This study found that impact with natural grass surface may be associated with greater reporting of concussion symptoms compared with impact with artificial turf in helmeted American football players at the time of initial clinical evaluation. Although more research is needed, for SRCs that involve contact with the ground during practice and/or competitive play, clinicians may need to consider playing surface (natural grass vs artificial turf) as a (possibly modifying) factor in their evaluation of symptoms of concussion.CLINICAL RELEVANCE
INTRODUCTION
Sport-related concussion (SRC), defined as “a traumatic brain injury induced by biomechanical forces” occurring in sport, has received increasing interest among both the medical community and general population.1 Although game regulations and protective equipment have been reformed over time to enhance safety, SRC and its associated symptoms and sequelae remain significant issues. In the acute postinjury setting, athletes may experience transient somatic, cognitive, and/or emotional symptoms. A subset of individuals may develop “persisting symptoms,” which are defined as symptoms that continue beyond the expected time frame of recovery, that is, > 10 to 14 days in adults and >4 weeks in children.1
Injury prevention measures can target modifiable risk factors to mitigate the number, severity, and symptoms of SRC. In American football, modifiable risk factors include both player factors and nonplayer factors. One example of a nonplayer factor is the playing surface. Currently, American football is played on either natural grass or artificial turf. First introduced in the 1960s, artificial turf is a surface composed of synthetic fibers that is intended to resemble natural grass. There are now several generations of artificial turf, and the surface has evolved from short fibers glued directly to a hard surface to long fibers overlying an infill and shock-absorbing pad. The benefit of artificial turf is the surface’s durability and consistency for play, but safety concerns have been raised over its use as a surface in contact sports.2 In fact, a higher number of lower-extremity orthopedic injuries may occur on artificial turf when compared with natural grass, due to the inability of cleats to release from a potentially injurious position on artificial turf.3 Little research has been conducted into the role of playing surfaces in relation to SRC, but it may be important as studies have shown that up to 30% of SRCs result from helmet-to-ground contact in American football, regardless of playing surface.4
O’Leary et al5 conducted a systemic review and meta-analysis to compare the incidence of SRC on natural grass and artificial turf in competitive contact sports. They identified 12 observational studies that directly compared SRC occurring on natural grass with artificial turf and were published between 1999 (cutoff chosen due to significant revisions in artificial turf over time) and 2019. The studies primarily involved male athletes, were conducted in American football, rugby, and soccer players, and included youth, high school, college, and professional levels of play. Overall, they reported a lower rate of “head injury and concussion” and “concussion only” on artificial turf in competitive contact sports. There were 2 American football studies in high school and college athletes, both of which demonstrated fewer concussions on artificial turf.6,7 Similar to the American football studies, the 2 rugby studies also showed fewer concussions on artificial turf.8,9 The 8 soccer studies showed no significant difference in rates of SRC, with only 2 of the studies reporting significant yet contrasting findings. The authors did note limitations related to comparing sports that are inherently different (eg, level of contact) and study heterogeneity (eg, level of play).
Given that playing surface may be a factor in concussion incidence, it is reasonable to consider that playing surface may be a mitigating factor in severity of helmet-to-ground SRC. The aim of our study was to examine a potential relationship between SRC and playing surface. Specifically, we compared postconcussive symptoms after SRC on natural grass and artificial turf in young American football players. We hypothesized that the severity and number of postconcussive symptoms would be higher after SRC on natural grass compared with artificial turf. To our knowledge, this is the first study to examine reported postconcussive symptoms as they relate to playing surface.
METHODS
Study Population and Participants
Participants were selected from the North Texas Concussion Registry (ConTex), a prospective, longitudinal, multi-institutional collaboration of specialty concussion clinics, which employs a standardized multimodal approach to study risk factors, injury characteristics, and clinical outcomes of concussion.10 The sample for our study drawn from ConTex included participants who were (1) male, (2) aged 10 to 24 years, (3) sustained a helmet-to-ground concussion while playing American football, and (4) presented to a specialty concussion clinic within 14 days of injury. The University of Texas Southwestern Medical Center Institutional Review Board provided approval for participating sites, and written informed consent was obtained from all subjects. For participants younger than 18 years, assent was obtained along with informed consent of the parent/legal guardian for enrollment in the study. Study data were collected and managed using REDCap electronic data capture tools hosted at the University of Texas Southwestern Medical Center. REDCap (Research Electronic Data Capture) is a secure, Web-based software platform designed to support data capture for research studies, providing (1) an intuitive interface for validated data capture; (2) audit trails for tracking data manipulation and export procedures; (3) automated export procedures for seamless data downloads to common statistical packages; and (4) procedures for data integration and interoperability with external sources.11,12
Procedures and Measures
After obtaining informed consent, the following variables were collected at initial specialty clinic visit: sex, age, and time since injury. Participants’ history of headache, history of concussion, number of previous concussions, injury setting (grass vs artificial turf), and postconcussive symptoms were provided by self-report questionnaires in a clinical interview.
