Descriptive Epidemiology of Collegiate Men's Soccer Injuries: National Collegiate Athletic Association Injury Surveillance System, 1988–1989 Through 2002–2003

Abstract

Objective: To review 15 years of National Collegiate Athletic Association (NCAA) injury surveillance data for men's soccer and to identify potential areas for injury prevention initiatives.

Background: The NCAA sanctioned its first men's soccer championship in 1959. Since then, the sport has grown to include more than 18 000 annual participants across 3 NCAA divisions. During the 15 years from 1988–1989 to 2002–2003, the NCAA Injury Surveillance System accumulated game and practice injury data for men's soccer across all 3 NCAA divisions.

Main Results: The injury rate was 4 times higher in games compared with practices (18.75 versus 4.34 injuries per 1000 athlete-exposures, rate ratio = 4.3, 95% confidence interval = 4.2, 4.5), and preseason practices had a higher injury rate than in-season practices (7.98 versus 2.43 injuries per 1000 athlete-exposures, rate ratio = 3.3, 95% confidence interval = 3.1, 3.5). In both games and practices, more than two thirds of men's soccer injuries occurred to the lower extremities, followed by the head and neck in games and the trunk and back in practices. Although player-to-player contact was the primary cause of injury during games, most practice injuries occurred without direct contact to the injured body part. Ankle ligament sprains represented the most common injury during practices and games, whereas knee internal derangements were the most common type of severe injury (defined as 10+ days of time loss).

Recommendations: Sprains, contusions, and strains of the lower extremities were the most common injuries in men's collegiate soccer, with player-to-player contact the primary injury mechanism during games. Preventive efforts should focus on the player-to-player contact that often leads to these injuries and greater enforcement of the rules that are in place to limit their frequency and severity. Emphasis also should be placed on addressing the high rate of first-time and recurrent ankle ligament sprains.

T he National Collegiate Athletic Association (NCAA) conducted its first men's soccer championship in 1959. By the 1988–1989 academic year, 543 schools were sponsoring varsity men's soccer teams with approximately 14 000 participants. In the 2002–2003 academic year, the number of varsity teams had increased 35% to 732 varsity teams, with approximately 18 500 participants. Participation growth during this time has been apparent in all 3 divisions but particularly in Division III.

SAMPLING AND METHODS

Over the 15-year period from 1988–1989 through 2002– 2003, an average of 13.4% of schools sponsoring varsity men's soccer programs participated in annual NCAA Injury Surveillance System (ISS) data collection. ( Table 1). Men's soccer data were not collected in 2003–2004 due to pilot testing for conversion to a Web-based system. The sampling process, data collection methods, injury and exposure definitions, inclusion criteria, and data analysis methods are described in detail in the “Introduction and Methods” article in this special issue. ²

Table 1. School Participation Frequency (in Total Numbers) by Year and National Collegiate Athletic Association (NCAA) Division, Men's Soccer, 1988–1989 Through 2002–2003*.

RESULTS

Game and Practice Athlete-Exposures

The average annual number of games, practices, and athletes participating for each NCAA division, condensed over the study period, are shown in Table 2. Division III had fewer annual practices than Divisions I and II but a similar average number of participants per individual game or practice.

Table 2. Average Annual Games, Practices, and Athletes Participating by National Collegiate Athletic Association Division per School, Men's Soccer, 1988–1989 Through 2002–2003.

Injury Rate by Activity, Division, and Season

Game and practice injury rates over time combined across divisions are displayed in Figure 1 with 95% confidence intervals (CIs). The rate of injury was more than 4 times higher in a game than in a practice (18.75 versus 4.34 injuries per 1000 athlete-exposures [A-Es], rate ratio = 4.3, 95% CI = 4.2, 4.5). No significant linear downward trend was noted in either activity over time.

Figure 1. Injury rates and 95% confidence intervals per 1000 athlete-exposures by games, practices, and academic year, men's soccer, 1988–1989 through 2002–2003 (n = 6693 game injuries and 6281 practice injuries). Game time trend, P = .37. Average annual change in game injury rate = −0.7% (95% confidence interval = −0.8, 2.3). Practice time trend, P = .84. Average annual change in practice injury rate = −0.1% (95% confidence interval = −1.1, 1.4) .

