Soccer, or football, as it is known in much of the world, is one of the most popular sports in the world, with more than 265 million active recreational and amateur-level players worldwide, with approximately 27 million in Canada and the United States alone (13). The purpose of this article was to discuss and evaluate important and relevant findings on select soccer-specific medical issues published over the last year. Some of these findings are new, some build upon previous findings, and some confirm what has been found before. The hope is to provide a concise selective update on three different soccer-related subjects, as follows: soccer injury and prevention, concussion, and chronic groin pain.
Sports Injury and Prevention
Injury prevention continues to foster much attention in the media and among the health care community. The injury rate in professional soccer is estimated to be approximately 1,000 times higher than certain high-risk professions, such as those found in construction and manufacturing (8). Understanding how injuries occur is of importance, as there are negative consequences including suffering of injured players, medical costs, sports and work absenteeism, and financial loss (25). The health care cost of injuries has been looked at previously, including in Switzerland in 2010, where health care costs for soccer injuries amounted to almost USD 170 million, while others estimated the socioeconomic effect to exceed USD 30 billion worldwide (6,45). Injury incidence in adult male soccer players range from 1.8 to 7.6 injuries per 1,000 training hours and from 10.2 to 35 injuries per 1,000 match hours (20). It is no wonder that many of the studies in soccer focus on tracking and analyzing injury data, with emphasis on injury prevention research. It is through accurate injury tracking that we can see injury patterns that aid in the recognition of injury trends, directing further research, which leads to injury prevention interventions.
FIFA and UEFA Injury Studies
In the last 15 to 20 years, the importance of collaborative injury tracking has been emphasized and, in soccer, resulted in two large main international surveillance systems. One is organized by the Fédération Internationale de Football Association (FIFA), which began injury tracking in 1998, and the other is the Union of European Football Associations (UEFA) Champions League injury study, or UEFA injury study, that began in 2001 and has involved between 27 and 33 European soccer teams from 10 different countries over the past 11 seasons. With such large databases of information, there have been new insights into injury risk, injury incidence, and injury exposure specific to soccer. Injuries matter a great deal to these professional soccer teams due to costs and the downstream effect of individual and team performance. In professional soccer, a 25-player team can expect an average of two injuries per player, resulting in time loss for play (11). In other terms, 12% of the team may be unavailable at any point in the season due to injury (9). These sobering numbers help highlight the importance of the medical staff to a team. By succeeding in reducing injury rates and injury time off, the medical staff could have significant impact on team performance.
Junge et al., using data from FIFA, found that most injuries occurred in the lower extremities (70%), with the head and neck at 15%, the trunk at 8%, and the upper extremity at 7% (25). The most commonly diagnosed injuries were contusions (55%), sprains (15%), and strains (10%), which is similar to previous studies (11,21,26).
Most of the injuries, approximately 80%, occurred from contact with another player, with 47% of the contact injuries resulting from foul play (26). Contact in soccer cannot be avoided, but stricter enforcement of rules by referees may aid in decreasing injury as a result of contact.
Ekstrand et al. (9), with UEFA injury study data, found a decrease in the rate of ligament injuries over the 10 seasons but not in injury rates of muscle injury and severe injury. The most commonly injured ligaments include lateral ankle ligaments and medial collateral ligaments (MCL) of the knee, making up 11% of ligament injuries (9). Many of the injury prevention programs, such as those for anterior cruciate ligament (ACL) injury prevention, result in decrease in ligamentous injuries only. The effectiveness of current preventative programs in preventing muscle injury and severe injury is unclear. Playing and practice intensity has increased and may negate in some way some of the possible injury prevention benefits. One must consider the internal risk factors (such as strength, balance, coordination, and level of play) in relation to the less understood role of external risk factors (e.g., player load, game-match frequency) (9).
