1 Introduction

The reported incidence of isolated anterior cruciate ligament (ACL) tears is 68 per 100,000 person-years, corresponding to over 200,000 ACL injuries in the United States per year.¹ Over half of individuals who experience an ACL injury elect to undergo reconstruction (ACLR) surgery.^2,3 Following ACLR, reported success rates based on return to preinjury level of sport range from 59% to 72 %.⁴ Factors associated with successful return to preinjury level include patient age <21 years, male sex, elite-level athlete, and patient-reported positive psychological responses regarding emotions, confidence, and future risk appraisal.^4,5,6 In a recent systematic review, risk for re-tear after ACLR was reported to be 5.8 %.³ Risks for ipsilateral reinjury include age <25 years, Marx activity score ≥13⁷, and ACLR using hamstring tendon autograft.⁸ While these and numerous other variables have been assessed for their associations with outcomes after ACLR, the impact of factors related to social determinants of health (SDOH) following ACLR have not been well characterized.

SDOH are categorized into 5 domains, including economic stability, education access and quality, health care access and quality, neighborhood and built environment, and social and community context.⁹ Each domain represents a group of factors that influence an individual's overall health.¹⁰ In orthopaedics, the impacts of SDOH have primarily focused on arthroplasty. For example, black race, education level less than high school, and household income below the poverty level have been reported to be associated with worse Oxford Hip and Knee scores following total knee and total hip arthroplasty.¹¹ In addition, SDOH including ethnicity, educational level, poverty level, and income were noted to be more important than implant factors in predicting the presence of thigh pain, dissatisfaction, and Harris Hip Score less than 90 following total hip arthroplasty.¹² Based on this evidence for outcomes after arthroplasty, characterizing the influence of factors related to SDOH on outcomes following ACLR is important for optimizing patient care. As such, the objective of this study was to review and synthesize current literature to determine the impact of SDOH on outcomes following ACLR. Our overarching goal for this research is to characterize the impacts of SDOH on outcomes after ACL injury and reconstruction toward development and implementation of patient-centered evidence-based management strategies to better equip patients for successful and satisfying outcomes.

2 Methods

This review was registered with PROSPERO (CRD42022299789) and conducted using the PRISMA protocol. A systematic search of PubMed, CINAHL, Medline, PsychINFO, SCOPUS was performed for all publications from inception to November 2021 available in the English language. Search terms included ACL, anterior cruciate ligament, Social Determinants of Health, socioeconomic factors, education, occupation, income, wealth, race, insurance, distance to facility, health literacy, and zip code. Inclusion criteria were determined a priori as follows.a)Did the article provide failure/ACLR revision information for the study population?b)Was at least one social determinant of health reported?

There was no requirement for publication date or population age. Only studies available in English were included.

The study title and abstract were screened by three independent reviewers (LT, AV, KR), with disagreements resolved through direct conversation until a definitive conclusion regarding inclusion could be made. Data extraction was as follows: ACLR failure incidence, patient reported outcomes when available (Knee Injury and Osteoarthritis Outcome Score (KOOS Jr) and International Knee Documentation Committee (IKDC)), SDOH measured, revision rate, and post-surgical complications. Failure was defined as clinical confirmation of a torn or nonfunctional ACL graft, and/or revision ACLR. (See Fig. 1, PRISMA Flow Diagram).

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Fig. 1 PRISMA flow diagram.

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Level of Evidence: Level of evidence was evaluated for all included studies. Eleven studies were level 3 case-control or retrospective studies, and two studies were level 2 prospective or cohort comparative studies (Table 1).

Bias was ascertained for all included studies by two reviewers independently (LT, AV) using the Risk of Bias in Non-randomized Studies – of Exposures (ROBINS-E) tool. The third reviewer (KR) analyzed findings, resolved disagreements, and assigned a final score for each of the 7 included domains. Risk of Bias (Table 2): Two of the thirteen articles were determined to have low to some bias, while the other 11 had at least one domain with high bias. In general, bias was high primarily due to missing data or failure to control for confounding variables.

3 Results

The primary search identified 1540 articles published through November 2021, and after duplicates were removed, 712 remained. Of the remaining articles, 12 met inclusion criteria. Once reference lists were examined, 1 additional study was included such that 13 articles were included for final analysis and synthesis (Table 1).

Studies included in the present review identified five SDOH that impacted outcomes following ACLR. Overall due to inconsistencies in study design and outcome measures reported a meta-analysis was not possible.