The total number of games and practices and associated injury rates condensed over years by division and season (preseason, in season, and postseason) are shown in Table 3. Over the 15 years of the study, 6693 injuries from more than 22 000 games and 6281 injuries from more than 62 000 practices were reported. Practice ( P = .03) and game ( P < .01) injury rates differed across divisions. Game injury rates were lower in Division III than in the other 2 divisions (Division I versus Division III: 21.92 versus 15.76 injuries per 1000 A-Es, rate ratio = 1.4, 95% CI = 1.3, 1.5, P < .01; Division II versus Division III: 20.43 versus 15.76 injuries per 1000 A-Es, rate ratio = 1.3, 95% CI = 1.2, 1.4, P < .01). Practice injury rates had a similar pattern (lower in Division III than in Divisions I and II). Across divisions, preseason practice injury rates were more than 3 times higher than those during the regular season (7.98 versus 2.43 injuries per 1000 A-Es, rate ratio = 3.3, 95% CI = 3.1, 3.5, P < .01) or postseason (7.98 versus 1.62 injuries per 1000 A-Es, rate ratio = 4.9, 95% CI = 3.9, 6.2, P < .01). In-season game injury rates were significantly higher than those in the postseason (18.91 versus 14.58 injuries per 1000 A-Es, rate ratio = 1.3, 95% CI = 1.1, 1.5, P < .01).

Table 3. Games and Practices With Associated Injury Rates by National Collegiate Athletic Association Division and Season, Men's Soccer, 1988–1989 Through 2002–2003*.

Body Parts Injured Most Often and Specific Injuries

The frequency of injury to 5 general body parts (head/neck, upper extremity, trunk/back, lower extremity, and other/system) for games and practices with years and divisions combined is shown in Table 4. At least two thirds of all game and practice injuries were to the lower extremity. The second-highest body area at risk for injury was the head and neck in games and the trunk and back in practices.

Table 4. Percentage of Game and Practice Injuries by Major Body Part, Men's Soccer, 1988–1989 Through 2002–2003.

The most common body part and injury type combinations for games and practices with years and divisions combined are displayed in Table 5. All injuries that accounted for at least 1% of reported injuries over the 15-year sampling period are included. Ankle ligament sprains and knee internal derangements combined (see the “Introduction and Methods” article for the definition of knee internal derangement) accounted for 28.0% of game injuries, with concussions accounting for another 5.8%. Ankle ligament sprains and upper leg muscle (quadriceps and hamstrings) strains totaled 34.0% of practice injuries, with concussions totaling another 1.8%. Compared with practice, a participant in a game was 4 times as likely to receive an ankle ligament sprain (3.19 versus 0.76 per 1000 A-Es, rate ratio = 4.2, 95% CI = 3.9, 4.5), 6 times as likely to receive a knee internal derangement injury (2.07 versus 0.33 per 1000 A-Es, rate ratio = 6.3, 95% CI = 5.6, 7.0), and more than 13 times as likely to receive a concussion (1.08 versus 0.08 per 1000 A-Es, rate ratio = 13.5, 95% CI = 10.9, 16.6). Recurrent sprains accounted for 24% of all ankle ligament sprains. Ankle ligament injuries were not differentiated into medial versus lateral sprains or pronation versus supination mechanisms.

Table 5. Most Common Game and Practice Injuries, Men's Soccer, 1988–1989 Through 2002–2003*.

Mechanism of Injury

The 3 primary injury mechanisms—player contact, other contact (eg, balls, goals, ground), and no contact—in games and practices with division and years combined are displayed in Figure 2. Most game injuries (61%) resulted from contact with another player, whereas the majority of practice injuries (47%) resulted from injury mechanisms that did not involve direct contact to the injured body part (“no contact”).

Figure 2. Game and practice injury mechanisms, all injuries, men's soccer, 1988–1989 through 2002–2003 (n = 6693 game injuries and n = 6281 practice injuries). “Other contact” refers to contact with items such as balls or goals or with the ground. Injury mechanism was unavailable for 1% of game injuries and 4% of practice injuries.