Lower Extremity Injury
The UEFA injury study looked at risk factors for lower extremity muscle injury, confirming that some previously known risk factors include previous injury, older age, and kicking leg. However specific to previous injury being a risk factor, one would assume the new injury to be a reinjury but the data showed otherwise, that any previous injury to other muscle groups in the lower extremity increased injury rates. This should emphasize that when rehabilitating an injury, focus on the site of injury must be balanced with a holistic injury prevention approach. A quadriceps strain could be the precursor to the ACL injury; the whole leg should be rehabilitated, not just the quadriceps (21). Return-to-play criteria warrant further study, as even its definitions can be so varied and unclear. Our threshold for return to play needs to be more than just absence of pain or return of strength to the injured site. More systematic evaluation, such as looking at the complete kinetic chain, may be of benefit for return-to-play criteria.
MCL, Achilles, and Ankle Injuries
In relation to the lower extremity, the UEFA injury study looked at multiple lower extremity injuries, but this article will focus on three different injury areas including the MCL, Achilles, and ankle injuries (14,33,48).
MCL injuries occurred most often in the last 15 min of the first or second half of the game, with 70% of the injuries occurring after contact, most commonly from a foul, with most occurring in the dominant leg (33). This finding is consistent with previous studies demonstrating an overall increase in injury toward the end of the first and second half (11). Being cognizant of higher-risk game periods is important in injury prevention. At times, many players may increase intensity of play at the end of game, especially when motivated by possible loss, leading to increased player fatigue (11). Fatigued players are more likely to break away from proper form, and the muscular protective effect is diminished. The combination of increased intensity and fatigue often leads to more fouls, which the UEFA injury study consistently found to increase injury risk. The practical application of alerting coaching staff to high-risk periods of injury for certain fatigued or injured players in a game setting may be difficult. Coach and staff awareness of such high-risk periods may help underscore the need for injury prevention strategies, such as the FIFA 11+.
Achilles Tendon Injuries
The UEFA injury study found that a team of 28 players would average 1 Achilles injury per season (14). In general, Achilles injuries are not common in soccer, making up only approximately 3.8% of all soccer injuries, with ruptures even less common. Older players are at higher risk for Achilles injuries, mostly tendinopathies, which tended to occur mostly in the preseason. Awareness of this trend during the preseason should be reflected in the training regimen. Achilles tendinopathy tends to be an injury that players try to play with; this is supported by the fact that there is a 27% recurrence rate when resting for less than 10 d (14). Too early return to play can be problematic. Van Beijsterveldt et al. (46) looked at recovery in Dutch amateur soccer players and found that 27.4%, although functionally able to return to play, still reported some symptoms. Too often, the multiple pressures of sport can lead either to underreporting by players or minimization of symptoms by medical staff, which return less-than-healthy players to the sphere of play where they are at higher risk of reinjury.
The UEFA injury found that three-quarters of ankle sprains were lateral ankle sprains, with only 5% being high ankle sprains. Foul play again was found to be a risk factor, as it was associated with 40% of ankle sprains (48). Interestingly posterior ankle impingement had a threefold-higher incidence than anterior ankle impingement. This is surprising, as anterior ankle impingement, also called footballer’s ankle, was thought to be more problematic and common (48).
Rest and recovery time is vital in the study of injury prevention. Fixture congestion, or playing multiple games in a short amount of time, appears to be related to higher injury risk. Bengstsson et al. (1) found that fixture congestion in professional soccer players increases muscle injury rates and total injury rates but did not seem to affect overall team performance. This relationship between team performance and injury is important. Successful teams have lower injury burden and higher match availability. The concept of injury burden includes not only injury incidence (frequency of injury in terms of hours of sports exposure) but also injury severity. Decrease in the number of injuries for a team could be negated by the severity of fewer injuries, which still would impact player match availability (12,22). A team tends to perform better if healthy. This simple truth, at times, can be overlooked by the medical staff on the sideline, as the focus is on diagnosing and treating the acute injury. There needs to be a team approach mindset, where everyone from the team physician to the athletic trainer to the physical therapist to the nutritionist has the optimization of health for each individual player as the goal. The medical staff should have a stake in how the team performs, with expected accountability from coach and players as well.
