Interpreting ACL Injury Prevention Program Results: Understanding Injury Incidence Rates and Athlete-Exposures

Sue Barber-Westin

Since the first publication of a knee ligament injury prevention training program appeared in the sports medicine literature for female high school athletes in 1996 – Sportsmetrics – [1], at least 50 have followed that focused on female athletes. To date, 9 of these studies have reported ACL injury rates in female athletes according to athlete-exposures. An athlete-exposure is usually defined as one athlete participating in a practice or game in which there is the possibility of sustaining an injury. There have been a few studies on intervention programs that did not provide ACL injury rates according to athlete-exposures. Instead, these investigations provided the number of injuries divided by the number of athletes participating, which is not considered accurate according to modern epidemiology methods. One must instead use athlete-exposures to calculate injury incidence rates.

Athlete-exposures are usually determined using one of two methods. The first, which is the most accurate but difficult to collect, is the actual number of hours a player participates in practices and games throughout the season. The second method defines 1 athlete-exposure as one athlete participating in a practice or game. Therefore, if an athlete participates in 3 practices a week for 16 weeks and a total of 10 games during the season, the athlete-exposures would equal 58 for that player.

Injury incidence rates are calculated as the number of injuries divided by the total number of athlete-exposures. They may be calculated separately for practices and games, or all combined for an entire season.

To date, 3 ACL injury prevention programs have significantly reduced the rate of noncontact ACL injuries in female adolescent athletes. These include Sportsmetrics [2], Prevent Injury and Enhance Performance Program (PEP) [3], and Knee Injury Prevention Program (KIPP) [4]. The Sportsmetrics program had 700 trained athletes with 36,724 exposures and 1,120 control athletes with 61,244 exposures. There were 13 noncontact ACL injuries in the control group and just 1 in the trained group, for incidence rates of .21 and .03, respectively (p = .03). These numbers included athletes who participated in the original Sportsmetrics program and those that participated in the more recent sports-specific programs of Sportsmetrics Volleyball, Sportsmetrics Basketball, and Sportsmetrics Soccer.

It is important to note that other programs have been successful in reducing the rate of other types of lower limb injuries. For instance, the HarmoKnee program reduced the incidence of all types of acute knee injuries and all noncontact knee injuries [5]. When noncontact ACL injuries were sorted from the other knee injuries, the data did not reach statistical significance. A program from Sweden significantly reduced the incidence of ACL injuries when contact and noncontact injuries were combined [6] .

So, for medical professionals, when you hear of a claim that a program “reduced the rate of ACL injuries”, it is important to carefully study the methods used to calculate the injury rates and if contact and noncontact injuries were combined. ACL injury prevention programs are designed to prevent noncontact injuries and are especially relevant for high-risk sports such as soccer and basketball.


  1. Hewett, T.E.; Stroupe, A.L.; Nance, T.A.; Noyes, F.R. Plyometric training in female athletes. Decreased impact forces and increased hamstring torques. Am J Sports Med 1996, 24, 765-773.
  2. Noyes, F.R.; Barber-Westin, S.D. Neuromuscular retraining intervention programs: Do they reduce noncontact anterior cruciate ligament injury rates in adolescent female athletes? Arthroscopy 2014, 30, 245-255.
  3. Mandelbaum, B.R.; Silvers, H.J.; Watanabe, D.S.; Knarr, J.F.; Thomas, S.D.; Griffin, L.Y.; Kirkendall, D.T.; Garrett, W., Jr. Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes: 2-year follow-up. Am J Sports Med 2005, 33, 1003-1010.
  4. Labella, C.R.; Huxford, M.R.; Grissom, J.; Kim, K.Y.; Peng, J.; Christoffel, K.K. Effect of neuromuscular warm-up on injuries in female soccer and basketball athletes in urban public high schools: Cluster randomized controlled trial. Arch Pediatr Adolesc Med 2011, 165, 1033-1040.
  5. Kiani, A.; Hellquist, E.; Ahlqvist, K.; Gedeborg, R.; Michaelsson, K.; Byberg, L. Prevention of soccer-related knee injuries in teenaged girls. Arch Intern Med 2010, 170, 43-49.
  6. Walden, M.; Atroshi, I.; Magnusson, H.; Wagner, P.; Hagglund, M. Prevention of acute knee injuries in adolescent female football players: Cluster randomised controlled trial. BMJ 2012, 344, e3042.

