Tennis elbow (also known as lateral epicondylitis) can be the result of inflammation of the tendon where it inserts to the bone. Overuse or repetitive motion does cause an acute inflammatory response. Chronic tennis elbow may not have an active inflammatory process but it is still painful causing stifness, loss of strength, and loss of motion in some cases.
The same acute or chronic problems can occur at the knee when there is involvement of the patellar tendon. The patellar tendon attaches the quadriceps muscle along the front of the thigh to the bone below the knee cap. But patellar tendinitis (acute) or tendinosis (when it is chronic) is not the same as osteoarthritis (OA).
Knee OA is an active process of inflammation, swelling, and damage to the joint cartilage and joint surface. The treatment for these two conditions (tendinitis versus arthritis) is different. Although conservative (nonoperative) care is advised for both problems, surgery is more often needed for the knee arthritis.
If caught early enough, a simple debridement surgery (shaving and scraping the joint smooth) may be all that’s needed. More advanced stages of osteoarthritis may require a total knee replacement. Tennis elbow is never treated with a joint replacement but always conservative care.