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Enhancing Public Dissemination and Understanding of Injury Risk in Sport

This week’s EXSS Impact Post is by Dr. Zack Kerr, Assistant Professor in Exercise and Sport Science.  Dr. Kerr is an epidemiologist and explores different reporting methods of injury epidemiology data to improve public dissemination and understanding.

Why did you do this study?

Over the past decade, I have immersed myself in the world of sports injury surveillance. The findings are of great importance because they are the basis for many data-driven decisions regarding the rules and safety in sports organizations such as the National Collegiate Athletic Association (NCAA) and the National Federation of State High School Associations (NFHS).

However, at times, I found it difficult to discuss findings to stakeholders of sports organizations, such as parents, coaches, and administrators, because we in academia like to rely on the injury rate to measure injury incidence. The injury rate is defined as:

injury-rate

Injury rates are preferred because they account for all injury events in the numerator, regardless of whether or not these were sustained by the same athletes. They also account for variation in the amount of exposure time via the denominator; thus, an athlete that plays more across a season provides more exposure time. But for many parents, what matters most to them is knowing the risk; in other words, what is the probability that their child will get injured within a specific timeframe (e.g. one season).

As a result, using data from the NCAA Injury Surveillance Program, I worked with a team of epidemiologists and athletic trainers to examine a variety of methods of measuring injury incidence. This team included:

  • Karen G. Roos, California State University – Long Beach
  • Aristarque Djoko, Datalys Center for Sports Injury Research and Prevention
  • Sara L. Dalton, Datalys Center for Sports Injury Research and Prevention
  • Steve P. Broglio, University of Michigan
  • Stephen W. Marshall, University of North Carolina at Chapel Hill
  • Thomas P. Dompier, Datalys Center for Sports Injury Research and Prevention

Given the interest, we opted to examine these measures with concussion.

What did you do and what did you find in this study?

We used concussion data from the NCAA Injury Surveillance Program during the 2011/12-2014/15 academic years. The NCAA Injury Surveillance Program has been in existence since the early 1980s and have been assisting the NCAA in assessing sport-related safety in their sponsored programs. Participation in the NCAA Surveillance Program varied by sport and academic year. Data were collected by team athletic trainers that worked with these sport programs during the season.

We computed four measures of concussion incidence in a 13 different sports:

Men’s sports Women’s sports
–   Baseball

–   Basketball

–   Football

–   Ice Hockey

–   Lacrosse

–   Soccer

–   Wrestling

–   Basketball

–   Field hockey

–   Ice hockey

–   Lacrosse

–   Softball

–   Volleyball

The four measures are described in the table below.

Concussion rate

At what rate are concussions sustained during at-risk exposures?

Example: Across 10,000 NCAA football athlete-exposures, we expect to see 6-7 concussions

One-season risk of concussion

What is the probability of an athlete obtaining a concussion in one season?

Example: In one season, we expect 1 in 20 NCAA football players to have a concussion?

Average # concussion per team per season

How many concussions does a team sustain in one season?

Example: In one season, we expect 5-6 concussions within a NCAA football team

% teams with a concussion

How many teams have a concussion occur within a season?

Example: In one season, we expect 80.6% of all NCAA football teams to have at least one concussion

The computations for the measures included alongside rates are included below:

risk

avg-per-season

teams

What we found is that despite some variation in the rank-order of included sports, full contact sports such as wrestling, football, and ice hockey consistently generated the highest incidence of concussion.

fig1-kerr

figure-2-kerr

figure-3-kerr

figure-4-kerr

Despite the similar rankings across sports, we believe that squad size may serve as a confounder, particularly in football. Furthermore, such measures can be biased when comparing incidence across teams (or sports) that vary greatly by the number of athletic sessions per season. Thus, it is important for readers to understand the strengths and limitations of measures of injury incidence utilized by various researchers.

How do these findings impact the public?

