Numerous studies on meniscal tears have been published, a pathology that continues to evolve in terms of treatment and patient outcomes. As our understanding of anatomy and biomechanics improves, new entities have emerged. The lateral meniscus, especially its posterior attachment, tends to be overlooked due to its greater mobility compared to the medial meniscus. Evaluating the instability of the posterior horn poses a challenge, even during arthroscopy, therefore, it is crucial to understand the posterior menisco-synovial detachment lesions, which are indeed real and, to date, haven't received enough attention in the existing literature.The aim is to describe a new entity affecting the posterior synovial attachment of the lateral meniscus, without injury to the posterior horn of the lateral meniscus (PHLM). We also aim to present a case report detailing the intraoperative diagnosis and management of a 20-year-old patient with a sports trauma that led to a combined anterior cruciate ligament (ACL) and lateral meniscus tear managed with arthroscopic ACL reconstruction and all-inside meniscal suture.Through conventional arthroscopic evaluation of the posterior capsule anatomy and dissections, we have identified a distinct lesion of the PHLM at the menisco-synovial junction. Further research is necessary in this field to understand the biomechanical repercussions and determine the ideal surgical management.