Context

The National Collegiate Athletic Association held the first women's soccer championship in 1982; sponsorship and participation have greatly increased since.

Background

Routine examinations of athlete injuries are important for identifying emerging temporal patterns.

Methods

Exposure and injury data collected in the National Collegiate Athletic Association Injury Surveillance Program during the 2014–2015 through 2018–2019 seasons were analyzed. Injury counts, rates, and proportions were used to describe injury characteristics, and injury rate ratios were used to examine differential injury rates.

Results

The overall injury rate was 8.33 per 1000 athlete-exposures. Lateral ligament complex tears (ankle sprains) (8.6%), concussions (8.3%), and quadriceps tears (5.0%) were the most commonly reported injuries. Rates of lateral ligament complex tears followed an increasing trajectory during the study period, whereas quadriceps tear rates fluctuated during the early years, and concussion rates decreased then increased.

Summary

The findings of this study were mostly consistent with existing evidence; notable temporal patterns were observed with regard to lateral ligament complex tears and concussions.

Key Points
  • Across the study period, the competition injury rate was consistently higher than the practice injury rate; competition injury rates also followed an increasing trajectory between 2014–2015 and 2018–2019.

  • The overall preseason injury rate was higher than the regular season and postseason injury rates; however, postseason injury rates increased during 2016–2017 to 2018–2019 while preseason and regular season injury rates remained relatively stable during these years.

  • Most injuries were classified as sprains, strains, or contusions; ankle sprains, concussions, and quadriceps tears were the most commonly reported specific diagnoses.

Soccer, known as one of the most popular sports internationally,1,2  continues to grow in participation and circulates among communities of all demographics in the United States. Particularly during the years of 2014–2015 to 2018–2019, women's soccer has gathered further national attention, with a women's professional league gaining traction and the US women's national team winning a world cup in 2015.3,4  Unsurprisingly, women's soccer has also continued to gain momentum at the collegiate level in recent years. In the 1981–1982 season, the National Collegiate Athletic Association (NCAA) reported only 80 women's soccer teams across all 3 divisions; that number has since dramatically increased to 1041 in the 2018–2019 season.5  Further, the total number of women's soccer players increased from 26 995 in the 2014–2015 season to 28 310 in 2018–2019 season.5  Given the high injury rates observed in women's soccer (relative to other NCAA women's sports),6  the dynamics of the game, and the physical demands involved, it follows that studying injuries specific to women's soccer warrants due attention, as it can reveal relationships between injury incidence and their subsequent outcomes.

Surveillance systems are commonly used by researchers to observe evolving trends among large populations. Sports injury surveillances systems are essential for spawning new ideas related to injury patterns among athlete and sports injury-specific subgroups. The NCAA established an injury surveillance system in 1982,7  which is now the NCAA Injury Surveillance Program (ISP), to capture exposures, mechanisms, and details related to the injury.8  This compendium of deidentified data has been widely requested by researchers. Prior researchers using data collected by ISP to describe injuries in women's soccer have revealed notable findings.912  Across all divisions, Dick et al12  (using data captured by the NCAA ISP between 1988 and 2003) and DiStefano et al11  (using data captured by the NCAA ISP between 2004 and 2014) observed greater injury rates during competition than during practice.11,12  Roos et al9  observed comparable estimates using data captured by NCAA ISP from 2009–2010 to 2014–2015. In these studies, researchers have also shown that although ankle, knee, and upper leg injuries remained the most common injuries among NCAA women's soccer players particularly in practices, head or face injuries were also commonly reported competition injuries in this group.9,11,12  Notably, however, no researchers have examined the epidemiology of NCAA women's soccer injuries since 2015.

Updated epidemiological studies aid injury prevention efforts by describing emerging patterns in injury incidence, identifying the factors related to injury incidence, and informing strategies with the potential to reduce injury risk and severity.13,14  It is particularly important to report trends in NCAA women's soccer-related injuries to better position athletic trainers and sports medical staff at member institutions to care for their student-athletes. Thus, the purpose of this study was to describe the epidemiology of women's soccer-related injuries captured by the NCAA ISP during the 2014–2015 to 2018–2019 athletic seasons.

