the towels were removed.

As expected, the study found statistically significant differences in cervical lordosis between the helmeted position and the no-towel position as well as between the towel and no-towel conditions. However, the positions with a helmet and occipital towels were not significantly different, suggesting that towel support is adequate in maintaining alignment. The investigators used the same brand and model of equipment on all subjects; in real-world medical practice, different brands might create different spatial relationships, limiting the study’s external validity.

Although this study evaluated only sagittal alignment, it validates an option to helmet and shoulder pad removal when cervical spine injury is considered a possibility. Future studies should evaluate the occipital towel method as it applies to the general population in acute trauma as well as in coronal planes.

Intubation updates

A. Delaney JS, Al-Kashmiri A, Baylis PJ, et al. The effect of laryngoscope handle size on possible endotracheal intubation success in university football, ice hockey and Soccer players. Clin J Sports Med 2012;22(4):341-348

Helmeted, injured athletes pose a formidable challenge for the emergency medicine clinician. The need to secure a tenuous airway

while maintaining adequate cervical spinal alignment with the constraints of sports equipment such as a helmet and shoulder pads creates a complicated clinical scenario. The limited space between the anterior chest wall and the mandible makes endotracheal intubation difficult.

In a prospective, crossover study conducted at a Canadian sports

medicine clinic, Delaney and colleagues evaluated the success rate of attempts to intubate athletes wearing protective equipment. In-line Cervical immobilization was maintained, and laryngoscope handles of different sizes were employed. The facemasks were removed and the helmets and shoulder/chest padding was left in place. The study compared the success rates associated with the use of short and long laryngoscopy handles.

The study population consisted of 146 healthy volunteer athletes: 62 varsity football players (all male), 45 varsity ice hockey players (26 males, 19 females), and 39 varsity soccer players (20 males, 19 females). Exclusion criteria were a head or neck injury that precluded participation on a team, recent or current symptoms indicative of upper or lower respiratory tract infection (ie, fever, sore throat, shortness of breath, rhinorrhea, cough, increased sputum production), active oral or labial viral lesions, or consuming a meal within the preceding 120 minutes.

The investigators assessed each volunteer’s airway by assigning a Mallampati score, evaluating oral opening size, measuring the hyomental distance, performing the upper lip test (ability to place lower teeth over upper lip), and noting the presence of a beard or mustache, overbite, or false teeth. They used two laryngoscope handles: the Heine standard handle (152 mm long) and the Welch Allyn laryngoscope (108 mm long), each with a 4-0 Macintosh blade (160 mm long).

The posterior pharynx was anesthetized with topical lidocaine spray. Three sports medicine physicians (one trained in Family Medicine and two in emergency medicine) with a range of experience (2 to 10 years) evaluated the ease of intubation for each participant. The physicians used a grading system: 0, no pass; 1, difficult pass; 2, fairly easy pass; and 3, very easy pass.

Intubation was significantly more successful with the short- handled laryngoscope than with the long-handled instrument. There were 6 failed attempts with the short-handled laryngoscope versus 49 with the long-handled device. The most common reason for intubation difficulty was interference with the base of the laryngo- scope handle by the anterior chest or shoulder pads.

The athletes were awake during this study, and the physicians used the same size blade on each player, which is not ideal. The subjective scale used by these three investigators has limited external validity. Further, helmet and pad brand variability could have played a role in the study’s results. The authors acknowledged those weaknesses but also noted that emergency medicine physicians must be able to navigate endotracheal Intubation complications in athletes wearing protective gear. The study supports the use of a short-handled laryngoscope to improve intubation success rates.

Cardiovascular updates

A. Enright K, Turner C, Roberts P, et al. Primary cardiac arrest following sport or exertion in children presenting to an emergency department. Ped Emerg Care 2012;28(4):336-339

Recent changes in the American Heart Association’s guidelines for cardiopulmonary resuscitation (CPR) emphasize that the goal in responding to cardiac arrest is immediate chest compressions and Early defibrillation. Sudden cardiac death in children continues to be an area of research. The sudden cardiac death of a young athlete is an uncommon and tragic event.

