METHODS: This was a 21-year-old male patient who suffered a knee injury (swelling and pain) playing football. A physical examination revealed positive Lachman and lateral McMurray tests. MRI images showed an ACL injury and the flag sign, and a diagnosis of ACL tear and lateral meniscal injury was made. Arthroscopic lateral meniscal repair and ACL reconstruction were performed. Six months postoperatively, MRI showed that the injuries were well healed. In this particular case, the flag sign introduced interference to the MRI assessment of ACL injury.
CONCLUSIONS: This case illustrates that clinicians should carefully identify the morphological changes in the meniscus and the relationship of the meniscus with the femoral condyle before reaching a final diagnosis.