METHODS

Study Data

Women's soccer-related exposure and injury data collected in the NCAA ISP during 2014–2015 to 2018–2019 were used in this analysis. NCAA ISP methods were reviewed and approved as an exempt study by the NCAA Research Review Board, and the methods of the surveillance program are detailed separately within this special issue.15  In summary, athletic trainers at participating institutions contributed relevant injury and exposure data by using their clinical electronic medical record systems. A reportable injury was one that occurred due to participation in an organized intercollegiate practice or competition and required medical attention by a team certified athletic trainer or physician (regardless of time loss [TL]). Scheduled team practices and competitions during the competitive season were considered reportable exposures for this study. Data from 29 (3% of membership) participating programs in 2014–2015, 24 (2% of membership) in 2015–2016, 36 (4% of membership) in 2016–2017, 46 (4% of membership) in 2017–2018, and 109 (11% of membership) in 2018–2019 qualified for inclusion in these analyses. Qualification criteria are detailed in the aforementioned methods manuscript.15 

Statistical Analysis

Injury counts and rates (per 1000 AEs, for which 1 AE was defined as 1 athlete participating in 1 exposure event) were examined across event type (practice or competition), competition level (Division I, Division II, or Division III), season segment (preseason, regular season, or postseason), and TL (TL or non-TL [NTL]). Poststratification sample weights by sport and division are established within the ISP to compute national estimates of injury events based on the sampled teams; weighted and unweighted rates were estimated for this study, and results are presented in terms of unweighted rates (unless otherwise specified) due to low frequencies of injury observations across levels of certain explanatory variables. Temporal patterns in injury rates across the study period were evaluated using stratified (by levels of the aforementioned variables) rate profile plots. Similarly, temporal trends in rates of most commonly reported injuries were also examined across the study period. Injury counts and proportions were examined by TL (TL or NTL), body parts injured, mechanism of injury (player contact, surface contact, ball contact, other contact, noncontact, or overuse) injury diagnoses, playing positions (goalkeeper, defender, midfielder, forward, or striker), and activities. Injury rate ratios (IRRs) were used to examine differential injury rates across event types, competition levels, and season segments. IRRs with associated 95% confidence intervals (CIs) excluding 1.00 were considered statistically significant, and all analyses were conducted using SAS 9.4 (SAS Institute).

RESULTS

A total of 3932 women's soccer injuries from 454 330 AEs were reported to the NCAA ISP during the 2014–2015 to 2018–2019 athletic seasons (rate = 8.65 per 1000 AEs). This equated to a national estimate of 89 917 injuries overall (Table 1). The competition injury rate across the study period was higher than the practice injury rate (IRR = 2.81; 95% CI = 2.64, 2.99). Competition injury rates steadily increased across the study period, whereas practice injury rates remained relatively stable (Figure A). The overall Division II injury rate across the study period (rate = 9.55 per 1000 AEs) was higher than the Division I (rate = 7.48 per 1000 AEs), and Division III (rate = 9.26 per 1000 AEs) injury rates. Statistically significant differences were observed between the Division I and Division II rates (IRR = 0.78; 95% CI = 0.73, 0.84), as well as between the Division I and Division III rates (IRR = 0.81; 95% CI = 0.75, 0.87).

Table 1

Reported and National Estimates of Injuries, AEs, and Rates per 1000 AEs by Event Type Across Divisionsa

Reported and National Estimates of Injuries, AEs, and Rates per 1000 AEs by Event Type Across Divisionsa
Reported and National Estimates of Injuries, AEs, and Rates per 1000 AEs by Event Type Across Divisionsa
Figure

Temporal patterns in injury rates between 2014–2015 and 2018–2019. A, Overall injury rates (per 1000 AEs) stratified by event type (practices or competitions). B, Injury rates (per 1000 AEs) stratified by season segment. C, Rates (per 1000 AEs) of time loss injuries stratified by event type (practices or competitions). D, Rates (per 10 000 AEs) of most commonly reported injuries. All rates are unweighted and based on reported data.

Figure

Temporal patterns in injury rates between 2014–2015 and 2018–2019. A, Overall injury rates (per 1000 AEs) stratified by event type (practices or competitions). B, Injury rates (per 1000 AEs) stratified by season segment. C, Rates (per 1000 AEs) of time loss injuries stratified by event type (practices or competitions). D, Rates (per 10 000 AEs) of most commonly reported injuries. All rates are unweighted and based on reported data.

