Historical Considerations

Many athletes, coaches, and health care providers are likely familiar with the 3-strike rule, a guideline adopted by many athletic organizations that recommends removing an athlete from contact sports for at least the remainder of a season after 3 concussions. Historically, this 3-strike rule was founded on an article published in 1952 by Augustus Thorndike. Based on his experience caring for athletes at Harvard University, Thorndike recommended that athletes retire from contact sports after 3 concussions of moderate severity. An important consideration is that definitions for concussion contemporary with Thorndike’s publication involved a loss of consciousness (LOC) or amnesia. Although the definition for concussion has evolved in the decades following this publication, the 3-strike rule has remained a commonly accepted indication for retirement among the general public and even some health care providers, despite its origin as expert opinion.

In the 1980s and 1990s, efforts were made to classify concussions based on severity and thereby assist clinicians in determining RTP timing and athlete retirement after SRC. At least half a dozen grading scales emerged during this period, most of which used the presence of confusion, amnesia, and LOC as factors to determine concussion severity. Although some of these classification systems made recommendations for immediate management of concussions based on grade, most did not address athlete retirement. In 1998, Dr Robert Cantu published guidelines ( Table 1 ) for short-term and long-term retirement from contact sports using a concussion grading system he originally created in 1986.

In 2001, the inaugural International Conference on Concussion in Sport was held in Vienna to create consensus recommendations on the definition, diagnosis, and management of SRC. This Concussion in Sport Group (CISG) defined concussion as a “complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces.” Although the CISG acknowledged that there were strengths and weaknesses to contemporary concussion grading systems, they ultimately did not endorse a grading or classification system for concussions and instead recommended that health care providers treat each case of SRC individually and use clinical judgment to determine prognosis. Also in 2001, Paul McCrory authored an editorial wherein he emphasized the lack of scientific evidence for the 3-strike guidelines and arbitrary exclusion periods. Echoing the sentiments of the CISG, he called for a more individualized approach to athlete disqualification and retirement based on thorough clinical and neuropsychological evaluation. As such, grading scales, the 3-strike rule, and other categorical retirement tools gave way to a more individualized approach.

Numerous factors may influence a sport retirement decision after SRC, including athlete age, relevant medical history, sport, position, and level of play, as well as severity and duration of concussion symptoms and results of neuroimaging and neuropsychological testing, if performed. This article explores considerations pertaining to athletes’ own medical and concussion histories, as well as external factors that influence sport participation. A summary of proposed contraindications to continued sports participation after SRC published in the last decade is given in Table 2 . Importantly, these are still based on expert opinion, and retirement after SRC remains an area for future research, which is likely to evolve with the understanding of SRC and related outcomes.

Concussion History

Despite the trend away from using only an athlete’s total number of SRCs as the criterion for retirement, concussion history is typically still considered as 1 factor in the decision. For example, various experts suggest disqualification after multiple concussions in the same athletic season, although the exact number is debated. ^{, ,} Sedney and colleagues recommended that 3 concussions, or 2 concussions with symptom duration longer than 1 week, sustained in a single season should result in disqualification for the remainder of the season. A more conservative approach has generally been advised in younger athletes, with experts advising retirement for the remainder of a sports season after 2 concussions sustained in a single season. ^, Presumably, this recommendation is intended to reduce head injury risk for the remainder of the season and allow the athlete to RTP in a future season, likely many months in the future. However, this recommendation does not take into account multisport athletes or athletes who participate in sports year-round, as is often encountered in a youth, high school, or collegiate sports setting. In these cases, health care providers may consider timing between injuries (ie, weeks or months) as a factor in return-to-sport decisions, rather than the specific sport season when the injuries occurred.

Guskiewicz and colleagues provided clinical evidence of a vulnerable period after return to sport in their 2003 study, because more than 90% of within-season repeat concussions in college football athletes occurred within 10 days of the initial injury, at an average interval of 5.6 days (average RTP at 3 days postinjury). Interestingly, a similar study published in 2020 suggests that a symptom-free waiting period (SFWP) before full return to sport, such as the RTP strategy published in the most recent CISG consensus statement, can significantly reduce the overall number of repeat concussions in the same season and extend average time between within-season concussions to 56.4 days (average RTP time at 12 days postinjury, with mean SFWP of 6 days). Note that concussion management has also become more conservative over the same time frame, in that athletes are not returned to play on the same day that they have sustained a concussion. Further research is needed to understand optimal timing for RTP after SRC, especially for athletes with multiple injuries in the same season; however, the evidence discussed earlier supports the use of a graduated RTP strategy after recovery from SRC.