Although injury rates are the most preferred method of gauging injury incidence in academia, they may not be intuitive to non-scientists, including members of sports organizations concerned about the incidence of injury among their players. To help parents, coaches, and athletes, and to drive the development of data-driven, evidence-based policy and rule changes, we need to ensure that we are providing our findings in an easily understood manner.

This research presents a collection of “alternative facts” that still utilize the data collected by athletic trainers in a valid manner, but may be easier to interpret and disseminate to stakeholders. Better yet, these measures are applicable to other injuries and settings. This more diverse “toolbox” of measures, in combination with traditional athlete-based rates, may help sports organizations better identify specific athletes at risk for injury.

Epidemiology of Hip Flexor and Hip Adductor Strains in National Collegiate Athletic Association Athletes, 2009/10-2014/15

Research Team Members: Timothy G. Eckard, PT, DPT, OCS, Darin A. Padua, PhD, ATC, Thomas P. Dompier, PhD, ATC, Sara Dalton M.Ed, LAT, ATC, Kristian Thorborg, PT, PhD, Zachary Y. Kerr, PhD, MPH

hip-adductorsWhy did you do this study?

Lower extremity muscle strains are common in collegiate sports. Strains result in significant participation restriction time for athletes, as they often require extensive rehabilitation and frequently recur. Two muscle groups vulnerable to strain injury in sports are the hip flexor and hip adductor groups. The hip flexor muscles, including the psoas major and the iliacus (i.e., the iliopsoas group), are injured in athletic activities such as sprinting, kicking, and cutting. The adductor group shares the same mechanisms of injury and consists of muscles in the medial compartment of the thigh including the pectineus, adductor magnus, adductor longus, adductor brevis, obturator externus, and gracilis. Elucidating the rates and patterns of these injuries in collegiate athletes will help determine the need for primary and secondary prevention programs in various NCAA sports. However, research on hip flexor and hip adductor strains has been mostly limited to professional athletes and frequently does not distinguish between strains of the disparate muscle groups around the hip. Therefore, the purpose of our study was to describe the epidemiology of hip flexor and hip adductor strains in 25 NCAA sports.

hip-flexorsWhat did you do and what did you find in this study?

Rates and patterns of hip flexor and hip adductor strains in collegiate sports were examined in a sample of NCAA varsity teams from 25 sports. Rates and distributions of strains by mechanism, recurrence, and time loss were examined. Rates were then compared within and between sports by event type (practice versus competition), sex, mechanism, recurrence, and time loss. A total of 770 hip flexor and 621 hip adductor strains occurred over the six academic years examined. The highest rates were in men’s soccer and men’s ice hockey. Most strains occurred in practice, but the rate of both types of strains was higher in competition. In sex-comparable sports, the hip flexor strain rate did not differ between the sexes but the hip adductor strain rate was higher in men than women. Non-contact was the most common mechanism for both types of strains, and most resulted in less than one week of time loss.

soccer-playerHow do these findings impact the public?

Our findings suggest that prevention programs for hip flexor strains should be developed and implemented across male and female sports teams, particularly in soccer and ice hockey. Male sports teams, especially soccer and ice hockey teams, should place an emphasis on prevention programs for hip adductor strains. Secondary prevention programs involving thorough rehabilitation and strict return to play criteria should be developed and implemented to curb the high recurrence rate of these injuries, particularly in ice hockey.

 

Sponsorship Revenue Forecasting for Sport Organizations: A Survival Analysis Approach

Research Team Members: Jonathan A. Jensen*, Brian A. Turner†, Natalie Caneja*, David Head*, Akash Mishra*, and Tyler Wisniewski*

* University of North Carolina, Chapel Hill, NC; † The Ohio State University, Columbus, OH

Why did you do this study?

university-athletic-departments-are-increasngly-reliant-on-apparel-sponsorships-and-multimedia-rights-agreementsOne of the more important evolutions in the sport industry over the past decade has been the marked increase in the application of advanced methodologies to ascertain patterns in data, or analytics. Numerous new methodological approaches are now being applied to assist sport organizations in decision-making relative to scouting, player development, and resource allocation. However, analytics are just now beginning to be applied off of the field to the business side of sport organizations, in areas such as ticket pricing and sales.

