When my Mother was 70, she had both of her knees replaced at the same time.
Lynn, there's a great knee (and hip) specialist out here in Cali. My Mother has never had a problem with her knees. He now has his own floor at the hospital staffed with his own people. His name is Dr. Dearborn and here is his website:
http://www.dearbornsah.com/
Great to hear from you Jan. Take care and let that shoulder (and you) rest and recover.