Multiple pea sized lumps on tendon (or ligament!) behind knee that seem to travel up to the thigh, what might they be?

Bakers Cyst: A Baker's cyst is a common cause of a lump behind the knee. This condition develops when joint fluid leaks out from the joint cavity into the tissues behind your knee. Other causes include infections, bleeding, trauma, and, rarely, tumors. Bakers Cysts typically resolve on their own with rest of the affected limb. Avoid stretching, active exercise and straining muscles for 1-2 weeks.