Plunge into exercise, particularly any routines that stretch and strengthen the muscles, tendons, and ligaments surrounding your knee.

The sooner you get started, the better. If you rest your knee for more than 48 hours, the muscles and other tissues that stabilize the joint and help it keep it flexible will begin to weaken and atrophy. That, in turn, will aggravate your pain.

Weak quadriceps, for instance, can make it harder for you to control how hard your feet hit the ground as you walk and can increase the strain on your knee and hasten the breakdown of cartilage within the joint.

But simple exercises that promote flexibility and strength will dampen your pain and help fend off further discomfort. In fact, preliminary data suggests that when 30 people with osteoarthritis of the knee followed an at-home strength-training program, they averaged a 37 percent reduction in pain and an 82 percent increase in strength of the affected leg. After 4 months, they were more active and confident, with fewer limps and hobbles.