First Course to Kick Off 2015

We kicked off our 1st certification course of 2015 with 5-8 inches of snow! Remarkably all of our course participants made it safely without delays or cancellations, traveling from Pennsylvania, New York, Wisconsin, Nebraska, Minnesota and New Mexico!  Perhaps the most difficult trip came for the two traveling the shortest distance…Erich Koenig and Ashley Stanko from Dayton Children’s Hospital drove through snow and ice early Saturday morning and made it on time! Thanks to all of you for your dedication and commitment to Sportsmetrics and injury prevention!  We welcome 12 new members to the Sportsmetrics team:

Craig Allen, ATC:  OSR Physical Therapy, Chaska, MN

Katelyn Dahl, DPT:  OSR Physical Therapy, Minnetonka, MN

Megan Freeman, DPT:  Proformance Physical Therapy, Lincoln, NE

Kurt Jacobson, ATC:  Mayo Clinic Health System, Eau Claire, WI

Erich Koenig, ATC:  Dayton Children’s Hospital, Dayton, OH

Jeffrey Lasko, PT, CSCS:  ACMH Hospital, Sarver, PA

Felipe Mares, PT:  PT First, Albuquerque, NM

Nicole Nolan, DPT:  Sports Physical Therapy of New York, Rochester, NY

Amy Postupack, PT:  ACMH Hospital, Lower Burrell, PA

Allison Pulvino, PT:  Sports Physical Therapy of New York, Rochester, NY

Ashley Stanko, ATC, MBA:  Dayton Children’s Hospital, Dayton, OH

David Webster, ATC:  Mayo Clinic Health System, Eau Claire, WI

TAI Web Course

On November 1st and 2nd, we held a web course for Therapeutic Associates (TAI) in Portland, OR.  Throughout the years we have held one private course for TAI in Bend, OR in 2005 and one additional web course hosted at their Hillsboro, OR location in 2010.  We have certified over 40 of their therapy staff making TAI one of our largest certified sites.  We hope to continue to build our relationship with TAI and thank them for making such a strong commitment to ACL injury prevetion.  We welcome the new TAI-Sportsmetrics certified staff:

Kristen Allison, ATC:  TAI Grants Pass Physical Therapy

Victoria Bryson, PT, DPT, CSCS:  TAI Sherwood Physical Therapy

Alissa Cameron, PT:  Proactive Orthopedic & Sports Physical Therapy

Laura Evans, PT, DPT, OCS:  TAI Sherwood Physical Therapy

Angela Lewis, PT, DPT:  TAI Crescent Village Physical Therapy

Samantha Marikis, DPT:  Apex Physical Therapy

John Nielsen, PT, DPT, OCS:  TAI OMG-Country Club Road

Kelly Reed, PT, COMT, OCS:  TAI Cedar Hills Physical Therapy

Jay Ruettgers, PT, DPT, ATC, CSCS:  TAI Medford Physical Therapy

Cliff Stanford, PTA:  Proactive Orthopedic & Sports Physical Therapy

Lonnie Swenson, MS, ATC/L, CSCS:  3D Sports Performance LLC

Belen Vala-Haynes, PT, DPT, OCS:  TAI NE Portland

Jason Zhao, PT, DPT:  TAI Bethany PT

November 15-16 Course

Our November 15th – 16th course was full of surprises that kept us on our toes, including a power outage and a very long and COLD evacuation due to a false fire alarm.  I guess there is a first time for everything and two of ours fell on the same day!  Nevertheless, our course participants showed great resilience and were ready to tackle the course with enthusiasm.  We promise, we are looking for a battery-powered projector!  It ended up being a great weekend and we would like to  welcome and say thank you to the newest editions to the Sportsmetrics community:

Alexa Amato, SPT:  Grand Island, NY

Danielle Baldwin, ATC: Spectrum Health Medical Group Sports Medicine, Grand Rapids, MI

Cole Brooks, PTA: North Platte Physical Therapy, Cheyenne, WI

Derrick Campbell, PT:  Texas Orthopedics Sports & Rehabilitation Association, Austin, TX