In both games and practices, most other-contact injuries occurred through contact with the surface. Fewer than 1% of reported injuries in either games or practices (39 total injuries) over the 15-year period were associated with contact with the goal. Approximately 16% of all game injuries were associated with either attempting or receiving a slide tackle (data not shown).

Over the reporting period, 80.6% of reported concussions in games occurred from player contact, 8.0% from contact with the ball, and 8.0% from surface contact ( Figure 3). Anterior cruciate ligament (ACL) injuries were infrequent (accounting for fewer than 1% of reported injuries in either games or practices). As Figure 4 indicates, most ACL injuries in games were associated with player contact (46.2%).

Figure 3. Game concussion injury mechanisms, men's soccer, 1988–1989 through 2002–2003 (n = 387).

Figure 4. Game anterior cruciate ligament injury mechanisms, men's soccer, 1988–1989 through 2002–2003 (n = 104).

Severe Injuries: 10+ Days of Activity Time Loss

The most common injuries that resulted in at least 10 consecutive days of restricted or total loss of participation and their primary injury mechanisms, combining divisions and years, are displayed in Table 6. Time loss of 10+ days was, for this analysis, considered a measure of severe injury. Approximately 17% of game and practice injuries restricted participation for at least 10 days (18.7% of game injuries, 14.6% of practice injuries). Knee internal derangements and ankle ligament sprains accounted for the majority of these injuries in both games and practices. A total of 48.1% (586/1219) of all knee internal derangements in either games or practices resulted in time loss of 10 or more days, whereas only 15.2% (340/2231) of ankle ligament sprains were that severe (data not shown). Only 3.9% of all severe game injuries were concussions that limited participation for 10 or more days. Player contact was the primary injury mechanism for all the severe game injuries except for upper leg strains; noncontact mechanisms were the primary injury mechanism for all severe practice injuries except ankle ligament sprains, which were associated most often with player contact.

Table 6. Most Common Game and Practice Injuries Resulting in 10+ Days of Activity Time Loss, Men's Soccer, 1988–1989 Through 2002–2003.

Shin-Guard Rule

For the 1991–1992 season, shin guards became required equipment in games. Grouping all lower leg fractures, lower leg contusions, and ankle contusions sustained during games for the 3 years before the rule change (1988–1989 through 1990–1991) and the 12 years after the rule change (1991–1992 through 2002–2003) demonstrated no significant difference ( P = .60) in the injury rates (1.6 versus 1.5 injuries per 1000 A-Es; data not shown).

COMMENTARY

Injury rates in men's soccer over the past 15 years have remained relatively stable. More than two thirds of all injuries occur to the lower extremities, specifically the ankle, knee, thigh, and hip. The risk of injury was 4 times higher during games compared with practices, and preseason practices had a higher injury rate than in-season practices. Whereas player-to-player contact was the primary cause of injury during games, most practice injuries occurred without direct contact to the injured body part. Ankle ligament sprains represented the most common injury during practice and games (with 24% being recurrent), whereas knee internal derangements were the common type of injury resulting in 10 or more days of lost time.

Although variations in injury and exposure definitions make direct comparisons with previous research difficult, these results support previous findings in men's soccer. ^3–5 Furthermore, the trends and the specific injuries identified are, for the most part, consistent with our clinical practice. For example, ankle ligament sprains, specifically lateral ankle sprains, are a constant injury presence in soccer. Even though the initial time loss from ankle ligament sprains is less ominous than that for knee internal derangements, the high frequency and recurrence rate establish it as one of our primary clinical concerns. Muscle injuries to the hip and thigh and lower leg contusions also constitute a large portion of the injuries we treat. The proportion of injuries that resulted from direct contact and the types of injuries we see from slide tackles also are reflected in these results. Injuries such as concussions, contusions, knee internal derangements, and ankle ligament sprains are most often the result of direct contact with another player. It was also interesting to note that during practice, the injury rate for heat illness was nearly identical to that of concussions (0.07 versus 0.08 per 1000 A-Es), yet in most regions of the country, the environmental conditions that predispose players to heat illness have a very short time span relative to the length of an entire season. Although concussions continue to be a prominent concern in soccer, most were caused by player-to-player contact (84%) during games and not by contact with the ball (8%). This finding supports research suggesting that repetitive heading (ie, using the head to strike the ball) does not produce concussions or acute neurocognitive impairments. ^{6, 7} Moreover, the data do not allow for detailed interpretation as to whether the ball-to-head contact during an incidence of heading was intentional or accidental.