In this prospective observational study, Enright and associates assessed out-of-hospital primary cardiac arrest in the pediatric

population and sought to determine whether survival is influenced by specific resuscitative interventions. The investigators reviewed cases of pediatric sudden cardiac death presenting to a tertiary pediatric ED (with 50,000 visits per year) in Sydney, Australia. The deaths occurred during a sports activity or other exertion between 2005 and 2010.

The study involved the records of nine children, 7 of whom were male, with a mean age of 10.7+-4.2 years. They had been involved in either running, football, swimming, rugby, or a charity walk at the time of their cardiac arrest. Six of the nine patients (66.6%) were discharged from the hospital and had a full Neurologic recovery. Two patients died in the ED and one died in the intensive care unit. All survivors had either ventricular fibrillation or tachycardia and received 5 minutes of uninterrupted chest compressions that were started within 2 minutes after the arrest. For the survivors, prehospital care personnel arrived within 10 minutes, cardioverted the patients to normal sinus rhythm, and delivered them to the ED within 30 minutes after the arrest. The survivors’ discharge diagnoses included commo- tio cordis, catecholaminergic Polymorphic ventricular tachycardia (CPVT; three patients), myocarditis, and Hypertrophic cardiomyopathy.

One of the patients who did not survive was not recognized to be in cardiac arrest at first, so CPR was delayed, starting 5 minutes after the initial event. That patient was in asystole on arrival at the ED. For a second non-survivor patient, CPR was initiated early after arrest but defibrillation was delayed 14 minutes. This patient was also in asystole on arrival at the ED. The third non-surviving patient had CPR started early after arrest, had defibrillation at 11 minutes, and had pulseless electrical activity on arrival at the ED. The autopsy reports listed the causes of death as long QT syndrome, myocarditis, and hypertrophic cardiomyopathy, respectively, in the non-survivors.

One survivor received epinephrine during the prehospital phase of care and had a longer cardiac arrest. This patient was later admitted to the ICU with Recurrent episodes of ventricular tachycardia, which was eventually controlled with ?-blockers. It is interesting that three of the survivors presented with CPVT. Had they been given epinephrine, the outcome might have been worse, because of the catecholamine surge. Early bystander intervention with CPR and early defibrillation is essential, as evidenced by the results of this study. These findings highlight the importance of automated external defibrillators (AEDs)–most patients present with a shockable rhythm. Patients in the ED should receive early, adequate chest compressions and early defibrillation. The role of epinephrine in the resuscitation of athletes in cardiac arrest remains controversial and requires more research

before definitive recommendations can be made.

B. Halkin A, Steinvil A, Rosso R, et al. Preventing sudden death of athletes with electrocardiographic screening: what is the absolute benefit and how much will it cost? J Am Coll Cardiol 2012;60(22):2271-2276

Following a 2005 Italian study that demonstrated the benefits of electrocardiographic screening in athletes, the European Society of Cardiology mandated this screening for all competitive athletes prior to participation in their sport. In the United States, the American Heart Association makes no such recommendation. To date, no comprehen- sive studies have examined the cost-benefit ratio of mandatory electrocardiographic screening of athletes in the United States. The authors sought to explore this issue by using a cost-projection model, based on the results of the study by Corrada and colleagues [24]. They reported a 79% relative risk reduction in the incidence of sudden cardiac death among high school and college athletes following the implementation of an Italian law mandating electrocardiographic screening. The study followed athletes over a 20-year period and tracked cardiac events. Mandatory electrocardiographic screening was implemented in Italy during the study period.

Halkin et al estimated the national annual expenditure related to mandatory electrocardiographic screening of competitive Young athletes in the United States as well as the cost of saving a single athlete’s life. First, they extrapolated the Italian data and applied the results to a similar population in the United States. Using data from the National Collegiate Athletic Association and the National Feder- ation of State High School Associations, the authors estimated the number of young athletes who would require electrocardiographic screening over two decades. They calculated the type, number, and costs of tests that would be performed in this population, including secondary tests driven by abnormal findings (e.g., Holter monitoring, echocardiography, cardiac magnetic resonance imaging [MRI], and cardiac catheterization). Using these data, they estimated the number of lives that would be saved by electrocardiographic screening.