Matt Connell, MPT, ATC:  Arlington Physical Therapy, LLC, Arlington, TN

Kristen Crea, ATC, LAT, ITAT:  Gwinnett Medical Center, Duluth, GA

Anthony Eshleman, DC:  Shelby Chiropractic Health Center, INC, Sidney, OH

Ashley Feeney, ATC, LAT, ITAT:  Gwinnett Medical Center, Duluth, GA

Robert Ferguson, BS, CSCS, CPT:  McHenry County Orthopaedics, Crystal Lake, IL

Rebecca Fournier, DPT:  Children’s Therapy Group, LLC, Cheyenne, WY

Justin Greenlaw, ATC:  Spectrum Health Medical Group Sports Medicine, Grand Rapids, MI

Benjamin Hagge, ATC:  Spectrum Health Medical Group Sports Medicine, Grand Rapids, MI

Bradley Holland, PT:  Northeastern Health System, Tahlequah, OK

Michael Humphrey, PT:  McHenry County Orthopaedics, Crystal Lake, IL

Simon Ibrahim, PTA, CIMT, CEAS:  Benchmark Physical Therapy, Ooltewah, TN

Justin Jones, MS, CSCS, USAW:  Carolinas Healthcare System Rehabilitation, Charlotte, NC

Kelly Kamarad, DPT:  Children’s Therapy Group, LLC, Cheyenne, WY

Jeanethe King, ATC:  Buffalo, NY

Michelle Krings, MS, PT, ATC:  ATI Physical THerapy, Northville, MI

Marion Lake, PT:  Texas Orthopedics Sports & Rehabilitation Association, Austin, TX

Carey Lam, PT, MS:  Children’s Therapy Group, LLC, Cheyenne, WY

Matthew Lang, MA, ATC:  Spectrum Health Medical Group Sports Medicine, Grand Rapids, MI

Ashley Miller, PT:  Middle Tennessee Bone & Joint Physical Therapy, Columbia, TN

Brent Morrow, DPT:  Flagstaff, AZ

Luke Murray, ATC:  Spectrum Health Medical Group Sports Medicine, Grand Rapids, MI

Bryan Olding, DC:  Shelby Chiropractic Health Center, INC, Sidney, OH

Eilish O’Sullivan, PT, DPT, OCS:  Hospital for Special Surgery/Centurian Physical Therapy, New York, NY

Tori Rosenthal, DPT:  Children’s Therapy Group, LLC, Cheyenne, WY

Megan Snow, MA, ATC: Spectrum Health Medical Group Sports Medicine, Austin, TX

Tanisha Wheatley, BS, SPT: Saltsburg, PA

Shane Wilson, PT, ATC: Middle Tennessee Bone & Joint Physical Therapy, Columbia, TN

Caitlin Wright, ATC:  Spectrum Health Medical Group Sports Medicine, Grand Rapids, MI

October 4-5 Certification Group

On October 4th and 5th, we held a smaller group certification course for 11 healthcare professionals throughout the country. Physical therapists and athletic trainers came from Georgia, Ohio, Louisiana, Michigan, New York and Texas to learn how to prevent ACL injuries in their communities.  Unfortunately, our course attendees missed the beautiful fall weather we were having here in Cincinnati and instead were welcomed with rain and falling temperatures.  I guess it was a good weekend to stay instead and soak up some knowledge.  Our smaller groups really give us a chance to understand our individual certified sites’ needs and interests in the program and makes it easier to set up a marketing and roll-out strategy for each site.  We enjoyed the weekend and welcome the newest editions to the Sportsmetrics community:
Cody Burrough, PT:  San Marcos, TX

Kadi Carmosino, DPT:  Cincinnati SportsMedicine, Cincinnati, OH

John Connolly, DPT, CSCS: Armonk Physical Therapy and Sports Training, Armonk, NY

