Knee Morphological Risk Factors for Anterior Cruciate Ligament Injury
Authors: Bayer Steve , Meredith Sean J. , Wilson Kevin W. , de SA Darren , Pauyo Thierry , Byrne Kevin , McDonough Christine M. , Musahl Volker 
Published: January 2020

Update
This article was updated on June 9, 2020, because of previous errors. On pages 703 and 716, in the byline section and author affiliation section, “Kevin Wilson” now reads “Kevin W. Wilson,” “K. Wilson” now reads “K.W. Wilson,” and “Kevin Wilson, MD2” now reads “Kevin W. Wilson, MD3.” The affiliation for Dr. Wilson that had read “2Department of Orthopaedics, University of Maryland School of Medicine, Baltimore, Maryland” now reads “3Department of Orthopaedic Surgery, Mount Nittany Health, State College, Pennsylvania” with affiliations 3 through 6 renumbered as 4 through 7.
An erratum has been published: J Bone Joint Surg Am. 2020 Jul 15;102(14):e85.

Background:
Anterior cruciate ligament (ACL) reconstruction incidence has increased substantially in the past 25 years. Recently, there has been a focus on knee morphology as a contributor to ACL injury risk. The purpose of this study was to systematically review the literature to assess the influence of knee morphology on ACL injury.

Methods:
In accordance with PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, PubMed, Embase, and MEDLINE were searched in September 2017 for studies reporting on knee morphology and ACL injury. The search was updated in June 2018. The following inclusion criteria were used: English language; full text available; Level-I, II, or III evidence; human studies; and skeletally mature patients.

Results:
After systematically screening 6,208 studies, 65 studies met the inclusion/exclusion criteria. Three additional studies were identified in the search update, for a total of 68 studies comprising 5,834 ACL-injured knees. Intercondylar notch stenosis, most commonly defined by an “A-shaped” notch, decreased notch width, or decreased notch width index, was the most commonly reported femoral morphological risk factor for ACL injury. Increased femoral condylar offset ratio (>63%) and decreased condylar radius of curvature also were associated with an increased risk of ACL injury. Increased medial and lateral tibial slopes were the most commonly reported tibial risk factors. A smaller tibial eminence, reduced ACL size, and poor tibiofemoral congruity were also associated with increased injury risk.

Conclusions:
Intercondylar notch stenosis, variations in sagittal condylar shape, increased tibial slope, reduced tibial eminence size, poor tibiofemoral congruity, and reduced ACL size are substantial risk factors for ACL injury. In future research, it would be valuable to identify a slope beyond which slope correction should be performed concomitantly with ACL reconstruction, and to determine whether an optimal relationship of notch size to graft size exists. To achieve optimal outcomes, the osseous morphological risk factors should be considered in individualized anatomic ACL reconstructions.

Level of Evidence:
Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.