One area that has yet to be impacted by this trend in the application of analytics is revenue projections and forecasting. Despite monumental gains in other areas, revenue forecasts for many sport organizations still largely depend on the renewal rate, simply the annual percentage of sponsors or ticket holders who renew their relationship with the organization.

This research offers a new approach to the analysis and forecasting of revenue from an increasingly important revenue source for sport organizations, commercial sponsorship. Many non-profit sport organizations, such as the International Olympic Committee (IOC), the United States Olympic Committee (USOC) and their many National Governing Bodies (NGBs), as well as the National Collegiate Athletic Association (NCAA) and intercollegiate athletic departments at its member institutions, depend on commercial sponsorship for an increasingly larger portion of their annual revenue.

What did you do and what did you find in this study?

the-non-profit-international-olympic-committee-ioc-relies-on-sponsorship-for-44-of-its-annual-revenueGiven these challenges, the purpose of this research is to apply advanced methodological approaches to assist these various types of organizations

in sponsorship revenue forecasting. Specifically, this research represents the first application of survival analysis modeling approaches in an empirical investigation of the duration of sponsorships. Typically utilized in the biostatistics and medical fields, survival analysis approaches can provide a wealth of additional information about the duration of sponsorships. For example, rather than simply providing information on how many sponsors typically renew, this approach unearths a variety of additional information, including when the probability of a sponsor ending its relationship is the highest and the median lifetime of the sponsorships.

Initial results of the research, which was named a finalist in the research paper competition at the 2016 MIT Sloan Sports Analytics Conference and is slated to be published in Sport Marketing Quarterly, has utilized the context of global sport organizations, such as the International Olympic Committee (IOC) and the Fédération Internationale de Football Association (FIFA). Current research being performed in conjunction with students in the UNC Sport Administration program extends the research to the context of intercollegiate athletics, including athletic apparel sponsorships, multimedia rights agreements, title sponsorships of postseason bowl games, and naming rights agreements of facilities. Future research involves the insertion of covariates into the models, to ascertain whether there are certain conditions or factors that can actually predict the end of these partnerships.

How do these findings impact the public?

from-2011-14-the-fifa-world-cup-generated-more-than-1-6-billion-in-revenue-from-sponsorshipThe impact of the research involves assisting non-profit sport organizations in particular in improving their understanding of when these marketing partnerships are most susceptible to dissolution and their ultimate duration, as well as what factors may be predictive of the end of such partnerships. Given that many non-profit sport organizations depend on sponsorship revenue for their survival, these efforts help them to better forecast revenue they receive from this increasingly important source. In addition, the identification of covariates that may be statistically significant predictors of the dissolution of such partnerships may help these organizations isolate certain factors that should be closely monitored throughout the relationship, and identify the types of sponsors more likely to enter into longer-term relationships that can help guarantee the survival of the organization for many years to come.

Testing Strength in ACL Reconstructed Patients: Is Symmetry the Answer?

This is a summary of a recently published article in Medicine and Science of Sport and Exercise entitled “Quadriceps Strength Predicts Self-Reported Function Post ACL Reconstruction”.

Dr. Pietrosimone’s co-authors on this paper include Adam Lepley, Matthew Harkey, Brittney Luc- Harkey, Troy Blackburn, Phillip Gribble, Jeffrey Spang and David Sohn.