4 Discussion

This systematic review of the impacts of social determinants of health on outcomes following ACL reconstruction produced only a small number of qualifying peer-reviewed articles, which assessed race, income, location, education, and insurance variables. Based on the synthesis of qualifying articles, available evidence suggests that revision ACLR is reported to occur most commonly for white patients and those living in urban locations, while lower education level is reported to be associated with inferior long-term IKDC scores. However, level of evidence was moderate, risk for bias was high, and none of the qualifying articles analyzed support systems, provider availability, patient housing and transportation, or health literacy. As such, further research is critical for accurately assessing the effects of SDOH on outcomes after ACLR to make valid and clinically applicable conclusions and recommendations.

The most robust evidence from this systematic review regarding the impacts of SDOH on ACLR outcomes centered on race. White patients consistently had higher risk for revision ACLR when compared to non-white patients, though causal factors for this disparity were not clearly identified.^23,20,19,16 Because most studies used revision rate as the determinant for ACL failure, it is unclear if total re-tear rates are higher in white populations or if white patients are more likely to undergo surgery to address a re-tear. Interestingly, even in a universally insured cohort, white patients were more likely to undergo revision ACLR when compared to other races.¹⁶ Another possibility for this race-based difference may involve risk for ACL injury. Incidence for primary ACL injury is consistently reported to be higher in the white population compared to the non-white population.^28,29 However, causal factors for this predisposition to ACL injury in the white population have not been clarified to date, and because most studies typically utilize only white vs. non-white groupings, the incidence of ACL injuries in other subsets of race are unclear. Therefore, further research designed to characterize the causal impacts of race on ACLR outcomes need to consider the causal factors for race-based predisposition to ACL injury.

As documented in other areas of health care, systematic review of the literature focused on ACLR suggests that the impacts of SDOH on related outcomes are interconnected. For example, education level, income status and health literacy are strongly correlated.^30,18,31 In review of ACLR outcomes, an interconnection with educational status on outcomes warrants further investigation. Individuals with lower levels of education are more likely to work physically demanding jobs,³² lack resources for post-operative support,³³ and utilize tobacco products,³³ all of which could contribute to risk for complications following ACLR. As such, it is imperative that these findings are interpreted in context and that future studies include the impacts of interconnections of SDOH on outcomes such that barriers to optimizing care can be accurately identified and comprehensively addressed.

The main limitation to this study was the lack of qualifying peer-reviewed articles assessing the impacts of social determinants of health on outcomes following ACLR. In addition, level of evidence for qualifying studies was moderate with confounding variables, bias, potential for under-reporting, and lack of completeness of targeted assessments further limiting conclusions and applications. Even so, influential associations for SDOH and outcomes following ACLR were documented, revealing important considerations for healthcare teams. Patients with risk-factors for suboptimal outcomes following ACLR should be identified early, with protocols in place to address disparities and barriers. For example, patients with a lower education level should be provided with pre- and post-operative instructions at a 5th grade reading level, with adequate time provided for teach-back and question-answer opportunities.^34,35 For patients that live in rural communities or who face socioeconomic barriers, attention should be paid to equipping patients for effective home care and/or telehealth access and capabilities.^36,37,22 Best current evidence suggests that identifying and addressing these and other modifiable risk factors for failure after ACLR can significantly mitigate complications and improve outcomes for treatment of this common orthopaedic injury.

5 Conclusion

The results of this systematic review suggest that risk for revision ACLR is highest in white patients and those living in rural communities, with decreased function scores for patients that have lower education levels. These findings suggest that SDOH play key roles in outcomes following ACLR such that further research is needed to better elucidate the degree of impact and interconnectedness of SDOH domains on ACLR patient outcomes. The gaps noted based on this systematic review highlight the need for large matched-cohort analyses that control for confounding variables and include re-injury, revision, and functional outcome measures, as well as qualitative studies that include the patients’ perspectives in identifying barriers and opportunities to address SDOH-related risk factors for sub-optimal outcomes. Addressing these identified gaps in evidence will allow healthcare teams and healthcare systems to create solutions that provide equitable opportunities for successful outcomes following ACLR.

Ethical statement

Not applicable.

Funding statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Guardian/patient's consent

Not applicable.

CRediT authorship contribution statement

Luke Troyer: Conceptualization, Investigation, Methodology, Writing – original draft, Writing – review & editing. Aaron Voshage: Conceptualization, Investigation, Methodology, Writing – original draft, Writing – review & editing. Kylee Rucinski: Conceptualization, Investigation, Methodology, Supervision, Validation, Writing – original draft, Writing – review & editing. Steven DeFroda: Conceptualization, Methodology, Supervision, Writing – review & editing. James L. Cook: Conceptualization, Methodology, Project administration, Supervision, Writing – review & editing.