Concern has been raised for cumulative effects of multiple concussions, where athletes show an increased risk of subsequent concussion, worse symptom severity, and longer duration of recovery with increasing number of concussions. Limited data in pediatric concussion suggest longer recovery when concussions occur less than 12 months apart, but more favorable recovery profiles when concussions were separated by more than a year. In contrast, other studies have found faster recovery for subsequent concussions compared with initial injury, or no difference in recovery for patients with and without history of previous concussion. A few researchers have evaluated the effect of previous concussion history on preseason testing in an attempt to understand residual effects of concussion. Various studies in both high school and college athletes have found that history of 1 or more prior concussions did not influence preseason symptoms, neurocognitive performance, or postural stability, relative to athletes without history of concussion. Notably, minimal evidence exists for athletes with more than 3 concussions, so further research is needed in this area to ascertain the impact of multiple concussions on athlete function and recovery.

Persistent Postconcussion Symptoms

The concept that athletes should not be returned to sport training or competition while still symptomatic from a concussion is broadly accepted in management of SRC. ^, For most athletes, recovery is rapid, within a few days to weeks, followed by return to sport after full recovery and completion of a graduated RTP strategy. Challenges arise when determining participation status in the setting of prolonged recovery. Historically, prolonged concussion symptoms have been proposed as criteria for sport retirement, ^{, ,} even once the athlete has fully recovered. Important to consider is that the criteria for prolonged symptoms have changed over the years, and have been inconsistently defined. Although postconcussion syndrome has often been defined as symptoms greater than 3 months in duration following concussion, currently experts favor terminology of persistent postconcussion symptoms (PPCS), which refer to symptoms persisting beyond the typical recovery period (10–14 days in adults, and up to 4 weeks in children).

PPCS have a variety of causes, related to both injury and noninjury factors. ^, Preexisting conditions, such as migraines, sleep disorders, depression, or anxiety, have been associated with higher symptom burden and longer recovery ^, and can complicate the determination of when an athlete has recovered from concussion. As such, involvement of a multidisciplinary team is often beneficial to help understand the contributing factors to PPCS and develop a management strategy. Given the complexity of PPCS, some experts propose that prolonged recovery from a single concussion by itself should not be grounds for retirement, as long as the athlete is fully recovered at the time of return to sport. In contrast, a pattern of prolonged recovery occurring with each injury in the setting of multiple concussions or concern for decreased injury threshold may result in a retirement recommendation. ^, Therefore, as the understanding of concussion progresses, it is apparent that concussion retirement guidelines must also evolve.

More recently, aerobic exercise has been identified as an effective intervention to reduce symptom severity and duration in the treatment of PPCS. ^, However, this can create a challenge for clinicians, because athletes and coaches may interpret initiation of a sub–symptom threshold aerobic exercise training program as the start of a graduated RTP strategy. As such, careful education and consistent follow-up are needed to ensure athletes engage in appropriate exercise type, duration, and intensity during recovery, and do not prematurely return to sport before medical clearance.

Neuroimaging

Neuroimaging is not required for diagnosis of SRC, and is not routinely indicated in the acute evaluation of SRC, given the lack of characteristic brain imaging findings with this injury. However, a computed tomography scan may be used when there is concern for skull fracture or more severe brain injury in the acute setting after a head injury. MRI may be considered in the setting of focal neurologic deficits, protracted recovery, or other atypical presentation of SRC. Of note, many neuroimaging findings that are considered to be indications for retirement are related to more severe brain injury than a concussion, or are structural abnormalities that are unrelated to the injury but may have been found incidentally on neuroimaging studies performed after the injury (see Table 2 ). Athletes with abnormalities on neuroimaging, whether traumatic or not, may benefit from consultation with a neurosurgeon to help weigh the risks of return to sport specific to their individual case.

Neuropsychological Evaluation

Neuropsychological testing may be undertaken for athletes with a history of multiple concussions or prolonged recovery, to help understand the impact on cognitive and psychological functioning. Incomplete recovery after concussion with respect to academic, cognitive, social, or psychological function may be objectively understood through neuropsychological testing and may help identify noninjury factors, such as preexisting conditions (eg, learning disability, attention deficit disorder, mood disorder), or external factors (eg, litigation, psychosocial stressors) that influence recovery. ^, Persistent impairment on neuropsychological testing following concussion is considered by many to be grounds for sport retirement. ^{, , ,}

External Influences

Retirement from sport because of concussion is a complex decision, often influenced by the same people who supported the athletes during their playing careers. In addition to the athlete, family members, peers, coaching staff, and health care providers, including team physicians and athletic trainers, as well as concussion specialists, may contribute to the discussion leading to medical retirement. Family and peer groups may both exert influence on youth and adult athletes alike in a retirement decision. The decisions of teammates or other prominent athletes within a given sport may influence an athlete’s retirement decision. Several well-known athletes who sustained multiple concussions have withdrawn from play to prevent further injury; others have electively curtailed successful careers to preserve their health despite not sustaining major injuries. The impact of these highly publicized decisions is not well understood.

