The knee is a hinge. It is a large, weight-bearing joint, but its motion is much more strictly limited than that of most other joints. It will straighten to make the leg a stable support, and it will bend to more than a right angle - to approximately 120 degrees. However, it will not move in any other direction. The limited motion of the knee gives it great strength, but it is not engineered to take side stresses.
There are two cartilage compartments in the knee, one inner and one outer. If the cartilage wears evenly the leg can bow in or bow out, or if you were born with crooked legs there can be strain that causes the cartilage to wear more rapidly. If you are overweight you are far more likely to have knee problems.
The knee must be stable and it must be able to extend fully to a straight leg. If it lacks full extension the muscles have to support the body at all times and strain is continuous. Normally our knee locks in the straight position and allows us to rest. Horses are able to sleep standing up because they can rest on their knees. If the knees wobbles from side to side there is too much stress on the side ligaments, and the condition may gradually worsen.
If the knee is unstable and wobbles or if it cannot be straightened out, you need the doctor. Similarly, you need a physician if there is a possibility of gout or infection; the knee is the joint most frequently bothered by these serious problems. Finally, if there is pain or swelling in the calf below the sore knee, you may have a blood clot, but more likely you have a "Baker cyst," you may need the doctor. These cysts start as fluid-filled sacs in an inflamed knee but enlarge though the tissues of the calf and may cause swelling quite a distance below the knee.
Try not to do things that aggravate the pain either immediately or the next day. If there has been a recent injury, an elastic bandage may help; otherwise, probably not. Using a cane may help. Most prefer to carry the cane in the hand on the side of the painful knee; some carry it on the opposite side.
Do not use a pillow under the knee at night or at any other time, as this can make the knee stiffen so that it cannot be straightened out.
Exercises should be started slowly and performed several times daily if possible. Swimming is 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 - passive exercise - 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. Exert the force 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 start. Stationary bicycles are fine. Be sure that the seat is relatively high; your knee should not bend to more than a right angle during the bicycle stroke. Walking is probably the best overall exercise, and distances should be gradually increased. Avoid exercises or activities that stimulate deep knee bends, as they place too much stress on the knee. Knee problems can come from the feet. Proper shoes can help to resolve this problem.
Make sure you are taking any prescribed medication as directed, since your painful knee could be caused by too little medication.
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