| If you think about it, the fact that many people have problems with their knees makes sense. We get all of our ability to walk, jump, turn, and crouch from the hinged joint that connects our thighs to our calves, and our knees have many different parts – cartilage, ligaments, tendons, muscles and bones – coming together at one point. If you factor in the obesity epidemic that has hit the United States over the past decades, that’s a lot of stress on many moving parts.
Most knee problems stem from injuries or disease. Most knee injuries happen when the knee receives impact or moves quickly and makes the knee move past its typical range of motion. Some injuries happen when other parts of the legs or back are hurt, and we change our gait as a result, moving the knee in new ways that cause stress over time.
The knee’s meniscus, or the crescent-shaped piece of soft tissue just beneath the kneecap, is vulnerable to twisting motions while carrying a heavy load, or while moving at high torque. Two frequent motions that cause meniscal tears or strains include turning quickly to avoid a tackle, or pivoting swiftly to hit a tennis ball.
There are two cruciate ligaments that snake through the knee: the anterior and posterior cruciate ligaments. The posterior (PCL) usually encounters injury from a direct hit, while the ACL (anterior) generally happens when the knee twists unexpectedly to an unusual degree.
There are also two collateral ligaments – the medial and the lateral. The medial gets injured more often than the lateral, but injuries to both collateral ligaments generally come from side impacts to the inside of the knee.
You can prevent knee injuries by stretching your quadriceps (front of the thigh) and your hamstring (rear of the thigh) before exercising, and by doing dynamic warm-up exercises such as riding a stationary bicycle or doing gentle lunges before running or other aerobic exercise.
As far as diseases go, the one occurring most frequently is arthritis, which can refer to a number of different inflammatory conditions that target the joints.
The two most frequently occurring types of arthritis are osteoarthritis and rheumatoid arthritis. Osteoarthritis occurs when, over time, the cartilage cushioning the knee during impacts degrades, resulting in greater bone-on-bone impact and changes in the shapes of those bones. If you have sustained a knee injury or are overweight, this is more likely to hit your knees, once you pass the age of fifty.
Rheumatoid arthritis tends to strike at a younger age, but has nothing to do with components wearing down. Instead, it stems from attacks by the immune system against the synovium, which lines the knees. These attacks cause swelling, which can break down all connective tissue and bone surrounding the knees.
 Other diseases that affect the knees include infectious arthritis, gout and psoriatic arthritis. Less common than the first two, these do cause significant amounts of pain and discomfort. Gout happens when uric acid ends up lodged in the joints instead of being flushed out of the system, and is usually the result of a very rich diet. Psoriatic arthritis involves inflamed joints in people who either have psoriasis or are developing it. Infectious arthritis involves joint swelling as the result of bacterial or viral infections.
If your knees chronically bother you, your primary care physician may send you to an orthopedist or a rheumatologist, depending on the situation. The orthopedist will get involved in cases of injury, and the rheumatologist will treat instances of arthritis and related diseases.
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