Outcome Measures
The primary outcome measure was self-reported postinjury symptoms, which was collected using the Sport Concussion Assessment Tool 5th Edition (SCAT5) Symptom Evaluation that includes 22 items that are rated by the participant as zero (none) to 6 (severe).13 Symptoms are recorded as overall symptom severity score (out of 132) and total number of symptoms (out of 22). Although the Child SCAT5 is available for patients between 5 and 12 years, we used the SCAT5 for all participants regardless of age to standardize data collection and comparisons; previous studies have used parental observation for verification of SCAT5 symptom scores in those younger than 12 years.14
Independent Variable
The independent variable was the type of playing surface on which the participant’s head struck: natural grass versus artificial turf as reported by the participant.
Statistical Analysis
Dichotomous variables were analyzed with appropriate tests; history of headache and absence/presence of symptoms were analyzed with χ2 or Fisher exact test, history of concussion was analyzed with χ2 test, and number of previous concussions was analyzed with Fisher–Freeman–Halton exact test. Continuous variables, including age, time since injury, symptom severity score, and total number of symptoms, were analyzed with independent samples t-tests using pooled or nonpooled variances, as appropriate.
RESULTS
Demographics
A total of 62 participants met inclusion criteria for this study, with 33 participants in the natural grass group and 29 participants in the artificial turf group. The natural grass and artificial turf groups were similar in mean time since injury in days (mean 6.1 vs 5.3 days, P = 0.392), history of headache (Fisher exact test P = 0.312), history of concussion (P = 0.780), and number of previous concussions (Fisher–Freeman–Halton exact test P = 0.876). The groups did differ in age, with the artificial turf group (mean 14.6 years) being older than the natural grass group (mean 13.6 years, t test P = 0.039). These findings are reported in Table 1.
Participant Demographics, Preinjury Characteristics, and Postinjury Data
| Variable | Natural Grass (n = 33) | Artificial Turf (n = 29) |
P |
| Age, yrs (SD) | 13.6 (2.2) | 14.6 (1.6) | 0.039 |
| Time since injury, d (SD) | 6.1 (3.8) | 5.3 (3.2) | 0.392 |
| History of headache, N (%) | 7 (21.2) | 3 (10.3) | 0.312 |
| History of concussion, N (%) | 8 (24.2) | 8 (27.6) | 0.780 |
| Number of previous concussions, N (%) | |||
| 0 | 25 (75.8) | 21 (72.4) | 0.876* |
| 1 | 8 (24.2) | 7 (24.1) | |
| 2 | 0 (0) | 1 (3.4) | |
| SCAT5 symptom severity scores M (SD) | 26.6 (25.5) | 11.6 (13.5) | 0.005 |
| Total number of endorsed SCAT5 symptoms M (SD) | 10.3 (7.2) | 5.9 (5.2) | 0.006 |
P values t test unless otherwise noted.
*Fisher–Freeman–Halton exact test.
Reported Concussion Symptoms
Participants who sustained a SRC on natural grass reported significantly higher mean symptom severity scores compared with those who sustained a SRC on artificial turf (mean 26.6, SD = 25.5 vs mean 11.6, SD = 13.50; t test P = 0.005). Furthermore, participants who sustained a SRC on natural grass reported significantly higher total number of symptoms compared with those who sustained a SRC on artificial turf (mean 10.3, SD = 7.2 vs mean 5.9, SD = 5.2; t test P = 0.006). These findings are depicted in Figure 1.
Comparison of severity and number of reported symptoms on the sport concussion assessment tool 5th edition SCAT5 symptom evaluation at the time of initial evaluation. Initial evaluation ≤14 days postinjury.
Specific Symptoms
The absence or presence of specific symptoms on the SCAT5 Symptom Evaluation were also compared between the 2 groups. The probability of 7 individual symptoms were found to be higher after a SRC on natural grass compared with artificial turf: dizziness (P P P = 0.027), feeling “in a fog” (P = 0.009), difficulty remembering (P = 0.004), fatigue or low energy (P = 0.024), and confusion (P = 0.031). These findings are reported in Table 2.
