A Meta-Analysis to Determine if Lower Extremity Muscle Strengthening Should Be Included in Military Knee Overuse Injury-Prevention Programs

Abstract

Context: Knee overuse injuries are the most common musculoskeletal complaints in military trainees and are common in active-duty warfighters. Muscle strengthening is usually recommended; however, research is conflicting in this area, which makes it difficult to develop effective screening, prevention, and training interventions for warfighters.

Objective: To determine if lower extremity muscular weakness contributes to knee overuse injuries and identify specific muscular involvement.

Data sources: We searched MEDLINE, PubMed, Web of Science, SPORTDiscus, CINAHL, and Military & Government Collection and reference lists of relevant articles published between January 1, 2000, and January 1, 2013.

Study selection: For inclusion, requirements were uninjured and injured groups; provision of the sample size, means, and standard deviations for all groups; identification of the specific muscles assessed; and clearly defined knee injury.

Data extraction: Sample size, sex, and muscle strength means and standard deviations.

Data synthesis: Twenty-five studies met these criteria. We used the Scottish Intercollegiate Guidelines Network algorithm to determine the appropriate tool for appraising article quality. Unweighted random-effects model meta-analyses were conducted. Separate meta-analyses were performed for the moderators of strength measurement scale (absolute or normalized muscle strength), muscle group, and sex. A weighted random-effects model with a Hedges g effect metric and 95% confidence intervals were used for comparison across studies.

Conclusions: Our meta-analysis suggests that individuals with symptoms of a knee overuse injury have lower absolute and normalized hip muscle strength. Specifically, they had lower absolute hip external-rotator, knee-extensor, and knee-flexor strength, as well as lower normalized hip external-rotator, hip-extensor, and hip-abductor strength, compared with asymptomatic control participants. The findings suggest a possible link between lower hip and thigh strength and knee overuse injuries. Further research is needed to determine if weakness is a cause or a result of knee overuse injuries before screening and intervention can be developed for at-risk warfighters.

Keywords: hip strength; iliotibial band syndrome; patellofemoral pain syndrome; warfighters.

Figure 1.

Funnel plot of included studies.

Figure 2.

Outline of literature search and selection.

Figure 3.

Forest plot of overall absolute strength and moderated analyses. ^a Indicates difference (P ≤ .05).

Figure 4.

Forest plot of overall normalized strength and moderated analyses. ^a Indicates difference (P ≤ .05).

Figure 5.

Forest plot of ratio strength. ^a Indicates difference (P ≤ .05).