Dean Cross, PT:  San Marcos, TX

Tiina Garrison, PhD:  Alexandria, LA

Andrew Green, DPT, ATC:  Sports Physical Therapy of NY, Liverpool, NY

Greg Hollenbeck, DPT:  Daemen College, Lockport, NY

Katherine Hrisoulis, DPT:  Team Rehabilitation, Macomb, MI

Kristen Schuman, DPT:  Cincinnati SportsMedicine, Cincinnati, OH

Colin Sutton, PT:  Gwinnett Medical Center, Duluth, GA

Matthew Sweet, MS, ATC, PTA:  Sports Physical Therapy of NY, Liverpool, NY

Emeryville Sports Physical Therapy Private Course

On July 26-27, Sportsmetrics traveled to Emeryville, CA to host a private course with Robert Baker and his sports medicine colleagues in the San Francisco area. We would like to thank Bob for inviting us and the entire Emeryville group for making it a course to remember.  We would like to welcome our newly certified instructors to the Sportsmetrics family:

Chelsea Anjeski, PT, DPT:  Emeryville Sports Physical Therapy, Emeryville, CA

Robert Baker, PT, OCS:  Emeryville Sports Physical Therapy, Emeryville, CA

Jonathan Cabrera, BS:  Emeryville Sports Physical Therapy, Emeryville, CA

Heather Cramer, MS, ATC:  El Dorado Physical Therapy, Folsom, CA

Susanne DeCosterd, MPT:  Terra Linda Sport & Physical Therapy, San Rafael

Tricia Fong, MSPT, COMT: The Stone Clinic, San Francisco, CA

Robin Hamilton, DPT, OCS:  Emeryville Sports Physical Therapy, Emeryville, CA

Susana Hodgers, DPT, CSCS:  The Stone Clinic, San Francisco, CA

Laura Keller, MPT:  The Stone Clinic, San Francisco, CA

Reuben Zuniga, ATC:  El Dorado Physical Therapy, Folsom, CA

July 19-20 Certification Group

On July 20th, we held a certification course in Cincinnati, OH and certified 28 healthcare professionals in 13 states and the US Virgin Islands.  We welcome our new certified instructors and thank you all for your dedication to knee injury prevention!

Gretchen Aberg:  Mercy HealthPlex, Cincinnati, OH

Mary Bauer, LAT:  Mayo Clinic Health System, Eau Claire, WI

Maritza Benito, DPT:  Virgin Island Orthopedics, St. Thomas, VI

Erika Berens, ATC:  Barrett Hospital & Healthcare, Dillon, MT

Wayne Burns, AFAA certified:  Fortified Fitness, Murfreesboro, TN

Clay Case, PT student:  Daemen College, Lockport, NY

Kari Curry, intern:  Cincinnati SportsMedicine, Cincinnati, OH

Sylvia Czuppon, DPT, OCS:  Washington University Physical Therapy Clinics, St. Louis, MO

William Denz, PT student:  Daemen College, East Aurora, NY

Kimberly DePaul, PT:  In Motion Physical Therapy & Rehabilitation, Downingtown, PA

Edward Erickson, DPT, ATC:  Cincinnati SportsMedicine, Cincinnati, OH

Je’Ney Jackson, CSCS:  Indiana University, Bloomington, IN

Betty Jackson, PTA student:  North Platte Physical Therapy, Cheyenne, WY

Stephanie Wickstrom, LAT:  Mayo Clinic Health System, Eau Claire, WI

Thomas Kane, PTA, CPT:  Harrisburg, PA

Matt Kanetzke, intern:  Cincinnati SportsMedicine, Cincinnati, OH

Dustin Malandra, CSCS:  Cabrini College, Radnor, PA

Cassie Metze, DPT:  Cincinnati SportsMedicine, Cincinnati, OH

Trisha Miller, ATC:  Excel Sports Medicine, Springfield, OH

Alysse Morgan, DPT:  Total Rehab, Durant, OK

Jimmy Phillips, PT, ATC:  Tennessee Orthopedic Alliance, Murfreesboro, TN

Kearsten Renzi, PT student:  Daemon College, Williamsville, NY

Michael Stewart, DPT:  Lattimore Physical Therapy, Rochester, NY

Gary Tayag, PT:  UMC Team Rehab @ Zach’s Club on Milwaukee, Lubbock, TX

John West, MS, MD:  Peace Health, Riverbend Hospital Pavilion, Springfield, IL

Willie Yuen, DPT:  Performance Rehab, Overland Park, KS

Susan Zhang, PT:  Battle Creek, MI