Why Did We Perform this Study

quadriceps-musclesQuadriceps muscle weakness is common following anterior cruciate ligament (ACL) injury and ACL reconstruction. This muscle weakness often persists many years after someone has undergone knee surgery and returned to participation in physical activity. Quadriceps weakness often leads to greater disability in those with ACL reconstruction, and there is evidence that quadriceps dysfunction may negatively impact gait mechanics that can increase the risk of developing knee osteoarthritis. Therefore, it is critical for patients who have undergone ACL reconstruction to maximize quadriceps strength following surgery and maintain optimal quadriceps strength throughout their lifetime. Unfortunately, it remains unclear how much quadriceps strength is needed to function at a high level following ACL reconstruction. Furthermore, there are no established best practice guidelines for quantifying quadriceps strength in patients with an ACL reconstructions. Traditionally, many clinicians and researchers have compared quadriceps strength of the injured limb to that of the uninjured limb; thereby trying to maximize the strength symmetry between limbs after ACL injury. Conversely, we have previously reported that greater overall quadriceps strength, normalized to the body mass of the individual, is strongly associated with self-reported disability in those with an ACL reconstruction. Therefore, in this study, we wanted to determine the best method for using quadriceps strength to predict self-reported function following ACL reconstruction. We felt that this study would help us develop valuable clinical cuff-off scores that could be used to guide strengthening regimens for patients with an ACL reconstruction.

What we did in this study

strength-test

We tested isometric quadriceps strength at 90-deg of knee flexion. Most individuals following ACL injury and reconstruction can be tested in this position at multiple time points. Also, testing in this manner may be more easily conducted with a range of strength testing instrumentation in clinical and research settings.

We recruited 96 individuals with a primary ACL reconstruction on only one limb (62 females and 34 males; 21.7±3.85 years old; 37.04 ± 36.7 [range 6-161] months post ACLR). We tested the maximal strength quadriceps strength on each limb in a random order using a dynamometer. Each participant performed maximal voluntary isometric contractions in a seated position with their knees flexed to 90° (See Figure 1). On the same day participants completed the subjective section of the International Knee Documentation Committee Index questionnaire in order to determine the magnitude of self-reported disability for each participant. We considered anyone scoring over 90% on the International Knee Documentation Committee Index to be at a high level of function (we termed these individuals “High Functioners”). Next we created Receiver Operating Characteristic Curves to determine how well quadriceps strength predicted who would be a High Functioner. After determining the quadriceps strength cut-off scores that maximized the sensitivity and specificity for predicting the High Functioner status, we calculated odds ratios to determine how well our cut-off scores were at determining a High Functioner status.

What we found and how it Impacts Healthcare

Overall, regardless of quantification method, quadriceps strength was able to significantly predict which individuals would be High Functioners. Interestingly we found that overall quadriceps strength, normalized to body mass ,demonstrated a higher accuracy for predicting who would be a High Functioner, compared to quadriceps strength symmetry. Specifically, those who were able to produce overall quadriceps strength that exceeded 3.10 Newton-meters per kilogram of body mass demonstrated 8.15 times higher odds of being a High Functioner. Therefore, a 150lb individual (68.18 kg) would need to generate 211.36 Newton-meters of torque with their quadriceps in order meet the prescribed cut-off score. We found that individuals who achieved a strength symmetry value of 96.5% (injured limb strength/ uninjured limb strength) would have a 2.78 times higher odds of being a High Functioner. Therefore, an individual who can produce 250 Newton-meters of torque with the uninjured limb would need to produce 241.25 Newton-meters of torque on the ACL reconstructed limb to achieve this cut-off value.

Overall Strength vs Strength Symmetry

Strength symmetry has traditionally been used to determine which participants are able to generate enough strength to return to participation in physical activity. While improving strength symmetry is still important for ACL reconstructed patients, achieving symmetry alone may not be sufficient for optimizing therapeutic outcomes. It is possible that some people may demonstrate symmetrical quadriceps strength, yet they may not exhibit enough strength relative to the size of their body. Our data suggests that maximizing overall quadriceps strength to support the size of the person is critical in determining the functional status for that individual. Bilateral quadriceps weakness may be of particular concern in individuals who have a history of bilateral ACL injury. Rehabilitation goals for ACL reconstructed individuals may need to be amended to include the development of strength relative to a patient’s size rather than the contralateral limb. Bilateral strengthening may be critical for many patients in order to achieve the desired ratio on the ACL reconstructed limb (3.10 Newton-meters/ kilograms of body mass), while still marinating strength symmetry between limbs. It may also be necessary to address the maintenance of a healthy body weight, or when prudent, to lose excess non-lean body weight which will also improve the ratio of quadriceps strength to body mass. Future ACL rehabilitation guidelines should consider testing patients’ overall strength relative to their body mass in addition to strength symmetry outcomes.

