The Value of Knee Injury Prevention Programs

    A systematic review and meta-analysis of RCTs adds to the literature on the usefulness of programs to prevent knee injuries in soccer players, showing that these programs most likely aid in preventing ACL injuries.


    Svetlana Dani, MD, and Warren Young, MD


    Grimm, NL, Jacobs JC, Kim J, Denney BS, Shae KG. Anterior Cruciate Ligament and Knee Injury Prevention Programs for Soccer Players: A Systematic Review and Meta-Analysis. Am J Sports Med. 2014 Dec; 43 (8): 2049-2056.


    In a systemic review and meta-analysis of 9 high-quality randomized controlled trials (RCT), implementation anterior cruciate ligament (ACL) and knee injury prevention programs for soccer players were found to significantly reduce the risk of knee injury overall. However, reduction of the risk of ACL injuries was not statistically significant.

    The researchers conducted a systemic search of the literature and included studies with the following criteria:

    • Level 1 RTC
    • Injury prevention program specific to knee injuries and/or ACL injuries
    • Subjects were soccer players

    Knee injuries were defined as any trauma, whether contact, non-contact, acute and chronic, ligamentous or non-ligamentous in nature. Prevention techniques included strengthening, stretching, proprioception, and neuromuscular exercises.

    The studies were carefully assessed for internal validity, publication bias, and heterogeneity. Of the 3377 studies, 9 fit the inclusion criteria. The 11,562 total athletes in the 9 studies included 7889 being analyzed for ACL-specific injuries.

    Five studies included only females, 3 studies included only males, and 1 study included both males and females. Five studies reported on knee injury alone, and 4 studies reported on both ACL and knee injury.

    Seven of the 9 studies showed a protective effect of prevention programs against all knee injuries (relative risk <1). This finding was statistically significant in 2 of the 7 studies. The pooled effect of all studies reflected the findings of the individualized studies, with a statistically significant protective effect of preventative programs against all knee injuries.

    Three studies described a protective effect against ACL injuries specifically, but none of the studies were statistically significant. Predictably, the pooled analysis showed similar results, with a non-significant protective effect against ACL injuries with implementation of an injury prevention program.

    The internal validity (risk of bias) scores for all studies ranged from 5 to 9, with 11 being the highest possible score. None of the studies, whether reporting knee or ACL injuries, showed a publication bias based on several statistical tests with the exception of 1 test.

    The meta-analysis did not include subgroup analysis based on sex, skill level, or specific intervention type. Given the small sample size (9 studies), such additional analysis could have lent itself to type I error.

    The strength of this meta-analysis is the inclusion of only Level 1 RCTs. It is the first study to do so, as all other published systematic reviews and meta-analysis have included both RTCs and non-randomized studies.

    The inclusion of RCTs only prevents exaggeration of treatment and introduction of bias, effects common to non-randomized trials.

    In addition, all studies used were specific to a single sport, allowing the results to be generalizable to an athletic population.

    The authors noted the limitation of the study was not blinding the reviewers who chose the included articles. One of the authors had previously participated in a study of knee injury prevention in female athletes, which could introduce selection bias.

    In addition, given the small sample size of 9 studies, publication bias may be difficult to assess.

    Clinical Relevance

    Soccer is an extremely popular sport, with significant participation around the world. Most soccer-related injuries involve the lower extremities, especially the knee.

    Female soccer players have a 3 to 5 times higher risk of serious knee injury compared with male soccer players. Knee injuries, especially ACL injuries can cause prolonged time away from sports activity. In addition, ACL tears are related to a high percentage of permanent disability.

    Several studies have focused on techniques for preventing these knee injuries. Such studies are difficult to design, expensive, and time-consuming. Subsequently, they have yielded mixed results.

    ACL prevention programs have also been discussed, and recommendations for these programs have been published recently by several organizations, including the AAP Council on Sports Medicine in Fitness in May 2014 and the AAOS Appropriate Use Criteria in October 2015.

    Most published recommendations are in agreement that such prevention programs are useful for adolescent females in high-risk sports such as soccer.

    This study by Grimm et al is the first systemic meta-analysis of the best-designed studies in prevention techniques against knee/ACL injuries.

    The researchers vigorously tried to exclude all possible bias to come to the most objective conclusion. Although there are limitations as discussed above, this study adds to the discussion that such programs are useful prevention of knee injuries in general, and most likely also to preventing ACL injuries.

    ACL injuries are the most frequently reason for implementing a prevention program. However, when promoting these programs, clinicians should emphasize that other knee injuries can also be prevented.

    In addition, the paucity of studies that met the strict inclusion criteria of this meta-analysis suggests the need for further high-quality research.

    Author Information

    Svetlana Dani, MD, is a resident in the Department of Pediatrics at NYU School of Medicine/NYU Langone Medical Center, New York, New York. Warren Young, MD, is an Assistant Professor of Orthopaedic Surgery, Division of Primary Care Sports Medicine, Department of Orthopaedic Surgery, NYU Langone Medical Center – Hospital for Joint Diseases, New York, New York.