Injuries by Season Segment

During the 2014–2015 to 2018–2019 athletic seasons, 1114 preseason injuries (national estimate: 27 476), 2691 regular season injuries (national estimate: 60 097), and 127 postseason injuries (national estimate: 2344) were reported (Table 2). The preseason injury rate was higher than regular season (IRR = 1.16; 95% CI = 1.08, 1.24) and postseason (IRR = 1.58; 95% CI = 1.32, 1.90) injury rates. Preseason injury rates increased between 2014–2015 and 2015–2016, decreased between 2015–2016 and 2016–2017, and remained steady thereafter (Figure B). Conversely, regular season injury rates steadily increased across the study period, and postseason injury rates notably increased between 2016–2017 and 2018–2019 (Figure B).

Table 2

Reported and National Estimates of Injuries, AEs, and Rates per 1000 AEs by Season Segment Across Divisionsa

Reported and National Estimates of Injuries, AEs, and Rates per 1000 AEs by Season Segment Across Divisionsa
Reported and National Estimates of Injuries, AEs, and Rates per 1000 AEs by Season Segment Across Divisionsa

Time Loss

Under one-half (39.0%) of all reported injuries resulted in TL of >1 day (TL was not reported in ∼21% of all reported injuries). A comparable proportion of competition (39.4%) and practice (38.7%) injuries were TL injuries. Rates of competition-related TL rates generally increased across the study period (Figure C). Conversely, rates of practice-related TL injuries remained relatively steady across the study period (Figure C).

Injury Characteristics

Knee injuries (16.7%), ankle injuries (14.8%), and thigh injuries (14.7%) accounted for the largest proportions of all women's soccer injuries reported between 2014–2015 and 2018–2019 (Table 3). Head or face injuries were also common, particularly in competitions (17.0%). Notably, head or face injuries and ankle injuries accounted for larger proportions of competition injuries than practice injuries (Table 3). Conversely, hip or groin injuries and thigh injuries accounted for larger proportions of practice injuries than competition injuries (Table 3). Approximately one-third of all reported injuries were attributable to player contact mechanisms (29.2%); a larger proportion of all competition injuries (44.8%) than practice injuries (14.9%) were attributable to player contact mechanisms. Although notable proportions of all injuries were also attributable to noncontact (23.3%) and overuse (17.6%) mechanisms, both mechanisms accounted for larger proportions of practice-related injuries than competition-related injuries (Table 3).

Table 3

Distribution of Injuries by Body Part, Mechanism, and Injury Diagnosisa

Distribution of Injuries by Body Part, Mechanism, and Injury Diagnosisa
Distribution of Injuries by Body Part, Mechanism, and Injury Diagnosisa

Overall, most women's soccer injuries reported during the 2014–2015 to 2018–2019 seasons were strains (21.7%), sprains (21.6%), and contusions (12.5%). Inflammatory conditions (most reported in lower leg or Achilles, knee, or foot or toes; and at a markedly higher rate in preseason [rate = 1.43 per 1000 AEs] than in regular season [rate = 0.65 per 1000 AEs] and postseason [rate = 0.73 per 1000 AEs]) were also common overall (9.9%) and accounted for a notable proportion of practice injuries (14.1%). Sprains (most reported in lower knee and ankle) accounted for a larger proportion of competition injuries (26.5%) than practice injuries (17.0%). Similarly, a larger proportion of competition injuries (17.8%) than practice injuries (7.7%) were contusions. Conversely, strains accounted for a larger proportion of practice injuries (26.8%) than competition injuries (16.1%). The most commonly reported specific injuries during the study period were partial or complete lateral ligament complex tears (ankle sprains; 8.6%), concussions (8.3%), and partial or complete quadriceps tears (5.0%). Notably, partial or complete ACL tears accounted for 3.0% of all reported injuries during the study period. Rates of lateral ligament complex tears steadily increased throughout the study period (Figure D). Rates of concussion decreased between 2014–2015 and 2015–2016 and increased thereafter (Figure D), whereas rates of quadriceps tears fluctuated between 2014–2015 and 2016–2017 and remained stable thereafter (Figure D).