Social Jetlag (Poor Sleep) Is Associated with Adiposity in Pre-Adolecsent New Zealand Children

Research Team

Lee Stroner, Nicholas Castro, Leigh Signal, Paula Skidmore, James Faulkner, Michelle Williams, Sally Lark

Why did you do this study?

poor-sleepPoor sleep behaviour, along with physical inactivity and poor diet, has been associated with childhood obesity. Several aspects of sleep may be important, including sleep duration, sleep disorders and, more recently, something called “social jet lag”. A recent meta-analysis, which included 35,540 children, reported that in children short sleep (i.e., below the recommend number of hours recommend by the National Sleep Foundation) was associated with a 71% (odds ratio [OR]: 1.71, 95%CI: 1.36-2.14) greater likelihood of obesity. Similarly, several studies have reported an association between sleep disorders and obesity in children. However, while social jetlag has been associated with being overweight (OR: 3.30, 95%CI: 2.51-4.33) in a group of over 65,000 European adults, no known studies have examined whether obesity is associated with social jetlag in children, nor has any study in Children simultaneously examined the importance of sleep duration, sleep disorders and social jetlag.

Sleep–wake and metabolism cycles, which are tightly interconnected at the molecular level, are regulated by the circadian clock. In modern society, the rhythmicity of the circadian clock is often disrupted by social obligations, including work and school schedules. Social jetlag is the discrepancy between an individual’s circadian clock and social rhythms, and is measured as the difference in hours between the midpoint of sleep at work/school and free days. Social jetlag is simple to measure, and a potentially simple health behaviour for which public health policy can be developed. Therefore, the purpose of this study was investigate whether sleep duration, sleep disorders and social jetlag are associated with body composition in pre-adolescent children

What did you do and what did you find in this study?

This cross-sectional study recruited 341 children (50% Female) aged 8–10 years from three representative sample sites across New Zealand. Body composition was estimated four ways: body fat (%), fat mass index (FMI, kg/m2), waist to hip ratio (WHR), and body mass index (BMI, kg/m2). The three sleep variables of interest were: average sleep duration, sleep disorders, and social jetlag. Sleep duration was recorded using a parent-reported, single item habitual school/weekday sleep survey. Sleep disorders were estimated using the Children’s Sleep Habits Questionnaire. Social jetlag was calculated as the absolute difference between the midpoints of sleep on weekdays versus weekend days.

Following adjustment for possible confounders, sleep duration was only associated WHR (β = -0.008, 95%CI: -0.015, 0.000), and sleep disorders was only associated with FMI (β = -0.034, 95%CI: 0.002, 0.067 kg/m2), while social jetlag was associated with all four body composition variables. A one hour increase in social jetlag was associated with a 2.98 % (95%CI: 0.41, 5.55 %) increase in body fat, 0.51 kg/m2 (95%CI: 0.11, 0.91 kg/m2) increase in FMI, a 0.90 kg/m2 95%CI: 0.21, 1.58 kg/m2) increase in BMI, and a 0.13 (95%CI: 0.003, 0.023 increase in WHR.

How do these findings impact the public?

While sleep duration, sleep disorders and social jetlag were all found to be associated with body composition in pre-adolescent children, the association between social jetlag and body composition was found to be particularly strong. This finding is important, because social jetlag is something which is relatively easy to fix, and this simple fix may result in important improvements in childhood health.

 

The goal of the Cardiometabolic Lab is continue this important work, and identify other simple lifestyle factors which improve the health of children.

