I am a 71 year old female & have osteopenia. I ve had a compression fracture in my spine after my 100 lb. dog (playfully) knocked me off my feet. My doctor has suggested that I start taking Fosamax. I understand in rare instances, Fosamax is associated with fracture in the femur. I have had both knees replaced--my left knee was especially bad and the surgeon said he had to make the new knee components longer to go deeper into my bones than usual, although I think he was talking about the lower part of the leg. Given the knee problem, is it wise to start Fosamax, or would some other drug be better?