I had major back surgery and knee surgery on both knees. will i physically be able to have a baby?

Probably: Although your specific case should be discussed with your own surgeons, the vast majority of patients who have knee and major back surgeries can have normal pregnancy. To give you an example in my own practice, i routinely perform several hour scoliosis surgeries on young women in which screws and rods are inserted to straighten out the spine, and pretty uniformally have no problem with pregnancy.

Yes: Those problems and treatments, in and of themselves, do not prevent a normal, happy pregnancy. Counseling on details is probably very important.