 

Utility of ultrasound for body fat assessment: validity and reliability compared to a multi-compartment criterion

Research Team Members: Abbie E. Smith-Ryan,  Malia N.M. Blue, Eric T. Trexler, Katie R. Hirsh

Why did you do this study?

The importance of body composition for long term health and risk of chronic disease is expanding. It is widely recognized that high body fat is linked with a number of health disturbances, such as cardiovascular disease, metabolic abnormalities, hypertension, and sleep apnea, among others. Body composition assessment is an important aspect to be integrated within clinical practice as a preventative health approach. Specifically, patient care is shifting toward a more individualized preventative model with the establishment of patient-centered medical homes. Measurement of body composition can allow for treatment to be individualized to the patient, is predictive of disease risk, and allows for establishment of optimal nutrition and weight loss goals.

ultrasoundabbie1

Portable ultrasound unit for measurements of body composition

Due to the potential use of body composition measurement in clinical settings, accurate and portable ‘field-based’ methods are needed. Ultrasonography (US), which has been around for decades, has contrasting support for its use as an accurate measurement technique for body composition. Technological advancements have transformed US to a portable, clear-resolution imaging package that is used in a variety of clinics for standard of care practice. Due to the equipment availability and widespread use of US in clinical environments, the ability to accurately assess body composition using US would be a potentially feasible option.

Our laboratory has developed a protocol to evaluate body composition using a standard B-mode clinical ultrasound. In this particular study we evaluated the accuracy and repeatability of using a portable B-mode ultrasound in comparison to a gold standard multi-compartment criterion for per cent body fat in overweight and obese adults.

What did you do and what did you find in this study?

ultrasoundabbie2

Ultrasound image displaying fat thickness to quantify body fat percentage. Measurements taken at 7 sites.

Body fat was measured in fifty-one overweight and obese men and women to evaluate accuracy of the measurement. A subset of thirty-six individuals completed a second day of testing to obtain repeatability data. Based on the current results, US may over-predict %Fat in overweight/obese adults, but may still be a useful field-based measurement technique. The skill and time required for US measurement may be less than that required for skinfolds and other field based assessments and is more accurate than use of body mass index. Additionally, US may be more accurate than other commonly used field-based assessments. Values in the present study were more accurate for men, compared to women, which may be a function of the overall lower body fat in this sample of men. The US also proved to provide similar results from day one to day two, suggesting high repeatability.

 

How do these findings impact the public?

Ultrasound is one of few field based tools that can assess total and regional body composition. A number of new ultrasound devices are portable and compact, readily available, and widely used in clinical medicine. When comparing the overestimation of about 3.5%Fat, this is comparable to a number of other more widely accepted body composition techniques, including DEXA and BodPod, neither of which are portable. The repeatability of the US was high, providing potential use as a portable clinical tool. Using %Fat as a clinical outcome and/or tracking in the clinic, rather than body weight or BMI may be a better indicator of disease risk and progression. Future research should evaluate the feasibility of implementing such a tool within a clinic and as a component of a patient centered medical home.

Prospective Evaluation of Musculoskeletal Injury History as Predictors for Anterior Cruciate Ligament Injury Risk: The JUMP-ACL Study

Research Team Members: Darin A. Padua*, Kenneth L. Cameron, Sarah J. de la Motte, Kristen L. Kucera*, Yvonne M. Golightly*, Stephen W. Marshall*

*University of North Carolina, Chapel Hill, NC, USA; Keller Army Hospital, West Point, NY, USA; Uniformed Services University of Health Sciences, Bethesda, MD, USA

anterior_cruciate_ligament_1Why Did You Do This Study?

Anterior cruciate ligament (ACL) injuries occur in as many as 250,000 Americans each year. Within 10 years, 1 in 3 individuals who sustain an ACL injury develop signs of post-traumatic knee osteoarthritis (OA), regardless of whether or not they underwent ACL reconstruction. Radiographic evidence of knee OA rises to 52% in ACL + Meniscus injured patients at 12 years post-injury. Prior history of ACL injury increases an individual’s ACL injury risk by 4-6 times to both the previously injured and healthy opposite limb.