Injuries by Soccer-Specific Activities and Playing Positions

Most injuries in women's soccer during the 2014–2015 to 2018–2019 seasons occurred during general play (33.1%). Running (11.1%) and defending (10.5%) together accounted for over one-fifth of all reported injuries (Table 4). Comparable proportions of competition (32.3%) and practice (33.8%) injuries occurred during general play. Conversely, a larger proportion of practice injuries (13.8%) than competition injuries (8.2%) occurred during running, and a larger proportion of competition injuries (13.6%) than practice injuries (7.6%) was attributable to defending. With regard to playing position, injuries to midfielders accounted for the largest proportion of reported injuries during the study period (Table 4).

Table 4

Distribution of Injuries by Injury Activity and Playing Positiona

Distribution of Injuries by Injury Activity and Playing Positiona
Distribution of Injuries by Injury Activity and Playing Positiona

SUMMARY

In this study, we aimed to describe the epidemiology of soccer-related injuries among NCAA women's soccer players during the 2014–2015 through 2018–2019 athletic seasons. The competition injury rate was higher than the practice injury rate across the study period. Although this finding consistent with the existing literature in this population,11,12  the competition injury rate notably followed an increasing pattern throughout the study period. In comparison, the practice injury rate remained relatively stable, and therefore, the trajectory of competition injury rates after 2018–2019 warrants targeted monitoring. With regard to season segment, although preseason injury rates were higher than regular and postseason injury rates across the study period overall, postseason injury rates offered a notable juxtaposition to preseason and regular season injury rates during 2016–2017 to 2018–2019. Previous studies have shown higher injury rates in preseason in comparison with regular and postseason, in this group.11,12  The sharp increase in postseason injury rates indicate that postseason injuries may merit targeted attention in the years after 2018–2019 and present an avenue for detailed examinations in the future. In doing so, it is important to acknowledge the nuances of the collegiate soccer competitive season and carefully consider the composition of exposure events at various phases of the season. Future researchers conducting targeted, small-sample studies to examine postseason injuries more closely may consider factors such as fixture density (volume of games over a given time period) and acute cumulative workload to better reconcile postseason injury risk within this population.

Sprains, strains, and contusions were the most commonly reported injury diagnoses in NCAA women's soccer during 2014–2015 to 2018–2019. Notably, inflammatory conditions were also common and accounted for a higher proportion of practice injuries than contusions. While previous studies have also noted that most injuries in this population are sprains, strains, or contusions, there has been relatively less discussion surrounding inflammatory conditions in NCAA women's soccer players.11,12  Although the rate of inflammatory conditions was higher in preseason than it was in regular season and postseason, it is difficult to draw nuanced inferences about the nature of the inflammatory conditions reported within the ISP given the nature of sports injury surveillance data. In future targeted studies of soccer-related injuries among elite and collegiate women's soccer players, researchers may seek to capture more granular athlete and injury information to better characterize the risk of and recovery after inflammatory conditions within this population.

The most common specific injuries reported during the study period were partial or complete lateral ligament complex tears (ankle sprains), concussions, and partial or complete quadriceps tears. Incidence trajectories of concussions as well as lateral ligament complex tears across the study period indicate the need for further monitoring of these specific injuries in this population. In the case of lateral ligament complex tears, although injury rates remained stable during 2017–2018 to 2018–2019, incidence rates sharply increased across the entirety of the study period. Previous researchers have shown that lateral ligament complex tears are common in this group.16  Although some ankle injury prevention strategies have shown promising results,1721  athlete behavior and preferences are important considerations in the development of such strategies;22  and it may be critical to further prioritize the primary prevention of such injuries in this group considering the incidence trajectories observed here. Similarly, concussions rates also sharply increased during 2015–2016 to 2018–2019. Concussion rates in women's soccer have been previously reported to be among the highest within all NCAA women's sports.10  Researchers have also indicated sex differences in concussion sequelae among soccer players, suggesting that outcomes following concussions are more deleterious among women's soccer players than their male counterparts.23,24  Previous researchers have posited reasons for the observed sex differences in concussion incidence,2428  although it is important to continue examining the interplay between clinical presentations and the physiological and biomechanical underpinnings of concussions to better understand concussion risk and its associated effect on the quality of life among women's soccer players. Importantly, although these incidence trajectories offer a valuable insight into the incidence of commonly observed injuries among NCAA women's soccer players, it is reasonable to exercise caution while drawing inferences based on the observed trajectories. In particular, it is important to juxtapose these patterns to ISP participation noted previously in this article. ISP participation among NCAA women's soccer programs continuously improved throughout the study period; although it markedly improved between 2016–2017 and 2018–2019. With that said, it is reasonable to suggest that the latter years of this study period offer a more stable estimation, as well as a better representation of injury incidence in this population (compared with the earlier years). It follows that, under the tacit assumption of continued improvements in ISP participation, the incidence trajectories of these specific injuries warrant close monitoring after 2018–2019 to better understand the burden posed by them to this population.

