Hi, thanks for writing to HCM.
Anastrozole is a Aromatase inhibitor
used in the treatment of breast cancer
in post menopausal women.
Anastrozole lowers the oestrogen levels in the body which will slow down the growth of certain breast tumours which needs oestrogen to grow. So Anastrozole indirectly causes decreased bone mineral density which inturn causes osteoporosis
leading to bone and joint pains.
Your knee joint pain could also be attributed to Osteoarthritis
which is common at your age.
Hope this information is helpful. Good day