The investigators estimated that a 2-decade electrocardiographic screening program involving all registered competitive high school and college athletes in the United States would cost between $51 and

$69 billion ($2.5-$3.4 billion per year). The number of lives that could be saved annually by screening would increase from 22 after 1 year to 469 in the 20th year. An estimated 4,813 lives could be saved during 20 years of screening.

These authors, constituting an American Heart Association expert panel, estimated that a preventive program consisting of widespread CPR training, effective communication systems within campuses, and AEDs operated by lay rescuers would result in a cost-per-life-saved of

$1.5 to $3.3 million. These preventive efforts, combined with mandatory electrocardiographic screening, could cost the United States approximately $4 billion a year.

Emergency physicians are at the diagnostic forefront when disease turns deadly. We are also frequently responsible for predicting outcomes. It is critical for emergency care providers to be aware of the benefit and cost implications of studies that we order. ECGs are often routine studies in the ED, but they can generate a landslide of additional testing that might not affect mortality or morbidity rates. When applied to an entire population of athletes as a mandate, the costs of electrocardiographic screening could have profound implica- tions on society.

C. Tanguturi VK, Noseworthy PA, Newton-Cheh C, Baggish AL. The electrocardiographic early repolarization pattern in athletes: normal variant or sudden death risk factor? Sports Med 2012;42(5):359-366

The ECG is used frequently in the athlete, whether it be employed in a screening fashion prior to involvement or in the evaluation of a symptomatic event. Abnormal electrocardiographic findings in ath- letes are undergoing extensive study. Differentiating cardiovascular disease from benign variants is a complex undertaking. Data suggest that patients who have what were once thought to be benign electrocardiographic findings, such as early repolarization pattern (ERP), are at greater risk for sudden cardiac death.

The review article by Tanguturi and colleagues addresses ERP as it applies to athletes and asks if athletes are at increased risk for sudden cardiac death. The authors define ERP as follows: 1) the QRS-ST junction (J point) deviates from baseline by >= 0.1 mV in at least two contiguous leads, 2) the morphology of the J point is either slurred or notched, and 3) the ST segment from the J point to the T wave is ascending, descending, or horizontal. In 1951, Grant et al proposed that ERP was caused by diffuse repolarization vectors that occur early after depolarization [25].

ERP is found in 1% to 5% of the general population and is most frequently seen in the precordial or inferior leads. It has a known association with the African-American race, male gender, lower heart rate (often seen in athletes), and increased QRS voltage [26]. The incidence of sudden cardiac death is difficult to estimate, because data reports on the subject are limited and most are retrospective in nature. Although Tanguturi and associates found no data that

specifically address ERP in athletes and sudden cardiac death, evidence of a relationship is suggested by studies involving the general population. For athletes, the risk for sudden death likely depends on the level of training and age and the incidence is around 4 per 100,000 athletes [24].

ERP is actually a dynamic phenomenon and is a direct result of intense physical activity. ERP rates increase from 37.2% to 52.7% following exercise training [26].

Several conclusions can be based on this review. The first is that there is a lack of data showing a higher incidence of sudden cardiac death among athletes despite them having higher rates of ERP. Second, athletes do not seem to have a higher incidence of sudden cardiac death than the general population, even though they have a higher rate of ERP. Third, ERP is dynamic in athletes and not a fixed electrophysiologic defect [26]; it is thus dependent on training and not necessarily suggestive of cardiovascular disease. And, fourth, an ascending ST segment, commonly found in athletes, is not associated with arrhythmic deaths in the general population; sudden death is related to a downsloping segment. The authors conclude that ERP is not an indication for further testing in athletes or for restricting their participation in sports [27-29].

Further in-depth investigations must be completed before emer- gency medicine providers can incorporate these principles into the evaluation of symptomatic athletes. No comprehensive studies have looked at sudden cardiac death specifically in athletes and, further, no detailed analyses have focused on the relationship between ERP in athletes and clinical outcomes. Certainly, the authors construct valid points but the clinical implications are still limited.


