What Causes Tearing Of The Anterior Cruciate Ligament And An Intra Articular Effusion/swelling?

MRI of the right knee shows a complete tear of the anterior cruciate ligament and an intra articular effusion/swelling. There is a
linear tear of the posterior horn of the lateral meniscus and complex tear of the anterior horn of the lateral meniscus. Linear signal consistent with degenerative change is noted in the medial meniscus but it does not extend to the meniscal surface.