Influence of Extrinsic Risk Factors on National Football League Injury Rates

Interaction of Surface Type, Temperature, and Week of Season on Concussion Risk in the National Football League: A Bayesian Analysis

BACKGROUND

Artificial turf fields and environmental conditions may influence sports concussion risk, but existing research is limited by uncontrolled confounding factors, limited sample size, and the assumption that risk factors are independent of one another. The purpose of this study was to examine how playing surface, time of season, and game temperature relate to diagnosed concussion risk in the National Football League (NFL).

METHODS

This retrospective cohort study examined data from the 2012 to the 2019 NFL regular season. We fit Bayesian negative binomial regression models to relate how playing surface, game temperature, and week of the season independently related to diagnosed concussion risk and any interactions among these factors.

RESULTS

We identified 1096 diagnosed concussions in 1830 games. There was a >99% probability that concussion risk was reduced on grass surface (median incidence rate ratio [IRR] = 0.78 [95% credible interval: 0.68, 0.89]), >99% probability that concussion risk was lower at higher temperatures (IRR = 0.85 [0.76,0.95] for each 7.9 °C), and >91% probability that concussion risk increased with each week of the season (IRR = 1.02 [1.00,1.04]). There was an >84% probability for a surface × temperature interaction (IRR = 1.01 [0.96, 1.28]) and >75% probability for a surface × week interaction (IRR = 1.02 [0.99, 1.05]).

CONCLUSIONS

Diagnosed concussion risk is increased on artificial turf compared with natural grass, and this is exacerbated in cold weather and, independently, later in the season. The complex interplay between these factors necessitates accounting for multiple factors and their interactions when investigating sports injury risk factors and devising mitigation methods.

Association of Injury Rates Among Players in the National Football League With Playoff Qualification, Travel Distance, Game Timing, and the Addition of Another Game: Data From the 2017 to 2022 Seasons

Background

Injury incidence is higher in the National Football League (NFL) than in other collision sports. Although previous research has identified that scheduling variations, including overseas games and bye week timing, does not affect concussion risk, data are currently lacking regarding the effects of scheduling variation on season-long musculoskeletal injury incidence.

Purpose

To determine whether higher cumulative travel distance, overseas play, an early season bye week, and an expansion of the regular season is associated with higher injury rates in the NFL.

Study Design

Descriptive epidemiology study.

Methods

All 1275 injuries across 5 NFL seasons from 2017 to 2018 through 2021 to 2022 were reviewed retrospectively. Injury data and travel distances were extracted from publicly available sources, which were cross-referenced for validation. Injury rates were calculated per 1000 athletic-exposures (AEs). Cumulative team travel distances were compared statistically using a linear regression. Single factor analysis of variance was used to compare categorical variables.

Results

Travel distance did not significantly predict injury rates (P = .47), and there was no difference in injury rates between teams that played a game overseas versus teams that did not (19.3 injuries per 1000 AEs for both; P = .96). In addition, no difference was found in injury rates (F[109,2100[ = 0.704; P = .73) or players placed on the injured reserve list (F[99,778] = 1.70; P = .077) between various bye weeks (P = .73). Injury rates did not differ between the new 17-game regular season (18.4 per 1000 AEs) versus the previous four 16-game regular seasons (19.7 per 1000 AEs; P = .12). However, teams that did not qualify for the playoffs had a significantly higher injury rate (19.9 per 1000 AEs) as well as players on injured reserve (8.0 per 1000 AEs) than playoff-qualifying teams (18.4 and 6.8 per 1000 AEs, respectively; P < .05 for both).

Conclusion

Over 5 NFL seasons, cumulative travel distance, overseas play, bye week timing, and adding 1 regular season game were not associated with increased injury rates in NFL players. However, a lack of regular season success was associated with higher injury rates and more players on injured reserve.

Validity of Research Based on Publicly Obtained Data in Sports Medicine: A Quantitative Assessment of Concussions in the National Football League

CONTEXT

Numerous researchers have leveraged publicly available internet sources to publish clinical research concerning incidence and recovery from injuries in National Football League (NFL) players.

OBJECTIVE

This study aims to (1) provide a comprehensive systematic review of all publicly obtained data studies (PODS) regarding concussions in NFL athletes and (2) quantify the percentage of injuries identified by these studies in comparison with published concussion data from the NFL injury database.

STUDY SELECTION

A systematic review was conducted in accordance with PRISMA guidelines to identify all published studies utilizing publicly obtained data regarding concussions in NFL athletes.