Coaching staff can also influence an athlete facing a potentially career-limiting injury. Because part of a coach’s success depends on the health and maximal performance of the athletes, a coach may unduly influence athletes to push through injury and tolerate continued or compounding risk if an athlete’s overall performance is not impaired by a current injury. A coach’s preference regarding retirement may also influence health care providers when making decisions about return to sport.

Amateur athletes pursuing professional athletic careers may make participation decisions based on their potential, both as a future athlete and a person with a life after sport. At times, a collegiate athlete may disagree with a disqualification decision and seek to transfer to a different institution willing to allow continued participation. Presently, a clear way for medical staff to communicate reasons for medical disqualification to other institutions does not always exist, especially in the setting of laws surrounding medical privacy.

Voluntary or athlete-initiated retirement may result in better outcomes for the athlete’s psychosocial well-being. The athlete’s personal sport-related and nonathletic goals and risk tolerance directly affect this decision. In general, the risk of future harm to an injured athlete is not precisely quantifiable and health care providers can help guide discussion surrounding this topic based on available evidence. The risk tolerance of health care providers varies and can influence their recommendations regarding an athlete’s continued participation.

Despite risks inherent in sport participation, the benefits of physical activity are numerous. In addition, sport is often a core component of an athlete’s identity, and medical retirement may be accompanied by poor adjustment or mood changes. However, there exists a growing awareness of the public health concerns surrounding concussion and other leading causes of medical retirement. Protection from further injury and minimizing risk of long-term complications remain common goals between self-retiring athletes and those athletes for whom health care providers mandated disqualification from play. There may be a role for programs that help athletes adapt to life outside of sports, emphasize new pursuits, and provide resources for coping, and opportunities for connection and social support. These efforts, along with follow-up care of medically retired athletes, are particularly important to protect and promote the health and well-being of the athletes.

Professional Athletes

The decision to retire from sport after SRC may be slightly different for professional athletes given the employment and career implications. Athletes may not want to disclose their histories if they think it will decrease their ability to be drafted and/or remain on the roster. Professional athletes whose financial stability depends on continued play may have an incentive to participate for as long as possible despite health risks. For example, under-reporting of concussions of National Football League players has been prevalent in the past. Health care providers taking care of professional athletes should provide athletes with the information that they have regarding their injuries, and support the athlete’s decision making related to risks and benefits of continued participation, using a shared decision-making model.

Pediatric Athletes

Given the young age at which many athletes begin sports participation, as well as recent trends of increasing year-round sport participation and sport specialization in youth sports, it is common for providers to encounter young athletes who have sustained multiple concussions. Consensus guidelines advise a more conservative approach for RTP in children and adolescents ; however, minimal evidence is available to guide decisions in this population. Similar to their adult counterparts, pediatric athletes should be managed on an individualized basis, taking into account the various factors mentioned earlier. Other factors that may be relevant to consider in pediatric athletes include expected physical and cognitive growth and development, competitive level, sport specialization, year-round participation, anticipated length of future risk exposure (ie, remaining competitive career), and the potential risk of head injury in other settings, including physical education class, recreational activities (riding a bicycle, jumping on a trampoline), as well as nontraditional sports such as skiing and snowboarding, skateboarding, and motocross. In some cases, young athletes may consider changing to a less competitive league, decreasing the amount of time spent in sport participation, or switching to a lower-risk position in their sport, as a means of modifying future head injury risk.

Current recommendations indicate that there is no evidence to support a total number of concussions (lifetime or otherwise) that necessitates sport retirement in pediatric athletes. ^, However, health care providers should acknowledge the lack of evidence and assist the athletes and their parents in weighing the potential risks and benefits of continued sports participation in a shared decision-making model, with experts advocating that the future health of the patient be the major focus of the decision. ^, An important consideration for all athletes, but especially for youth athletes, is the potential negative consequences of sport retirement on regular physical activity. Given the increasing trend of sedentary behavior and obesity, and their associated health risks, participating in regular physical activity in childhood and adolescence should be encouraged. Health care providers should help young athletes identify other athletic or physical activity pursuits in the event of contact/collision sport retirement. In addition, because previous concussion has been associated with emergence of mental health concerns, ^, for reasons that are not fully understood, the psychological health of young athletes should be monitored, especially in the setting of sport retirement.