It is unknown if other, more common and less severe lower extremity injuries are associated with an elevated risk of ACL injury. Understanding the association between prior lower extremity injuries and incident ACL injury may help in identifying those with elevated risk for future ACL injury and post-traumatic knee OA. Individuals with a history of more common lower extremity injuries may be important to target for ACL injury and ultimately post-traumatic knee OA prevention efforts. The objective of this study was to determine if history of specific lower extremity injuries are prospective risk factors for incident ACL injury.

What Did You Do and Find In This Study?

First year cadets from the U.S. Military, U.S. Air Force or U.S. Naval Academies were enrolled in the JUMP-ACL study (Joint Undertaking to Monitor and Prevent ACL Injury) as participants as they began their 4-year officer training.  A total of  5,689 healthy, physically active first year cadets were enrolled between 2005 to 2009 (Males = 3,496; Females = 2,193; Age = 18.6 ± 0.6 yrs; Height = 173.5 ± 9.2 cm; Weight = 71.9 ± 12.9 kg). 

Participants completed a self-reported injury history questionnaire on prior injuries to the lower extremity over the past 6 months.  History of the following lower extremity injuries was obtained:

  • Ankle sprains
  • Shin splints (medial tibial stress syndrome)
  • Knee swelling / popping
  • Knee meniscus injury
  • Patellofemoral pain
  • Hip injury

Active surveillance was conducted for all participants with no prior history of ACL reconstruction at study baseline as participants were prospectively followed for 4 years. ACL injuries were ascertained through medical record abstraction at each academy and through searches of records in the Defense Medical Surveillance System, a comprehensive database of military encounters by the Armed Forces Health Surveillance Center. ACL injury was confirmed intra-operatively for 98% of injuries.

117 of the 5,689 individuals with no prior history of ACL reconstruction were later diagnosed with an incident ACL injury during the follow-up period (74 male and 43 female).  Among the primary ACL injuries, 60 (51%) were non-contact, 38 were indirect contact (32%), and 19 (16%) were direct contact.  The 4-year risk of ACL injury was 2.0% (95% CI = 1.7%, 2.4%).

The rate of ACL injury was the number of incident ACL injuries divided by total person-years at risk.  Rate ratios (RR) were calculated using multivariate Poisson regression models (adjusted for gender, testing site, and year of enrollment).

History of lower extremity injury last 6 months

RR

95% CI

p-value

No lower extremity injury history

1.00

ref

Prior hip injury

0.87

0.28, 2.75

0.81

Prior patellofemoral pain

0.95

0.55, 1.63

0.87

Prior shin splints

1.01

0.69, 1.48

0.96

Pior knee swelling / clicking

1.01

0.67, 1.51

0.97

Prior severe knee pain

1.06

0.54, 2.10

0.85

Prior knee meniscus injury

1.12

0.28, 4.56

0.87

*Prior ankle sprain

1.89

1.25, 2.86

0.002

Table 1. Adjusted rate ratios for incident ACL injury based on injury history in 6 months prior to cadet basic training (n = 5,689).

ankle-inversion-injuryHow Do These Findings Impact The Public?

Ankle sprain history was the most important predictor of ACL injury.  These findings suggest that history of an ankle sprain could be used by health care providers to target ACL injury prevention efforts. Interestingly, prior injury to the hip, knee and shin were not associated with future ACL injury risk. Ankle sprain events may be similar to ACL injury events in that an unexpected perturbation occurs where the neuromuscular system is unable to mitigate the injurious external loads.

Because ACL injury is most common in people between the ages of 15-24 years, these individuals develop knee OA very early in life adding to a myriad of inactivity related physical and psychological co-morbidities. Targeting individuals with a history of ankle sprain for ACL injury prevention efforts may prevent incident ACL injury and subsequently reduce the risk of knee OA development.

This study was funded by the NIAMS Division of NIH (R01-AR050461)