STUDY DESIGN

Systematic review.

LEVEL OF EVIDENCE

Level 4.

DATA EXTRACTION

Manuscript details, factors related to the athletes of interest (eg, study period, positions included), and results (eg, concussion rate, number of total concussions, return-to-play data) were extracted independently by 2 authors. Results were compared with incident concussions reported from 2015 to 2019 by each medical staff member to the NFL database linked to the League's electronic health record (EHR).

RESULTS

A total of 20 concussion-focused manuscripts based on PODS were identified from 2014 to 2020. PODS captured between 20% and 90% of concussions (mean, 70%) reported by medical staff to the injury database. PODS reported that 55% of concussions occurred on offensive plays, 45% on defensive plays and <1% occurred during special teams plays, compared with 44%, 37%, and 18%, respectively, as indicated by published data from the NFL injury database. When analyzed by position groups, running backs and quarterbacks comprised the most over-represented positions concussed in PODS, while offensive linemen, defensive backs, and linebackers comprised the most under-represented positions.

CONCLUSION

PODS captured approximately 70% of concussions reported by NFL medical staff to the NFL injury database. There is heterogeneity in the degree to which PODS were able to identify concussions, with a bias toward concussions among players at higher profile positions.

Risk factors for hamstring strain injury in male college American football players -a preliminary prospective cohort study

BACKGROUND

Given the frequency of hamstring strain injuries (HSI) among male college American football players, several studies have attempted to determine whether certain risk factors can predict their occurrence. However, no consensus on modifiable risk factors for HSIs in male college American football players has yet been reached to prevent these injuries. This study aimed to clarify risk factors for HSI prospectively in college male American football players.

METHODS

A total of 78 male college American football players, whose positions were limited to skill positions, were medically assessed for potential risk factors of HSI. The preseason medical assessment included anthropometric measurements, joint laxity and flexibility, muscle flexibility, muscle strength, and balance ability.

RESULTS

HSI occurred in a total of 25 thighs from 25 players (32.1%). Injured players had significantly lower hamstring flexibility (p = 0.02) and hamstring to quadriceps strength ratio (H/Q) (p = 0.047) compared to uninjured players. Additionally, injured players had significantly lower general joint laxity scores, especially for the total (p = 0.04), hip (p = 0.007), and elbow (p = 0.04) scores, compared to uninjured players.

CONCLUSIONS

Lower hamstring flexibility, lower hamstring to quadriceps strength ratio, and lower general joint laxity score were identified as risk factors for HSI in male college American football players placed in skill positions. The muscle flexibility and H/Q ratio could be useful in preventing HSI in such players.

Lisfranc injury: Prevalence and maintaining a high index of suspicion for optimal evaluation

OBJECTIVES

To quantify the long-term prevalence of game-related Lisfranc trauma in college football on artificial turf and natural grass.

METHODS

32 universities were evaluated over 10 competitive seasons across all Football Bowl Subdivision (FBS) conferences. Outcomes of interest included injury severity, injury category, primary type of injury, player and skill position, injury mechanism and situation, elective imaging and surgical procedures, and field conditions. Injury incidence rates (IIR) were calculated using injuries per 10 games = (number of injuries) number of games) × 10.

RESULTS

Of the 1577 games documented, 783 games (49.7%) were played on a 3-layer artificial turf (≥9.0 lbs/ft²) infill system versus 794 games (50.3%) played on natural grass. In sum, 78 Lisfranc cases were documented with 34 (43.6%) occurring on artificial turf, and 44 (56.4%) on natural grass. MANOVAs indicated significant main effects by injury category (F_3,74 = 6.439; P = .001), and injury mechanism (F_5,72 = 3.372; P = .009) observed between surfaces, but not by injury severity (F_2,75 = 0.720; P = .490), primary type of injury (F_4,73 = 0.772; P = .547), overall player (F_2,75 = 0.219; P = .804) and skill positions (F_8,69 = 0.850; P = .563), injury situation (F_10,67 = 1.030; P = .428), elective imaging and surgical procedures (F_3,74 = 0.515; P = .673), or field conditions (F_2,75 = 0.375; P = .688). Post hoc analyses indicated significantly greater incidences (P < .05) of Lisfranc trauma on natural grass attributed to shoe:surface interaction during noncontact play, and during no contact, foot rotation or planting. Ligament tears (n = 8; 57.1%), with minimal cases of subluxation/dislocations (n = 4; 28.6%) and fractures (n = 2; 14.3%) comprised grade 3 cases across both surfaces.