Due to the profound contribution of player-to-player contact to injury risk, we would expect to see differences between game and practice injury rates. Our clinical experience also supports the increased injury rate during preseason practice compared with in-season practice. During preseason practice, conditioning, increased intensity, scrimmaging, heat, and fatigue are risk factors that may contribute to the increased injury rate.

However, several injuries we treat consistently appear to be underrepresented in these results. For example, low back pain, a common malady for soccer players, represents a surprisingly low percentage according to these results. Various foot and toe injuries, both chronic and acute, also appear somewhat underreported. It is likely that these injuries, although common, do not consistently result in missed game or practice time; therefore, they were not highlighted in these results. In addition, sport hernias, a relatively new injury classification and a condition diagnosed frequently in soccer players, are not identified in these data. Traditionally, sport hernias would have been identified as hip flexor or abdominal strains in the ISS.

These results also provide some insight into the value and magnitude of our preventive efforts in reducing injury rates over the past 15 years. Despite rule modifications and a greater understanding of injuries such as ACL tears and concussions, the decreasing trends in game and practice injury rates over 15 years did not approach statistical significance. Furthermore, no significant or consistent declines followed any specific year. Thus, rule changes, improvements in conditioning and training, and a greater understanding of injury mechanics may have a gradual beneficial effect, rather than a sudden and dramatic benefit. This notion supports Dvorak et al, ⁸ who suggested that a multifaceted prevention approach can reduce soccer injury rates, but one specific intervention cannot be singled out. Just as a culmination of factors may predispose a soccer player to injury, ⁸ it is reasonable to suggest that a culmination of rule changes and other preventive measures have and will continue to have a positive effect on the overall injury rate in male soccer players without producing a drastic decline in any single season. With an appreciation for the potential cumulative effect of our preventive interventions, we draw attention to several specific areas.

Most injuries in men's soccer affect the lower extremity and result from player contact during games. Contact is a key factor in contusions, ankle ligament sprains, knee internal derangements, and even concussions. Therefore, revisiting the rules that address tackling and violent charging would be a reasonable strategy. More specifically, 16% of all game injuries occurred from slide tackles. This high percentage would seem to focus attention on the rules addressing slide tackles. When executed to perfection, slide tackles are some of the most exciting and skilled plays of the game. When performed incorrectly, they can cause the most violent and dangerous collisions we witness. Athletic trainers frequently treat serious lower extremity injuries resulting from slide tackles, many of which are not considered foul play. The 2006 NCAA Soccer Rules and Interpretations do not address slide tackles specifically. Tackling, in general, is addressed only under misconduct and exclusively as it pertains to tackling from behind. Tackling from behind is not considered a violation unless the tackle “is violent with little or no attempt to play the ball.” ⁹ However, Giza et al ¹⁰ found that the most dangerous slide tackle occurs not from behind, as the rules might suggest, but rather from the side. Furthermore, in a retrospective analysis of injuries related to tackling in international Fédération Internationale de Football Association (FIFA) matches, Fuller et al ¹¹ found that just over 25% of all injuries that occurred from tackling were caused by slide tackles. Boden et al ¹² reported that slide tackles were the most common mechanism resulting in tibial and fibular fractures. The 2005 FIFA “Laws of the Game” ¹³ also do not address slide tackles and offer only an interpretation similar to that of the NCAA rules: that tackling is a violation if the player contacts the opponent before the ball or if the tackle endangers the opponent. Andersen et al ¹⁴ and Fuller et al ¹⁵ concluded that the rules of the game may need to be reevaluated because many injuries occur during violent plays that do not constitute foul play. Already, throughout the United States, slide tackling has been banned in many adult recreational, intramural, and youth leagues. Revising the rules addressing violent charges in general and slide tackles specifically to strictly prohibit contact from the side would seem reasonable, as would harsher penalties for infractions.