FIFA 11+ and Injury Prevention
One cannot discuss injury prevention in soccer without mentioning the FIFA 11+ Injury Prevention Program. The FIFA 11+ is a complete warm-up program with running exercises at the beginning and end to activate the cardiovascular system and specific preventative exercises focusing on core and leg strength, balance, and agility, with three levels of increasing difficulty to provide variation and progression (2). Multiple studies have shown the FIFA 11+ to be effective by helping from improvements in functional static/dynamic balance to reduced injury risk to enhanced neuromuscular control (4,41,44). Recently Grooms et al. (18) found that the FIFA 11+ did reduce overall risk and severity of lower extremity injury in collegiate male soccer players.
Part of the success, I believe, of the FIFA 11+ is the short time commitment, 20 min, minimal equipment, cones and ball, and minimal training to administer. Although it was created as a soccer-specific program, the FIFA 11+ contains principles that would help any athlete regardless of the sport. An example of this was a recent cluster randomized study that found the FIFA 11+ to be effective with male elite basketball players (32).
Despite its apparent ease of implementation, some key foundational principles should be followed, including compliance, advancing difficulty, and having someone trained administer and monitor the program and its effectiveness (18). These simple points must be taken into account when critically evaluating any injury prevention program. It can be easy to discount a specific warm-up program as ineffective if not done consistently. Time and commitment to doing the program are vital. As well as making sure to challenge neuromuscular control and balance continually, if the warm-up program in some way does not replicate the movement actions required by the sport, the transference from practice to real game situation will be very difficult to attain. Lastly there must be a measure of quality control to make sure not only that there is compliance with the warm-up program but also that it is done correctly, with proper form, recognizing when the athlete has reached a plateau and needs to be challenged further. Having proper body form during exercise with proper muscle activation at the right time is extremely important. One further step that could be taken would be to recognize an athlete struggling with form during the FIFA 11+ warm-up and engage them in further exercises to correct the deficits.
Soccer is one of the few, and if not the only, sports that requires specific purposeful use of the head to control and advance a ball (38). Therefore it is no surprise that players may be more vulnerable to head and neck injuries, which could include lacerations, abrasions, contusions, fractures, and concussions.
Heading involves active absorption, beginning with leg flexion and trunk extension, creating the necessary acceleration necessary to have the three stages of heading, which include preimpact, ball contact, and follow-through with the ball ideally striking at the front hairline (43).
Even though the head-to-ball contact occurs most often, it is not the main source of concussion-causing contact. Most concussions in soccer occur from head-to-player contacts (40%), followed by head-to-ball contacts (12.6%), and then head-to-ground or -post contacts (10.3%) (34,43)
More specifically, the side of the head is the most common area hit when concussions do occur with player-to-player contact. It could be that the inability to prepare for this side impact may stem from neck muscles that may not be activated in time to absorb some of the force (7). From previous studies, it is known that before ball impact, there is important contraction of neck musculature (27,29). One area of possible concussion prevention research would be to target the neck musculature not only in terms of strength but also neuromuscular reaction time. Addition of neck-specific exercises to the FIFA 11+ might lead to quicker response time, leading to possible decrease in concussion.
A recent UEFA injury study article looked at head and neck injuries data over a 9-year period in professional soccer (39). Head and neck injuries made up approximately 2% of all injuries, with concussions being one-third of the head and neck injuries, at a rate of 0.06 injuries per 1,000 h of exposure (39). Interestingly of 6,140 total injuries reported over the 9-year period in the UEFA injury study, only 48 were reported concussions (0.008%) (39). This astonishingly low number would lead one to believe that concussion either is underreported, is missed on evaluation, or does not occur in professional soccer truly frequently. The latter is unlikely, given previous concussion research in soccer showing a rate of 0.6 per 1,000 athlete/exposures (3). One would hope that if this study were to be repeated in 10 years, with sports concussion at the forefront of education, both medically and culturally, these numbers would reflect this discrepancy. Just as concerning, 27.1% of players with concussion returned within 5 d, which would indicate that 1 in 4 athletes with concussion are not returning to play according to current internationally recommended return-to-play protocol (37,39). Lastly of note, a 78-fold higher risk of concussion was seen during match play as compared with that during practice or training, with defenders being at greatest risk (39).