CONCLUSION

In regards to Lisfranc trauma, a 3-layer, heavyweight artificial infill surface is as safe or safer than natural grass. The findings of this study may be generalizable only to this level of football competition.

Bad Altitude: Categorizing Elevation Produces Spurious Association With Concussions in the National Football League (NFL)

OBJECTIVE: To assess whether prior analyses, where there was a relationship between altitude and concussion rates in American football, would replicate using a larger data set and altitude as a continuous variable. DESIGN: Cohort study replication. METHODS: We analyzed data from all NFL regular season games from 2012-2019. Concussions were identified from public databases and NFL injury reports. The altitude of each stadium was identified using mapping software. Concussion rates were calculated for each stadium and plotted against continuous altitude. We calculated crude rate ratios for several categorical cut points and used logistic and Poisson regression models to assess associations with continuous altitudes. RESULTS: We identified 867 players (1103 player seasons) who sustained 1159 concussions during the time period 2012-2019. All continuous plots and models showed no evidence of any association between concussions and altitude. A Poisson model found an IRR of 1.00 (95% CI, 0.99-1.01) for every 100-ft increase in altitude. A 644-ft cut point (used in previous studies) produced a significant difference (incidence rate ratio [IRR], 0.71; 95% CI, 0.54-0.94) in 2012-2013, but this did not replicate in 2014-2019 (IRR, 0.99; 95% CI, 0.84-1.14). CONCLUSION: We found no association between altitude and concussion rates in the NFL when altitude was analyzed continuously rather than inappropriately categorized. Our findings should increase skepticism of any effect of altitude on concussions at the elevations at which most American football is played, as well as clinical interventions based on that theory. It also underscores the importance of keeping continuous variables continuous wherever possible. J Orthop Sports Phys Ther 2022;52(10):694-701. Epub: 27 July 2022. doi:10.2519/jospt.2022.11220.

Influence of Preseason Versus In-Season Play on Achilles Tendon Injuries in the National Football League

Background:

A ruptured Achilles tendon (AT) can sideline a player for 6 to 12 months and reduce their power rankings by more than 50%. Previous research has compared AT rupture rates in different game conditions.

Purpose:

To determine environmental and physiological risk factors for AT tears, given the minimal amount of research on AT ruptures in the National Football League (NFL).

Study Design:

Case series; Level of evidence, 4.

Methods:

NFL players with a diagnosed AT tear between 2009 and 2016 were selected as the study population for this retrospective analysis. Data on NFL injury were collected from an established database composed of publicly available information. Player profiles were employed to determine position, team, and game statistics at the time of injury. The proportion of NFL rookies was approximated by summing the number of draft picks and the number of signed, undrafted free agents and measured against the number of roster spots before the season.

Results:

Between 2009 and 2016, there were 101 documented AT tears. Of these, 64% (65/101) occurred before the official season, including preseason games. Of the 36 tears that occurred in-season, 34 were during games. Overall, 29% (19/65) of the preseason tears occurred in rookies and 100% (36/36) of the in-season tears affected nonrookies. Of the rookies with AT ruptures, 42.11% returned to play in the NFL, while 62.20% of the nonrookies came back to partake in future seasons. Despite an average age of 26.7 years, the tear distribution was bimodal with players aged 24 and 36 years exhibiting the highest rates of tear.

Conclusion:

In our review of AT tears in NFL athletes, a large percentage of the tears occurred in rookie players, especially during the preseason. We also found that tears during the season occurred in only nonrookies, suggesting that the preseason is when rookies experience the greatest risk for injury.

Head Games: A Systematic Review and Meta-analysis Examining Concussion and Head Impact Incidence Rates, Modifiable Risk Factors, and Prevention Strategies in Youth Tackle Football

OBJECTIVES

The aims were to (1) examine the rates and mechanisms of concussion and head impact in youth football (high school level or younger); (2) identify modifiable risk factors for concussion and head impact; and (3) evaluate the effectiveness of prevention strategies in tackle football at any level.

METHODS

Nine databases (CINAHL Plus with Full Text; Cochrane Central Register of Controlled Trials; EMBASE; ERIC; Ovid MEDLINE(R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations and Daily; ProQuest Dissertations & Theses Global Database; PsycINFO; Scopus; and SPORTDiscus with Full Text) were searched using the search strategy focusing on four main concepts: concussion/head impact, tackle football, modifiable risk factors, and primary prevention. Two reviewers completed title, abstract, and full-text screening as well as risk of bias assessment (using the Downs and Black checklist), with a third author available to resolve any disagreements.

