I am 46 and have had menstrual cycle for 1 1/2 weeks I had a knee replacement in may and I just started haveing menstrual cycles in july but this is the longest one.

It depends. After total knee surgery, due to the stress of surgery an blood loss it is not unusual to have changes in the menstrual cycle both frequency and duration as well as intensity of bleeding can be affected. But having said that if you are concerned it is prudent to contact your gynecologist to let him/her check to make sure you do not need d;c.
Are . Are you on any blood thinner type medications? If so then please notify your doctor of this long period. A period lasting this long can occur from hormonal imbalance and can be caused by perimenopause also. Please be sure that your pap smears are up to date. If you have heavy bleeding you might also need an endometrial biopsy. If this continues or you have new symptoms, please have a medical evaluation.