Much controversy in soccer has to do with heading, which some consider chronic low-level head trauma or subconcussive trauma that could lead to persistent cognitive decline. This has been emphasized as of late in the media with former National Football League (NFL) football players and the possible connection between concussions or brain trauma and chronic traumatic encephalopathy (CTE). Previous studies have suggested that subconcussive injuries in soccer can lead to accelerated cognitive decline (16,36), while other studies found that short-term and cognitive decline caused by head injury is only transient (30,50).
In the last year, studies that support both sides have been published. Zhang et al. (51) looked at the short-term impact of heading and found that even with subconcussive forces, soccer players had slower reaction times compared with controls using their tablet-based approach. Vann Jones et al. (47) did a self-assessment questionnaire with retired soccer players with the expectation of finding cognitive decline due to a career filled with heading but found similar scores as compared with the general population. This indicates that expected cognitive decline for subconcussive heading forces are either nonexistent or transient (47). The findings of these two studies contradict a very recent review by Maher et al. (34) that found most studies did not see a short-term cognitive effect of heading but did see a negative effect on various aspects of long-term neurocognitive performance in former long-time players. With such contradictory findings, needless to say, more research needs to be done to define cause and effect more clearly, if any. Hopefully this can be accomplished without the tainting effects and pressures of the media.
Concussion and imaging
Imaging research, as of late, is being done to assess the possible subconcussive trauma of heading. White matter changes on magnetic resonance imaging (MRI) with accompanying memory performance decline (as measured by neurocognitive testing) were found in soccer players and thought to be secondary to subconcussive heading. However these changes, similarly seen in patients with traumatic brain injury, were not at the point of ball/head impact but reflected a contrecoup injury pattern. The changes mostly were seen in players who headed >885 to 1,800 per year. Just as in concussions, a threshold at which these changes happen seems to exist and with some subjects having seemingly lower thresholds (31).
Further research is necessary to understand further both the possible short-term and long-term implications of heading. Once again, at present, the literature remains mixed, and no definitive connection between brain trauma and CTE has been found (23,37).
Tools, such as the recently updated Sports Concussion Assessment Tool 3 (19), can be used to evaluate an athlete after concussion, but additional tools to help evaluate possible subconcussive trauma are needed. Although MRI quality continues to progress, its use in the acute setting tends to be difficult. The possibility of using a tablet to perform real-time testing on the field is exciting. This would allow for real-time data, such as reaction time, allowing for an objective way to assess neurocognitive status on the sideline and help make decisions on whether a player should sit out; or similarly to pitch counts in baseball, there could be heading counts, with certain threshold that, if passed, would increase the risk of concussion greatly (31). These may be great areas for future research.
Concussions in children
Among children, soccer continues to be one of the most popular sports played. A recent review study, aside from highlighting the importance of treating children with concussion with more caution due to longer recovery times, emphasized the importance of returning to learning and school before returning to sport (35). School-aged patients are student-athletes — students first, and athletes second.
Adductor-related groin injuries are the second most common type of muscle injury in soccer and the most common hip or groin injury (10,49).
Yet chronic groin pain remains one of the most poorly understood clinical conditions, where diagnosis and treatment not only are challenging but also are varied widely. There is limited to no consensus on nomenclature, duration, diagnosis, cause, and management. Many use terms like sports hernia, Gilmore groin, and athletic pubalgia interchangeably when describing chronic groin pain in which no clinically detectable hernia is present. In fact, it seems that with each new published study, new proposed names for this groin pain pathology are created, such as that in the article of Cavalli et al. (5) who recently proposed “pubic inguinal pain syndrome,” while Garvey and Hazard (15) described it as groin disruption injury and Sheen et al. (42) and the British Hernia Society have labeled it as inguinal disruption (ID). More and more, the thinking is that there are various pathologies that form a clinical entity, instead of one sole cause of chronic groin pain. In a recent study, more than one clinical entity was found in 24% of players with groin injuries (24). Sources of pain may include posterior inguinal canal wall deficiency, conjoint tendinopathy, adductor tendinopathy, osteitis pubis, and peripheral nerve entrapment (15). Some have suggested that the most common entity of groin injury is the adductor, followed by the iliopsoas, then abdominal musculature, with injury to the dominant leg being the most common (24). Holmich et al. (24) found that recovery time is quadrupled if both adductor and abdominal muscles are involved.