MAIN RESULTS

After removing duplicates, 1911 articles were returned. Fifty-eight articles were included in the review and 20 in the meta-analysis. The overall combined rates of concussion (including game and practice-related concussion) based on the meta-analysis were 0.78 concussions/1000 athlete exposures [95% confidence interval (CI) 0.67-0.89] for high school football (ages 13-19) and 1.15 concussions/1000 athlete exposures (95% CI 0.89-1.41) for minor football players (ages 5-15). There is evidence that contact training and practice contact restrictions have reduced the rate of head impacts and concussion. Heads Up Football (an intervention focused on coach education and contact training) has been shown to reduce the rate of concussion by 32% and head impacts by 38% amongst high school football players. Limiting contact practices in high schools to 2 days per week reduced practice head impacts per player-season by 42%, and limiting full contact in practice to 75 min per week in the second week of the season and 60 min in week 3 and beyond resulted in a 54% decrease in the practice-related concussion rate (p = 0.003).

CONCLUSIONS

This review identified a critical need for interventions to address the high rates of concussion and head impact in youth football. To date, contact training and contact restrictions have the strongest evidence supporting their effectiveness at reducing these rates. Future research should use consistent concussion definitions and validated injury surveillance systems, and ensure complete reporting of participant characteristics and sampling details. Prospero ID CRD42020193775.

The Effect of Thursday Night Games on In-Game Injury Rates in the National Football League

BACKGROUND

Although claims of increased injury rates with Thursday night National Football League (NFL) games exist, a paucity of data exist substantiating these claims.

PURPOSE

To evaluate the effect of rest between games on in-game injury rates as it pertains to overall injury incidence, location, and player position.

STUDY DESIGN

Descriptive epidemiologic study.

METHODS

Data were obtained from official NFL game books for regular season games from all 32 teams for the 2013-2016 seasons. All in-game injuries recorded in official game books were included. Rest periods between games were classified as short (4 days), regular (6-8 days), or long (≥10 days). Overall observed injury rates per team-game were analyzed in relation to different rest periods using negative binomial regression. For results with significant overall findings, pairwise comparisons were tested using the Wald chi-square test. Exploratory secondary analyses were performed in a similar fashion to assess differences in injury rates for the different rest periods when stratified by anatomic location and player position.

RESULTS

A total of 2846 injuries were identified throughout the 4 seasons. There was an overall significant difference in injuries per team-game between short, regular, and long rest (P = .01). With short rest, an observed mean of 1.26 injuries per game (95% CI, 1.06-1.49) was significantly different from the 1.53 observed injuries per game with regular rest (95% CI, 1.46-1.60; P = .03), but not compared with the 1.34 observed injuries per game with long rest (P = .56). For player position, only the tight end, linebacker, and fullback group demonstrated significant differences between the injury rates for different rest categories. Quarterback was the only position with more injuries during games played on Thursday compared with both regular and long rest. This specific analysis was underpowered and the difference was not significant (P = .08). No differences were found regarding injury rates in correlation with differences in rest periods with different injury locations.

CONCLUSION

A short rest period between games is not associated with increased rates of observed injuries reported in NFL game books; rather, our data suggest there are significantly fewer injuries for Thursday night games compared with games played on regular rest. Future research correlating rest and quarterback injury rates is warranted.

Recalibrating the risk of hamstring strain injury (HSI): A 2020 systematic review and meta-analysis of risk factors for index and recurrent hamstring strain injury in sport

OBJECTIVE

To systematically review risk factors for hamstring strain injury (HSI).

DESIGN

Systematic review update.

DATA SOURCES

Database searches: (1) inception to 2011 (original), and (2) 2011 to December 2018 (update). Citation tracking, manual reference and ahead of press searches.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies presenting prospective data evaluating factors associated with the risk of index and/or recurrent HSI.

METHOD

Search result screening and risk of bias assessment. A best evidence synthesis for each factor and meta-analysis, where possible, to determine the association with risk of HSI.

