65 year old male has ridden his bike over heavy, mountainous terrain for over 30 years. He has noted increasing knee and hip pain in both legs. The doctor took Xrays and noted that there was significant breakdown of cartilage between the joints and his bones were rubbing together. The doctor diagnosed the man with _______________________.

A. Myalgia

B. Rheumatoid arthritis

C. Osteoarthritis

D. Osteoporosis