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Competing Interests: The authors declare no conflict of interest.

Background: Cyclops syndrome after anterior cruciate ligament (ACL) reconstruction is due to a fibrous nodule that develops in the anterior part of the intercondylar notch and prevents full knee extension. The primary objective of this systematic literature review was to evaluate the incidence of symptomatic cyclops lesion after ACL reconstruction. The secondary objective was to identify risk factors for cyclops syndrome., Hypothesis: Cyclops syndrome is common after ACL reconstruction and has several risk factors reported in the literature., Methods: A systematic literature review was performed by searching the PubMed, Medline, CINAHL, Cochrane, and Embase databases with the key terms 'cyclops' and 'ACL reconstruction'. The data thus retrieved were evaluated independently by two investigators. All articles in English or French that reported the incidence and risk factors of cyclops syndrome after ACL reconstruction were included., Results: The search retrieved the titles and abstracts of 79 articles, of which 20 were selected to be read in full; among these, 10 were included in the study. The incidence of symptomatic cyclops lesion ranged from 1.9% to 10.9%. Identified risk factors were as follows: pre-operatively, knee inflammation and/or motion restriction at the time of ACL reconstruction; intra-operatively, narrow intercondylar notch and excessively anterior position of the tibial tunnel; and post-operatively, persistent hamstring muscle spasm., Discussion: Development of a cyclops lesion is common after ACL reconstruction, occurs early, and may require further surgery. The knowledge of the risk factors provided by this study may improve the ability to devise effective preventive measures., Level of Evidence: II, systematic literature review., (Copyright © 2019 Elsevier Masson SAS. All rights reserved.)