RESULTS

The 78 studies captured 8,319 total HSIs, including 967 recurrences, in 71,324 athletes. Older age (standardised mean difference=1.6, p=0.002), any history of HSI (risk ratio (RR)=2.7, p<0.001), a recent HSI (RR=4.8, p<0.001), previous anterior cruciate ligament (ACL) injury (RR=1.7, p=0.002) and previous calf strain injury (RR=1.5, p<0.001) were significant risk factors for HSI. From the best evidence synthesis, factors relating to sports performance and match play, running and hamstring strength were most consistently associated with HSI risk. The risk of recurrent HSI is best evaluated using clinical data and not the MRI characteristics of the index injury.

SUMMARY/CONCLUSION

Older age and a history of HSI are the strongest risk factors for HSI. Future research may be directed towards exploring the interaction of risk factors and how these relationships fluctuate over time given the occurrence of index and recurrent HSI in sport is multifactorial.

The Effect of Game Importance on Concussion Incidence in the National Football League: An Observational Study

Introduction Concussion incidence in the National Football League (NFL) has been shown to generally increase as the season progresses. Yet, there is evidence that suggests that the incidence stagnates or decreases in the final quarter of the season in comparison to the third quarter. This anomaly cannot be explained by any of the known modulators of concussion incidence. However, the fact that the teams start getting eliminated from playoff contention in the fourth quarter of the season may explain this pattern in concussion incidence. This study tests whether there is a difference in concussion incidence in games between teams who are still in the playoff hunt [in the hunt (IH) games] versus games where both teams have had their playoff fate already determined (non-IH games). Methods We obtained details of 166 documented concussions from weeks 13-16 of each of the four NFL seasons from 2012 to 2015 from Public Broadcasting Service's (PBS) Frontline Concussion Watch and matched them to the games in which they occurred. Each game was categorized based on the playoff status [clinched (CL), eliminated (EL), or IH] of the teams playing in the game. Concussion incidence of the game types was compared to each other using a one-way analysis of variance (ANOVA) test and student t-tests. Additionally, concussion incidences at six different player positions in important games were compared to the corresponding incidences in unimportant games. An ordinary least squares regression was used to examine the effects of game importance and plays per game on concussion incidence. Results Concussion incidence in important games (mean = 0.651 ±0.055) did not differ significantly (p: 0.890) from the incidence in unimportant games (mean = 0.623 ±0.143). Instead, plays per game was found to be the primary driver of concussion in the regression analysis (β = 0.01605; p: 0.025). At the position-specific level, running backs (RB) were the only position to demonstrate a significant increase in concussion incidence (p: 0.004) in important games (mean = 0.049 ±0.017) compared to unimportant games (mean = 0.00 ±0.00). Conclusions The results suggest that, in general, players are not more likely to suffer concussions in IH games than in non-IH games. However, RBs may have an increased risk of concussion in games with playoff implications than in games without.

A Systematic Review of the Orthopaedic Literature Involving National Football League Players

Background

Orthopaedic injuries of National Football League (NFL) players can have a deleterious effect on their health, with minimal to no high-level evidence on the management of these injuries.

Purpose

To summarize all data published between January 1980 and March 2018 on orthopaedic injuries experienced by NFL candidates and professional players in the NFL.

Study Design

Systematic review; Level of evidence, 4.

Methods

A literature search of studies examining orthopaedic injuries in the NFL was performed through the PubMed, Embase, and CINAHL databases. The review included studies of orthopaedic injuries in college football recruits attending the NFL Combine as well as professional NFL players. Excluded were studies of nonorthopaedic injuries, such as concussions, traumatic brain injury, facial injuries, and vascular injuries, as well as case reports.

Results

A total of 147 articles met the inclusion criteria and were divided into 11 topics based on anatomic site: general (16%), spine (13%), shoulder (13%), elbow (3%), hand and wrist (3%), trunk (0.7%), hip and pelvis (7%), thigh (3%), knee (24%), ankle (5%), and foot (12%). Of these studies, 74% were of level 4 evidence. Most studies obtained data from the NFL Combine database (26%), by searching the internet (24%), and via the NFL Injury Surveillance System (22%). Studies using internet search methods to identify injuries consistently found fewer participants than studies using the NFL Injury Surveillance System.

Conclusion

This systematic review provides National Collegiate Athletic Association and NFL team physicians with a single source of the most current literature regarding orthopaedic injuries in NFL players. Most research was published on knee, spine, shoulder, and foot injuries and consisted of level 4 evidence. A substantial portion of the published literature was based on data obtained from internet searches and may not accurately represent the NFL population.