A. Adhikari S, Marx J, Crum T. Point-of-care ultrasound diagnosis of acute Achilles tendon rupture in the ED. Am J Emerg Med 2012;30(4):634.e3-e4

Acute Achilles tendon ruptures are often the result of repetitive overuse, commonly associated with running and jumping activities. Most ruptures occur 3 to 6 centimeters proximal to the calcaneal insertion point of the tendon, because of the large eccentric loads, hypovascularity, and the small cross-sectional area of that region [30]. Diagnosis is frequently limited by pain and swelling. Over 20% of Achilles tendon ruptures are missed initially [31].

Adhikari and colleagues present a case report involving a 39-year-old woman complaining of severe left leg pain, mostly in the posterior aspect of the ankle and calf. She had been experiencing this pain for about 2 hours before coming to the ED. The pain started while she was playing volleyball and landed off a jump. At presentation, the patient could not bear weight on her left leg. Her physical examination was limited due to her severe pain. Radiographs of the left ankle, tibia, and fibula were negative for acute fracture or dislocation.

The authors examined the patient’s Left lower extremity with bedside ultrasound. A 10- to 5-MHz linear array transducer was used to compare both ankles. The left ankle was found to have complete disruption of the fibrillar appearance of the tendon approximately 6 centimeters from the insertion site on the calcaneus. Retraction of the torn ends was also visualized, and the gap between the ends was filled with hematoma and debris. The authors were also able to provide some dynamic imaging with slight passive dorsiflexion to plantar flexion.

The sensitivity of ultrasound for Achilles tendon rupture is 96% to 100%, with a specificity ranging from 83% to 100%. The patient is typically scanned in the prone position, with the feet hanging over the edge of the bed. A high-frequency linear array transducer is used. In addition to disruption of the tendon on ultrasound, other findings suggestive of rupture are herniation of Kager’s fat pad into the tendon gap, hematoma formation at the site of rupture, posterior acoustic

shadowing at the margins of rupture, adjacent hypoechoic tendinosis, and visualization of plantaris tendon.

This case report highlights the utility of ultrasound in accurately identifying tendon rupture, what is commonly a challenging and often missed diagnosis. ED physicians should consider ultrasound evalua- tion when assessing patients with musculoskeletal complaints and normal radiographs. If injury is suspected, ultrasound could be the ED physician’s greatest diagnostic tool.


The manuscript was copyedited by Linda J. Kesselring, MS, ELS, the technical editor/writer in the Department of Emergency Medicine at the University of Maryland School of Medicine.