Number and Percentages of Participants Reporting Symptoms on the SCAT5 Symptom Evaluation
| Symptom | Natural Grass (n = 33) n (%) |
Artificial Turf (n = 29) n (%) |
P |
| Headache | 25 (75.8) | 17 (58.6) | 0.150 |
| “Pressure in head” | 17 (51.5) | 13 (44.8) | 0.599 |
| Neck pain | 14 (42.4) | 7 (24.1) | 0.129 |
| Nausea or vomiting | 9 (27.3) | 3 (10.3) | 0.092 |
| Dizziness | 17 (51.5) | 3 (10.3) | |
| Blurred vision | 15 (45.5) | 1 (3.4) | |
| Balance problems | 15 (45.5) | 9 (31.0) | 0.245 |
| Sensitivity to light | 17 (51.5) | 9 (31.0) | 0.103 |
| Sensitivity to noise | 17 (51.1) | 7 (24.1) | 0.027 |
| Feeling slowed down | 16 (48.5) | 9 (31.0) | 0.162 |
| Feeling like “in a fog” | 16 (48.5) | 5 (17.2) | 0.009 |
| “Don’t feel right” | 18 (54.5) | 13 (44.8) | 0.445 |
| Difficulty concentrating | 18 (54.5) | 15 (51.7) | 0.824 |
| Difficulty remembering | 20 (60.6) | 7 (24.1) | 0.004 |
| Fatigue or low energy | 22 (66.7) | 11 (37.9) | 0.024 |
| Confusion | 11 (33.3) | 3 (10.3) | 0.031 |
| Drowsiness | 19 (57.6) | 10 (34.5) | 0.069 |
| More emotional | 8 (24.2) | 4 (13.8) | 0.299 |
| Irritability | 15 (45.5) | 11 (37.9) | 0.549 |
| Sadness | 7 (21.2) | 1 (3.4) | 0.057* |
| Nervous or anxious | 10 (30.3) | 4 (13.8) | 0.121 |
| Trouble falling asleep | 15 (45.5) | 8 (27.6) | 0.146 |
All other P values are the result of χ2 analyses.
*Fisher exact test.
DISCUSSION
To better understand a potential relationship between SRC and playing surface, we compared postconcussive symptoms following SRC on natural grass and artificial turf in young American football players. Participants who sustained a SRC on natural grass reported higher symptom severity scores and higher total number of symptoms compared with those who sustained a SRC on artificial turf. Furthermore, 7 symptoms were more likely to be present after SRC on grass, including dizziness, blurred vision, sensitivity to noise, feeling “in a fog,” difficulty remembering, fatigue or low energy, and confusion.
Although SRC and postconcussive symptoms have been studied in relation to other injury-related characteristics, such as loss of consciousness, posttraumatic amnesia, and delayed removal from play,15 this is the first study to our knowledge to investigate reported postconcussive symptoms as they relate to playing surface. Reported postconcussive symptoms are important because the severity of acute/subacute symptoms is the strongest predictor of slower recovery after SRC.1 In addition, any relationship between symptoms and playing surface is important because playing surface is a potentially modifiable factor that does not require player participation, although more work in this area is needed. In addition to these potentially important clinical implications, another strength of our study is similarity of the groups being compared with respect to their history of headache, concussion, and number of previous concussions. Finally, previous studies compared the incidence of SRC on natural grass versus artificial turf but did not delineate actual mechanism of injury; thus, helmet-to-helmet, helmet-to-player, and helmet-to-ground injuries were all included. This study included only SRCs that resulted from helmet-to-ground contact, which may provide more specific information about a potential relationship between SRC/postconcussive symptoms and playing surface.
There are also limitations to consider in our pilot investigation, including our relatively small sample size and the wide range of symptom scores that were seen, although this was true for both the groups. Another possible limitation of the study is the small but statistically significant difference in age between the 2 groups because the mean age of the artificial turf group was higher by 1 year. This may be a reflection that older higher-level athletes are more likely to play on artificial turf; however, it is possible that this reflects a protective effect of older age and more football experience. There were also potential confounding variables that could not be accounted for in this study, including the condition of the playing surface. For example, with regard to artificial turf, we could not account for the generation, type, age, nature, and maintenance of the playing surface. It remains unknown whether these factors affect SRC, but presumably, older generation, older age, different composition/density, and poor maintenance may provide a less optimal playing surface for performance and injury prevention. Similarly, natural grass also varies from patchy to well manicured in texture, in addition to how level or muddy it may be in any particular setting or season. Another factor that could not be accounted for in this study was whether the SRC occurred during practice or game; it is possible that the level of competition may affect SRC and postconcussive symptoms.
This was a pilot study that investigated SRCs occurring in only male participants in 1 sport. At this time, these preliminary findings do not support the relative safety of one playing surface over another; it showed only that the playing surface may be a mitigating factor in our study population. However, these findings taken together with ones previously reported showed lower incidence of SRC on artificial turf compared with natural grass in competitive contact sports,5 suggesting that additional research is warranted to further investigate a potential relationship between SRC/postconcussive symptoms and playing surface. Although this study compared postconcussive symptoms reported at 1 time point within 14 days of injury, future directions for research may include comparing recovery between those who sustained a SRC on natural grass and artificial turf and in larger samples. In addition to evaluating early reported symptoms as in this study, it would be useful to elucidate whether playing surface has an association with different rates and degrees of recovery over time across different levels of play in different sports.
ACKNOWLEDGMENTS
The authors wish to thank the cooperating institutions in the North Texas Concussion Registry: UT Southwestern Medical Center, Texas Scottish Rite Hospital for Children, Children’s Medical Center Dallas, and Texas Health Resources. Assistance in the development of this manuscript was provided by Sarah Sprinkle, M.A.
References