Incidence, Mechanisms, and Severity of Game-Related High School Football Injuries Across Artificial Turf Systems of Various Infill Weights

Background:

Artificial turf surfaces are developed to duplicate playing characteristics of natural grass. With the newer generations of sand and rubber infill systems, the infill is a common component that varies between fields and is a critical factor that could influence the player-surface interaction. Because the influence of infill weight on sport trauma is unknown, this study quantified football trauma in high schools in the United States across artificial turf systems of various infill weights.

Hypothesis:

Athletes would not experience differences in game-related injuries across artificial turf systems of various infill weights.

Study Design:

Cohort study; Level of evidence, 2.

Methods:

Artificial turf systems were divided into 4 sand/rubber infill weight groups by pounds per square foot: ≥9.0, 6.0-8.9, 3.0-5.9, and 0.0-2.9. A total of 57 high schools in 4 states participated over the course of 5 seasons. Outcomes of interest included injury severity, as a function of infill weight, across head, knee, and shoulder traumas; injury category; primary type of injury; tissue type; specific body location of injury; cleat design; environmental factors; and turf age. Data were subject to multivariate analyses of variance (MANOVAs) and Wilks λ criteria through use of general linear model procedures.

Results:

Of 1837 games documented, 528 games were played on infill weights of ≥9.0 lb/ft², 521 on 6.0-8.9 lb/ft², 525 on 3.0-5.9 lb/ft², and 263 on 0.0-2.9 lb/ft², with 4655 total injuries reported. MANOVAs indicated significant infill weight effects across injury severity (F_2,4648 = 5.087; P = .0001), with significant main effects also observed by injury category, tissue injured, lower extremity joint and muscle, cleat design, environmental factors, and turf age. Post hoc analyses indicated significantly lower (P < .05 to .0001) total and substantial traumas, concussions, shoe-surface interaction during contact trauma, surface impacts, muscle-tendon overload, cleat design influence, adverse weather trauma, lower extremity injuries, and turf age effect while athletes were competing on the 6.0 to ≥9.0 lb/ft² infill weight systems compared with the lighter infill weight systems.

Conclusion:

As infill surface weight decreased, football trauma significantly increased across numerous playing conditions. Based on findings, high school football fields should minimally contain 6.0 pounds of infill per square foot.

National Rugby League match scheduling and rate of concussion

OBJECTIVES

The aims of this study were to evaluate the relationship between pre-match rest days, match location, time of season, and match outcome with diagnosed concussion and use of the Concussion Interchange Rule (CIR) during the 2014 NRL season.

DESIGN

Descriptive observational study.

METHODS

This study reviewed all instances of diagnosed concussions, CIR activations, and match characteristics during the 2014 NRL season. Information pertaining to the use of the CIR was obtained from the league. Each club provided information of diagnosed concussion.

RESULTS

A total of 402 NRL games were analyzed, the concussion interchange rule was activated 167 times, and 60 concussions were diagnosed in 53 of the matches. A significantly greater proportion of concussions occurred during the first match of the season (38% vs. 15% of in-season matches; p=0.02). Days of rest, match location, season stage, and match outcome were not associated with a higher proportion of concussions. Furthermore, we did not detect a significant association between CIR activation and days of rest prior to the match, opponent rest prior to the match, match location, round of the season, or match outcome.

CONCLUSIONS

A significantly greater proportion of concussions were diagnosed during the first match of the season. Days between matches, opponent days of rest, match location, or other rounds (aside from round 1) of the season were not associated with CIR activation or diagnosed concussion. Varied game scheduling during the season does not appear to be associated with increased risk for concussion or use of the CIR in the NRL.

Higher Rates of Lower Extremity Injury on Synthetic Turf Compared With Natural Turf Among National Football League Athletes: Epidemiologic Confirmation of a Biomechanical Hypothesis

BACKGROUND

Biomechanical studies have shown that synthetic turf surfaces do not release cleats as readily as natural turf, and it has been hypothesized that concomitant increased loading on the foot contributes to the incidence of lower body injuries. This study evaluates this hypothesis from an epidemiologic perspective, examining whether the lower extremity injury rate in National Football League (NFL) games is greater on contemporary synthetic turfs as compared with natural surfaces.

