Behind my left knee hurts constantly. my orthopedic specialist thinks its maybe baker cyst. how do we know?

Ultrasound: A bakers cyst can be seen on an ultrsound or mri. Posterior knee pain most commonly is casued by a bakers cyst, half of these are associated with a torn cartilage (torn meniscus). Posterior knee pain can also be caused by a back problem (sciatica) or vascular problem (aneurysm).

MRI or ultrasound: Mri or an ultrasound can demonstrate a baker's cyst. However, most baker's cysts are not painful but often occur when there is swelling joint in the knee for other reasons such as arthritis or a cartilage tear. Those are usually the causes of the pain, not the cyst.