ABOUT THE KNEE: The knee is made up of three bones designed to produce smooth, stable motion: the shinbone (tibia), the thighbone (femur) and the kneecap (patella). The bones are enclosed in the joint capsule, which is lined with a tissue that produces a thick liquid to keep the joint lubricated and nourished. The knee is kept in alignment by ligaments and tendons. The anterior cruciate ligament (ACL) is one of two major stabilizing ligaments of the knee joint. The other one starts at the back of the knee -- the posterior cruciate ligament. These two ligaments cross each other at the center of the knee. There is another set of stabilizing ligaments on either side of the knee as well, which stabilize the joint when the knee moves from side to side.
WHEN GOOD JOINTS GO BAD: A healthy knee bends easily, absorbs stress and glides smoothly so that we can walk, squat, or turn without pain. When the knee is damaged, it is less able to handle stress, causing pain and swelling. Injuries to the ACL are the most common. Often there is a loud "pop" -- the sound of the ligament tearing --followed by pain and immediate swelling. After those symptoms subside, the patient may still experience episodes of instability, often likened to walking on roller skates. The knee may feel loose. In serious cases, surgical repair may be required.