HYPOTHESIS

Incidence of lower body injury is higher on synthetic turf than on natural turf among elite NFL athletes playing on modern-generation surfaces.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

Lower extremity injuries reported during 2012-2016 regular season games were included, with all 32 NFL teams reporting injuries under mandated, consistent data collection guidelines. Poisson models were used to construct crude and adjusted incidence rate ratios (IRRs) to estimate the influence of surface type on lower body injury groupings (all lower extremity, knee, ankle/foot) for any injury reported as causing a player to miss football participation as well as injuries resulting in ≥8 days missed. A secondary analysis was performed on noncontact/surface contact injuries.

RESULTS

Play on synthetic turf resulted in a 16% increase in lower extremity injuries per play than that on natural turf (IRR, 1.16; 95% CI, 1.10-1.23). This association between synthetic turf and injury remained when injuries were restricted to those that resulted in ≥8 days missed, as well as when categorizations were narrowed to focus on distal injuries anatomically closer to the playing surface (knee, ankle/foot). The higher rate of injury on synthetic turf was notably stronger when injuries were restricted to noncontact/surface contact injuries (IRRs, 1.20-2.03; all statistically significant).

CONCLUSION

These results support the biomechanical mechanism hypothesized and add confidence to the conclusion that synthetic turf surfaces have a causal impact on lower extremity injury.

Does the Environment Influence the Frequency of Concussion Incidence in Professional Football?

Background

Sports-related concussion is a major cause of mild traumatic brain injury (mTBI). It is possible that environmental factors, such as temperature, humidity, and stadium's altitude, may influence the overall incidence of concussions during a game.

Purpose

To examine the impact of environmental factors, such as temperature, humidity, barometric pressure, and dew point, on concussion incidence.

Methods

Public Broadcasting Service (PBS) FRONTLINE Concussion Watch was used to collect injury data on 32 NFL teams during regular season games from 2012 to 2015. Weather data points were collected from Weather Underground. Concussion incidence per game, the probability of a concussion during a game, and a difference in mean game-day temperature, humidity, dew point, and barometric pressure between concussion and concussion-free games were calculated. Our analysis included t-tests, analysis of variance (ANOVA), multivariate correlation tests, and logistic and Poisson regression. 

Results

Overall, 564 concussions were reported. There were 411 games with concussions and 549 games without concussions. We observed a significant decrease in concussion incidence with increasing temperature, both when the temperature was divided into 20^oF increments or into quartiles (p = 0.005 and p = 0.002, respectively). We identified a statistically significant lower mean-game day temperature in concussion games compared to concussion-free games (p < 0.0006). We also observed a significant decrease in the incidence of concussion per game with increasing dew point. There was no significant difference in concussion incidence in barometric pressure and humidity. The logistic regression model predicted a decrease in the probability of a concussion in games with higher temperatures and dew points.

Conclusions

National Football League (NFL) players experienced an increased risk of concussion during football games played in colder temperatures and at lower dew points. Further research on environmental effects on concussions may aid in improving player safety in football leagues.

Game Schedules and Rate of Concussions in the National Football League

Background

Concussion prevention in the National Football League (NFL) is an important priority for player safety. The NFL now has modified game schedules, and one concern is that unconventional game schedules, such as a shortened rest period due to playing on a Thursday rather than during the weekend, may lead to an increased risk of injuries.

Hypothesis

Unconventional game schedules in the NFL are associated with an increased rate of concussion.

Study Design

Descriptive epidemiological study.

Methods

This study analyzed concussions and game schedules over the NFL regular seasons from 2012 to 2015 (4 years). Documented numbers of concussions, identified by use of the online database PBS Frontline Concussion Watch, were summarized by regular-season weeks. Association of days of rest and game location (home, away, or overseas) with the rate of concussion was examined by use of the χ² test. Logistic regression analysis was performed to examine the relationships of days of rest and home/away games to the risk of repeated concussions, with adjustment for player position.

Results

A total of 582 concussions were analyzed in this study. A significantly greater number of concussions occurred in the second half of the season (P < .01). No significant association was found between the rate of concussion and the days of rest, game location, or timing of the bye week by the team or the opponent (P > .05). Game schedules were not significantly associated with the occurrence of repeat concussions (P > .05).

Conclusion

Unconventional game schedules in the NFL, including playing on Thursday and playing overseas, do not seem to put players at increased risk of concussions.

