The knee is a hinge. It is a large, weight-bearing joint, but the motion of the knee is much more strictly limited than that of most other joints. Knees straighten to make the leg a stable support, and it will bend to more than a right angle – to approximately 120 degrees. However, it does not move in any other direction. The great strength of the knee is from it's limited motion, but it is not engineered to take stresses on the side.

The knee must be stable and it must be able to extend fully to a straight leg. If it cannot extend fully the muscles must support the body at all times and knee strain is continuous. Normally our knee locks when in the straight position and allows us to relax. Weak knees that wobble from side to side cause too much stress on the side ligaments, and the condition may gradually worsen.

There are two cartilage compartments in the knee, the outer and the inner. If the cartilage does not wear evenly the leg will bow in or bow out, If you are obese you tend to be far more likely to have knee problems simply do to the additional load on the knee and the fluid membranes that cushion it.

If the knee cannot be straightened or is unstable and wobbles, you need to see the doctor. Similarly, you need a physician if there is a possibility of infection or gout. Finally, if you notice swelling or pain in the calf below the sore knee, you may have a blood clot, but more likely you have a “Baker cyst" either way you probably need to see a physician.

If you are experiencing knee pain, try not to do things that aggravate your knee. If there has been a recent injury, an elastic bandage may help; otherwise, probably not. Using a cane may help.

Do not use a pillow under the knee for any extended time such as at night or sitting, as this can make the knee stiffen so that it cannot be straightened out.

If you have knee pain do not do any weight bearing exercises without first consulting with your physician. Exercises should be started slowly and performed several times daily if possible. Swimming can be good because there is no weight-bearing requirement. From the beginning, pay close attention to flexing and straightening the leg. Having a friend help you move your leg through these motions may be more comfortable than doing it yourself at first. But work at getting it straight and keeping it straight. Next begin isometric exercises. Tense the muscles in your upper leg, front and back, at the same time, so that you are exerting force but your leg is not moving. Do this for two seconds, then rest two seconds. Do ten repetitions three times a day. Then begin gentle active exercises. A bicycle in a low gear is a good place to begin. Stationary bicycles work well.  Walking is probably the best overall exercise, and distances should be gradually increased. Don't do any deep knee bending exercises, as they place too much stress on the knee.

Make sure you are taking any prescribed medication as directed, since your painful knee could be caused by too little medication.