Objective To determine sex-based differences in risk of a second ACL injury (overall and by laterality) following primary ACL reconstruction in athletes who are attempting to return to sport.
Design Systematic review with meta-analysis.
Data sources Systematic search of five databases conducted in August 2019.
Eligibility criteria for selecting studies Studies reporting sex-based differences in the incidence of second ACL injury in athletes attempting to return-to-sports and who were followed for at least 1 year following primary ACL reconstruction.
Results Nineteen studies were included in this review, with seven studies excluded from the primary meta-analysis due to high risk of bias. The remaining 12 studies (n=1431 females, n=1513 males) underwent meta-analysis, with all 19 studies included in a sensitivity analysis. Total second ACL injury risk was 21.9% (females: 22.8%, males: 20.3%). Females were found to have 10.7% risk of an ipsilateral ACL injury and 11.8% risk of a contralateral ACL injury. Males were found to have 12.0% risk of an ipsilateral ACL injury and 8.7% risk of a contralateral ACL injury. No statistically significant differences were observed for total second ACL injury risk (risk difference=−0.6%, 95% CI −4.9 to 3.7, p=0.783, I2=41%) or contralateral ACL injury risk (risk difference=1.9%, 95% CI −0.5% to 4.4%, p=0.113, I2=15%) between sexes. Females were found to have a 3.4% absolute risk reduction in subsequent ipsilateral ACL injury risk compared with males (risk difference=−3.4%, 95% CI −6.7% to −0.02%, p=0.037, I2=35%).
Conclusion Both sexes have >20% increased risk of experiencing a second ACL injury. Any difference in the absolute risk of either a subsequent ipsilateral or contralateral ACL injury between sexes appears to be small.
Registration PROSPERO (CRD42020148369)
- knee injuries
- sporting injuries
- knee surgery
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Twitter @DRGSBullock, @JayLos18
Contributors AP was first author on this paper; he conducted the screening for articles, conducted the data gathering, wrote the paper and edited the paper. GSB conducted statistical analysis of the paper, helped to write the paper, edited the paper and provided expertise on the subject matter. JW conducted the search for articles for the paper. MP edited the paper and provided expertise on the subject matter. TS initiated the paper topic, edited the paper and provided expertise on the subject matter. JL was principal investigator on this paper; he conducted the screening for articles, conducted the data gathering, helped write the paper, edited the paper and provided expertise on the subject matter. In addition, Leila Ledbetter, a contributor, provided guidance and assistance with generating the search and providing resources to optimise data management. All authors contributed to the writing, interpretation, critical revision and approval of the manuscript. AP, GSB, TS and JL conceived the research question. JW developed and executed the systematic literature search with input from JL, TS and GSB. AP, JL and GSB performed data extraction. GSB and JL performed statistical analysis and figure generation with input from TS and MP.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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