Updated Review of the Applied Physiology of American College Football: Physical Demands, Strength and Conditioning, Nutrition, and Injury Characteristics of America’s Favorite Game

While there are various avenues for performance improvement in college American football (AF), there is no comprehensive evaluation of the collective array of resources around performance, physical conditioning, and injury and training/game characteristics to guide future research and inform practitioners. Accordingly, the aim of the present review was to provide a current examination of these areas in college AF. Recent studies show that there is a wide range of body compositions and strength characteristics between players, which appear to be influenced by playing position, level of play, training history/programming, and time of season. Collectively, game demands may require a combination of upper- and lower-body strength and power production, rapid acceleration (positive and negative), change of direction, high running speed, high-intensity and repetitive collisions, and muscle-strength endurance. These may be affected by the timing of and between-plays and/or coaching style. AF players appear to possess limited nutrition and hydration practices, which may be disadvantageous to performance. AF injuries appear due to a multitude of factors—strength, movement quality, and previous injury—while there is also potential for extrinsic factors such as playing surface type, travel, time of season, playing position, and training load. Future proof-of-concept studies are required to determine the quantification of game demands with regard to game style, type of opposition, and key performance indicators. Moreover, more research is required to understand the efficacy of recovery and nutrition interventions. Finally, the assessment of the relationship between external/internal-load constructs and injury risk is warranted.

Distal Fibula Fractures in National Football League Athletes

Background:

Despite the frequency of distal fibula fractures in elite athletes and the significant potential impact on the athletes’ season and future careers, little data exist characterizing the epidemiology of these injuries or, more importantly, return to competition.

Purpose:

To (1) evaluate the incidence of acute distal fibula fractures in National Football League (NFL) athletes, including isolated distal fibula and combined ankle fracture patterns; (2) analyze distal fibula fracture rates in NFL athletes by position, type of play, and contact type; (3) determine the rates of distal fibula fracture surgery in NFL athletes; and (4) report the days missed due to distal fibula fractures in NFL athletes.

Study Design:

Descriptive epidemiology study.

Methods:

A retrospective review of distal fibula fractures reported to the NFL from 2000 to 2014 was performed using the NFL Injury Surveillance System. All distal fibula fractures were included, along with isolated and combined fracture patterns. Stress fractures and proximal fibula fractures were excluded. Epidemiological data and rates of surgery were determined. Return to sport was calculated and stratified by injury pattern and management.

Results:

Overall, 237 distal fibula fractures in NFL athletes from 2000 to 2014 were included; 197 (83%) were isolated distal fibula fractures. A mean of 16 distal fibula fractures occurred each year (median, 16 per year). Fractures occurred most frequently on running (38%) and passing (24%) plays, but the frequency was next highest on kickoffs (16%), despite the relative infrequency of kickoffs during the average game compared with other play types. Surgery was reported for more than half of all distal fibula fractures (n = 128, 54%). Overall, patients who underwent surgery missed significantly more days (mean, 123.8 days) than players who did not undergo surgery (mean, 75.3 days) (P < .001). Players with isolated distal fibula fractures had significantly fewer days missed (mean, 93.6 days) compared with those with combined patterns (mean, 132.3 days) (P = .0004).

Conclusion:

Fibula fractures affect a number of NFL athletes and result in significant time missed from competition. Further research is required to determine the optimal management of fibula fractures in NFL athletes. In this study, time to return to play depended on both the fracture pattern and whether surgery was required and ranged from 72 to 145 days.

Team Logo Predicts Concussion Risk: Lessons in Protecting a Vulnerable Sports Community from Misconceived, but Highly Publicized Epidemiologic Research

BACKGROUND

Observational research has linked altitude to concussion risk, but the physiologic and epidemiologic bases for this association remain questionable.

METHODS

We performed a retrospective cohort study by analyzing four seasons of National Football League data from a widely used database (Concussion Watch) to determine if previous claims that altitude ≥196 m reduced concussion risk were replicable and whether an arbitrary predictor variable (animal vs. non-animal team logo) was related to concussion risk. Relative risk (RR) and 95% confidence intervals (95% CIs) were computed.

RESULTS

The previous association with altitude was reproduced for earlier seasons, but not replicable for recent seasons (RR = 0.92 [95% CI = 0.70, 1.22]). Across four combined seasons, "higher altitude" (RR = 0.78 [0.64, 0.96]) and animal logo (RR = 0.75 [0.63, 0.89]) were similarly associated with reduced concussion risk.

CONCLUSIONS

Inconsistent epidemiologic effects, combined with weak physiologic rationale, suggest links between altitude and concussion are coincidental. Interdisciplinary critique of concussion research is necessary to ensure that marketing claims and clinical recommendations are scientifically justified.See video abstract at, http://links.lww.com/EDE/B234.