  1. Gilchrist K, Thomas K, Xu L. Nonfatal sports and recreation related traumatic brain injuries among children and adolescents treated in emergency departments in the United States, 2001-2009. MMWR 2011;60:1337-42.
  2. SCAT3(TM): Sport Concussion Assessment Tool – 3rd edition. Br J Sports Med 2013;47:259. Available at Accessed on July 10, 2013.
  3. Dvorak J, Junge A, Fuller C, McCrory P. Medical issues in women’s football. Br J Sports Med 2007;41(Suppl 1):i1.
  4. Dvorak J, McCrory P, Kirkendall DT. Head injuries in the female football player: incidence, mechanisms, risk factors and management. Br J Sports Med 2007;41(Suppl 1):i44-6.
  5. Gessel LM, Fields SK, Collins CL, Dick RW, Comstock RD. Concussions among United States high school and collegiate athletes. J Athl Train 2007;42:495-503.
  6. Leininger BE, Gramling SE, Farrell AD, et al. Neuropsychological deficits in symptomatic Minor head injury patients after concussion and mild concussion. J Neurol Neurosurg Psychiatry 1990;53:293-6.
  7. Lovell MR, Iverson GL, Collins MW, et al. Does loss of consciousness predict neuropsychological decrements after concussion? Clin J Sport Med 1999;9:193-8.
  8. Yarnell PR, Lynch S. Retrograde memory immediately after concussion. Lancet 1970;1:863-4.
  9. Yarnell PR, Lynch S. The ‘ding’: amnestic states in football trauma. Neurology 1973;23:196-7.
  10. Lovell MR, Collins MW, Iverson GL, et al. Recovery from mild concussion in high school athletes. J Neurosurg 2003;98:296-301.
  11. McCrory PR, Ariens T, Berkovic SF. The nature and duration of acute concussive symptoms in Australian football. Clin J Sport Med 2000;10:235-8.
  12. Meehan 3rd WP, Taylor AM, Proctor M. The pediatric athlete: younger athletes with sport-related concussion. Clin Sports Med 2011;30:133-44.
  13. Child-SCAT3(TM): Sport Concussion Assessment Tool for children ages 5 to 12 years. Br J Sports Med 2013;47:263. Available at full.pdf. Accessed on July 10, 2013.
  14. Covassin T, Stearne D, Elbin R. Concussion history and postconcussion neurocog- nitive performance and symptoms in collegiate athletes. J Athl Train 2008;43: 119-24.
  15. Bruce DA, Alavi A, Bilaniuk L, et al. Diffuse cerebral swelling following head injuries in children: the syndrome of “malignant Brain edema“. J Neurosurg 1981;54:170-8.
  16. McCrory PR, Berkovic SF. Second impact syndrome. Neurology 1998;50: 677-83.
  17. Guskiewicz KM, Marshall SW, Bailes J, et al. Association between recurrent concussion and late-life cognitive impairment in retired professional football players. Neurosurgery 2005;57:719-26.
  18. McKee AC, Cantu RC, Nowinski CJ, et al. Chronic traumatic encephalopathy in athletes: progressive tauopathy after repetitive head injury. J Neuropathol Exp Neurol 2009;68:709-35.
  19. Guskiewicz KM, McCrea M, Marshall SW, et al. Cumulative effects associated with recurrent concussion in collegiate football players: the NCAA Concussion Study. JAMA 2003;290:2549-55.
  20. Dryden DM, Saunders LD, Rowe BH, et al. The epidemiology of traumatic spinal cord injury in Alberta, Canada. Can J Neurol Sci 2003;30:113-21.
  21. Hu R, Mustard CA, Burns C. Epidemiology of incident spinal fracture in a complete population. Spine (Phila Pa 1976) 1996;21:492-9.
  22. Jackson AB, Dijkers M, Devivo MJ, et al. A demographic profile of new traumatic

    spinal cord injuries: change and stability over 30 years. Arch Phys Med Rehabil 2004;85:1740-8.

    2012-2013 NCAA Sports Medicine Handbook. Indianapolis, Indiana: National Collegiate Athletic Association; 2012.

  23. Corrado D, Basso C, Pavei A, et al. Trends in sudden Cardiovascular death in young competitive athletes after implementation of a preparticipation screening program. JAMA 2006;296:1593-601.
  24. Grant RP, Estes Jr EH, Doyle JT. Spatial vector electrocardiography: the clinical characteristics of S-T and T vectors. Circulation 1951;3:182-97.
  25. Noseworthy PA, Weiner R, Kim J, et al. Early repolarization pattern in competitive athletes: clinical correlates and the effects of exercise training. Circ Arrhythm Electrophysiol 2011;4:432-40.
  26. Tikkanen JT, Junttila MJ, Anttonen O, et al. Early repolarization: electrocardio- graphic phenotypes associated with favorable long-term outcome. Circulation 2011;123:2666-73.
  27. Tikkanen JT, Anttonen O, Junttila MJ, et al. Long-term outcome associated with early repolarization on electrocardiography. N Engl J Med 2009;361:2529-37.
  28. [29] Sinner MF, Reinhard W. Muller M, et al. Association of early repolarization pattern on ECG with risk of cardiac and all-cause mortality: a population-based prospective cohort study (MONICA/KORA). PLoS Med 2010;7:e1000314.
  29. Hess GW. Achilles tendon rupture: a review of etiology, population, anatomy, risk factors, and injury prevention. Foot Ankle Spec 2010;3:29-32.
  30. Hartgerink P, Fessell DP, Jacobson JA, et al. Full- versus partial-thickness Achilles tendon tears: sonographic accuracy and characterization in 26 cases with surgical correlation. Radiology 2001;220:406-12.