ORTHOPEDICS: Edited by Daniel GreenWhat is the J-sign and why is it important?Rousseau-Saine, Alexisa; Nault, Marie-Lyneb; Hiemstra, Laurie A.c,d Author Information aHôpital Maisonneuve-Rosemont bCHU Sainte-Justine, Université de Montréal, Montréal cBanff Sport Medicine, Banff dUniversity of Calgary, Calgary, Canada Correspondence to Laurie A. Hiemstra, Banff Sport Medicine, 213-300 Old Canmore Road, Canmore, AB T1W 0J5, USA. Tel: +1 403 760 2897; e-mail: [email protected] Current Opinion in Pediatrics 35(1):p 97-101, February 2023. | DOI: 10.1097/MOP.0000000000001193 Buy Metrics Abstract Purpose of review Recurrent lateral patellofemoral instability is a complex condition that requires a thorough evaluation to optimize treatment. The J-sign test is classically part of the physical examination, but its significance and importance remain unclear. This review aims to describe how to perform the test and classify the observation as well as to analyze the most recent literature on its clinical applications. Recent findings The J-sign test has been described as positive (present) or negative (absent), and classified using the quadrant method and the Donnell classification. Suboptimal inter-rater reliability has been shown for both classifications, making comparison between clinicians and studies challenging. The J-sign is most predominantly associated with patella alta, trochlear dysplasia, lateral force vector, and rotational abnormalities. A growing number of studies have shown a correlation between a positive J-sign and lower clinical outcome scores and higher rate of surgical failure. Summary The J-sign is an important aspect of the physical examination in patients with recurrent lateral patellofemoral instability. Although there is no consensus on how to perform or classify the test, it can be used as a marker of severity of patellofemoral instability and is one of the tools available to guide the treatment plan. Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.