An additional aspect of soccer injury prevention from contact is the mandatory use of soccer shin guards. Shin guards were mandated officially in 1991, but they were only required to be worn as part of the uniform, with no mention of size or structure. Interestingly though, as these results indicate, no immediate or recognizable reduction in the ankle and lower leg injury rate coincided with the mandatory wearing of shin guards. Shin guards are designed to minimize the risk of contusions and fractures of the lower leg. Researchers have suggested, however, that 84% ¹⁶ to 87% ¹² of lower leg fractures occurred while shin guards were worn. The NCAA shin-guard rule has evolved over the past 15 years to specifically address size and structure, leading to the most recent amendment, which states, “Beginning with the 2007 Fall season, the NCAA will require that players wear shin guards which meet the standards established by the National Operating Committee on Standards for Athletic Equipment (NOCSAE).” ⁹ The NOCSAE standards should maximize the protective potential of shin guards and should allow for a more accurate interpretation of their prophylactic effect on lower leg injuries. However, size requirements that standardize the required length and width of the guards to match each player's lower leg may still need to be considered.

Addressing the high frequency of ankle sprains is yet another focus for preventive efforts. Ekstrand and Tropp ¹⁷ found that more than half of ankle injuries occurred in players who had previous ankle sprains. Although the repetitive nature of lateral ankle sprains allows us to identify those most at risk, evidence of our success in preventing their recurrence is limited, despite substantial research and clinical efforts directed at reducing the incidence of recurrent lateral ankle sprains. Surve et al ¹⁸ and Tropp et al ¹⁹ suggested that the use of rigid ankle orthoses can reduce the rate of recurrent sprains but not the rate of new sprains. Furthermore, soccer players are notoriously opposed to wearing any foot or ankle prophylaxis other than tape due to the tight fit of soccer shoes and the effect an orthosis could have on performance. Other factors such as neuromuscular control also may contribute to ankle sprains and, therefore, may hold potential for injury prevention. Techniques such as balance training have shown some promise in reducing ankle sprain frequency in soccer players with a history of sprains. ¹⁹ As noted in these results and by previous authors, ²⁰ player contact is the most common injury mechanism for ankle injuries in soccer. Therefore, as mentioned above, rules addressing slide tackles and violent charges in general could affect ankle injury rates as well.

An additional focus should be on preventing injuries to the hip and thigh musculature. As organized preseason practices begin, the intensity and duration of activity increase beyond those of even the most rigorous off-season conditioning programs. These activities include repetitive explosive movements of the thigh and hip. Poor muscle conditioning and repetitive explosive movements during preseason practice, following lower activity levels, could cause many of the noncontact thigh and hip muscle injuries. Graduated muscle conditioning programs, focusing on not only general muscle endurance, but also the explosive motions of the hip and thigh, should be initiated during the summer months to minimize these noncontact muscle injuries.

The ISS results and the potential for preventive intervention provide several avenues for future study. First, with the propensity of contact injuries, tracking the type of contact (eg, sliding, jumping) and whether the contact constituted fair or foul play would allow for objective scrutiny of the existing rules, their enforcement, and the consequences (eg, free kick, ejection, suspension) that result. Next, the repetitive nature of ankle sprains and the risk of suffering multiple sprains could be monitored and detailed more closely. Additionally, an accurate estimate of heat-illness risk could be determined by documenting environmental conditions during practices and games and considering an exposure only when the heat indices warrant heightened concern for heat illness. Finally, with the adoption of the strict NOCSAE standards for shin guards, tracking the effect of these standards on lower leg injuries will provide insight into how specific equipment changes affect specific and overall injury rates.

In conclusion, although injury rates in men's collegiate soccer have remained relatively consistent over the past 15 years, the small, nonsignificant decreasing trend may suggest that our injury awareness and preventive efforts may be demonstrating a cumulative positive effect on injury rates. Lower extremity sprains, contusions, and strains were still the most common injuries, and player-to-player contact was the primary cause during games. Future researchers should focus on providing a more detailed description of concussion injury mechanisms and non–time-loss injuries in men's soccer. Our preventive efforts should spotlight the nature of the contact leading to concussions and lower extremity injury, as well as the rules in place to limit the frequency and severity of these injuries.

DISCLAIMER

The conclusions in the Commentary section of this article are those of the Commentary authors and do not necessarily represent the views of the National Collegiate Athletic Association.