Groin injury risk factors
Some of the known risk factors for chronic groin pain include pelvic instability, adductor muscle imbalance, reduced hip join range of motion, delayed core stability, and previous groin injury (15). Although no clear mechanism of injury is understood at this time, what is known is that sporting activities that involve pivoting or a single leg or sudden changes in direction at speed present greater risk (15). This description is applied easily to soccer.
Groin injury and imaging
Deciding on imaging in chronic groin pain can be confusing, leading many times to clinical decision dilemma. In general, the two most common imaging studies used are ultrasound and MRI.
Some who propose ultrasound as the imaging of choice believe that a sports hernia only can be diagnosed when, while straining the abdomen, a bulge of the posterior inguinal wall is visualized by ultrasound (15,17).
Although ultrasound is promising, with its cheaper cost, it depends a great deal on the skill set and experience of the individual performing the ultrasound, making it very dependent on the operator.
On the other hand, MRI for chronic groin pain requires similar skilled reading, as the findings can be subtle, making the whole clinical picture even more challenging (40).
British Hernia Society and ID
Lastly it is important to touch upon some of the key findings by the British Hernia Society position statement on the treatment of sportsman’s hernia. As mentioned previously, they recommended ID as a new term, removing the word hernia because a classic hernia is found rarely. They presented a definition and five clinical signs, with a minimum of three needing to be present for ID diagnosis (Table 1) (42).
In terms of pathology, they found an overall posterior wall weakness, external ring dilation, conjoint tendon damage, and, many times, tears in the inguinal ligament (42).
In relation to imaging, the position statement recommended MRI as the primary choice for evaluation, with ultrasound being secondary. They found that athletes <18 years of age most commonly have diffuse bilateral edema equivalent to a stress response, while in athletes >18 years of age, more focal edema in the subcortical bone and capsule/enthesis, usually bilateral but asymmetrical (42).
Treatment, in most instances, should begin with a trial therapy for 2 to 4 wk, with surgery as a secondary option (42). The trial of therapy seems to be shorter than that suggested by others such as Garvey and Hazard (15) who found that a 3- to 6-month trial of therapy was needed to ascertain success or failure of therapy. Garvey and Hazard (15) found similar resolution of symptoms whether therapy or surgery was performed but did note quicker return to play following surgery. If treatment does come to surgery, the British Hernia Society found that despite the wide range of surgical approaches that are performed today, no one technique, whether open or laparoscopic, has been shown to be superior, although use of mesh was recommended (42). One recent study by Larsen (28) quoted that regardless of surgical technique, success was found to be >80%, and noted the lack literature on success rates of nonsurgical approach.
One last important point is recognizing the need for a multidisciplinary approach where physical therapists, athletic trainers, sports medicine physicians, and hernia surgeons work together with the aid of radiological imaging (42). This is a disease process that would benefit from the use of an algorithm to help decisions along the way, as it can become easy to get lost in its complexity (Table 2).
Soccer, not unlike many other sports, has continued to develop and change. Advancements in training only have increased the intensity of play. Continued vigilance in these changes with accurate up-to-date understanding of new and upcoming research is vital. The importance of injury surveillance is not only in the collection of data but also in the analysis of data, with the hope of understanding past and present trends and maybe even predicting futures ones. Only then are we able to plan and implement prevention strategies effectively. This can be done through physical preparedness interventions such as the FIFA 11+ or, possibly, implementation of a heading count system with possible real-time sideline tablet-based neurocognitive testing to further characterize a poorly understood injury, like chronic groin pain.
The authors declare no conflicts of interest and do not have any financial disclosures.
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