Routine monitoring of NCAA women's soccer injuries is important and will provide valuable insight into injury incidence and outcomes within this population. Here, we show that although injury incidence was temporally stable within this population in some regard, routine surveillance has the capacity to highlight emerging patterns. Ultimately, these emerging patterns offer the platform upon which to build targeted studies in which researchers reconcile the etiology underpinning injury risk and sequelae in this group.

ACKNOWLEDGMENTS

The NCAA Injury Surveillance Program was funded by the NCAA. The Datalys Center is an independent nonprofit organization that manages the operations of the NCAA ISP. The content of this report is solely the responsibility of the authors and does not necessarily represent the official views of the funding organization. We thank the many ATs who have volunteered their time and efforts to submit data to the NCAA- ISP. Their efforts are greatly appreciated and have had a tremendously positive effect on the safety of collegiate student-athletes.

REFERENCES

2. 
Allmers
S,
Maennig
W.
Economic impacts of the FIFA soccer world cups in France 1998, Germany 2006, and outlook for South Africa 2010
.
East Econ J
.
2009
;
35
(4)
:
500
519
.
3. 
Miller
G,
Scheyer
J,
Sherrard
E.
Women's soccer in the U.S.
Soccer Politics
.
Updated
2013
.
Accessed March 5, 2021.
4. 
A tournament that broke all records
.
FIFA
.
Accessed March 5,
2021
.
5. 
Sports sponsorship and participation rates database—student-athletes
.
NCAA
.
Accessed March 5,
2021
.
6. 
Kerr
Z,
Marshall
S,
Dompier
T,
Corlette
J,
Klossner
D,
Gilchrist
J.
College sports–related injuries—United States, 2009–10 through 2013–14 academic years
.
MMWR Morb Mortal Wkly Rep
.
2015
;
64
(48)
:
1330
1336
.
7. 
Dick
R,
Agel
J,
Marshall
SW.
National Collegiate Athletic Association Injury Surveillance System commentaries: introduction and methods
.
J Athl Train
.
2007
;
42
(2)
:
173
182
.
8. 
Kerr
ZY,
Comstock
RD,
Dompier
TP,
Marshall
SW.
The first decade of web-based sports injury surveillance (2004–2005 through 2013–2014): methods of the National Collegiate Athletic Association Injury Surveillance Program and High School Reporting Information Online
.
J Athl Train
.
2018
;
53
(8)
:
729
737
.
9. 
Roos
KG,
Wasserman
EB,
Dalton
SL,
et al
Epidemiology of 3825 injuries sustained in six seasons of National Collegiate Athletic Association men's and women's soccer (2009/2010–2014/2015)
.
Br J Sports Med
.
2017
;
51
(13)
:
1029
1034
.
10. 
Zuckerman
SL,
Kerr
ZY,
Yengo-Kahn
A,
Wasserman
E,
Covassin
T,
Solomon
GS.
Epidemiology of sports-related concussion in NCAA athletes from 2009–2010 to 2013–2014: incidence, recurrence, and mechanisms
.
Am J Sports Med
.
2015
;
43
(11)
:
2654
2662
.
11. 
DiStefano
LJ,
Dann
CL,
Chang
CJ,
et al
The first decade of web-based sports injury surveillance: descriptive epidemiology of injuries in US high school girls' soccer (2005–2006 Through 2013–2014) and National Collegiate Athletic Association women's soccer (2004–2005 Through 2013–2014)
.
J Athl Train
.
2018
;
53
(9)
:
880
892
.
12. 
Dick
R,
Putukian
M,
Agel
J,
Evans
T,
Marshall
SW.
Descriptive epidemiology of collegiate women's soccer injuries: National Collegiate Athletic Association Injury Surveillance System, 1988–1989 through 2002–2003
.
J Athl Train
.
2007
;
42
(2)
:
278
285
.
13. 
van Mechelen
W,
Hlobil
H,
Kemper
HCG.
Incidence, severity, aetiology and prevention of sports injuries. A review of concepts
.
Sports Med
.
1992
;
14
(2)
:
82
99
.
14. 
Chandran
A,
Nedimyer
AK,
Register-Mihalik
JK,
DiPietro
L,
Kerr
ZY.
Comment on: “Incidence, severity, aetiology and prevention of sports injuries: a review of concepts.”
Sports Med
.
2019
;
49
(10)
:
1621
1623
.
15. 
Chandran
A,
Morris
SN,
Wasserman
EB,
Boltz
A,
Collins
CL.
Methods of the National Collegiate Athletic Association Injury Surveillance Program, 2014–2015 Through 2018–2019
.
J Athl Train
.
2021
;
56
(7)
:
616–621.
16. 
Roos
KG,
Kerr
ZY,
Mauntel
TC,
Djoko
A,
Dompier
TP,
Wikstrom
EA.
The epidemiology of lateral ligament complex ankle sprains in National Collegiate Athletic Association sports
.
Am J Sports Med
.
2017
;
45
(1)
:
201
209
.
17. 
Verhagen
E,
van Der Beek
A,
Twisk
J,
Bouter
L,
Bahr
R,
van Mechelen
W.
The effect of a proprioceptive balance board training program for the prevention of ankle sprains: a prospective controlled trial
.
Am J Sports Med
.
2004
;
32
(6)
:
1385
1393
.
18. 
McGuine
TA,
Keene
JS.
The effect of a balance training program on the risk of ankle sprains in high school athletes
.
Am J Sports Med
.
2006
;
34
(7)
:
1103
1111
.
19. 
Bahr
R,
Lian
O,
Bahr
IA.
A twofold reduction in the incidence of acute ankle sprains in volleyball after the introduction of an injury prevention program: a prospective cohort study
.
Scand J Med Sci Sports
.
1997
;
7
(3)
:
172
177
.
20. 
Eils
E,
Schröter
R,
Schröder
M,
Gerss
J,
Rosenbaum
D.
Multistation proprioceptive exercise program prevents ankle injuries in basketball
.
Med Sci Sports Exerc
.
2010
;
42
(11)
:
2098
2105
.
21. 
Kaminski
TW,
Needle
AR,
Delahunt
E.
Prevention of lateral ankle sprains
.
J Athl Train
.
2019
;
54
(6)
:
650
661
.
22. 
Janssen
K,
van Den Berg
A,
van Mechelen
W,
Verhagen
E.
User survey of 3 ankle braces in soccer, volleyball, and running: which brace fits best?
J Athl Train
.
2017
;
52
(8)
:
730
737
.
23. 
Chandran
A,
Barron
MJ,
Westerman
BJ,
DiPietro
L.
Multifactorial examination of sex-differences in head injuries and concussions among collegiate soccer players: NCAA ISS, 2004–2009
.
Inj Epidemiol
.
2017
;
4
(1)
:
28
.
24. 
Covassin
T,
Moran
R,
Elbin
RJ.
Sex differences in reported concussion injury rates and time loss from participation: An update of the national collegiate athletic association injury surveillance program from 2004–2005 through 2008–2009
.
J Athl Train
.
2016
;
51
(3)
:
189
194
.
25. 
Kroshus
E,
Baugh
CM,
Stein
CJ,
Austin
SB,
Calzo
JP.
Concussion reporting, sex, and conformity to traditional gender norms in young adults
.
J Adolesc
.
2017
;
54
:
110
119
.
26. 
Delaney
JS,
Lacroix
VJ,
Leclerc
S,
Johnston
KM.
Concussions among university football and soccer players
.
Clin J Sport Med
.
2002
;
12
(6)
:
331
338
.
27. 
Johnston
KM,
McCrory
P,
Mohtadi
NG,
Meeuwisse
W.
Evidence-based review of sport-related concussion: clinical science
.
Clin J Sport Med
.
2001
;
11
(3)
:
150
159
.
28. 
Covassin
T,
Elbin
RJ,
Harris
W,
Parker
T,
Kontos
A.
The role of age and sex in symptoms, neurocognitive performance, and postural stability in athletes after concussion
.
Am J Sports Med
.
2012
;
40
(6)
:
1303
1312
.

Author notes

Authors Avinash Chandran and Sarah N. Morris have contributed equally to manuscript preparation. The articles in this issue are published as accepted and have not been edited.