Why is the knee so vulnerable? In part it's because the knee has less mobility than many other joints. Take your foot and ankle, for example. The ankle-and-foot mechanism can move forward and backward, and also has some side-to-side motion. Your knee simply moves forward and backward like a hinge and can tolerate only very limited amounts of side-to-side or twisting motion. Therefore, whenever falls, collisions, or weird accidents occur that twist or wrench the knee, you are almost bound to end up with a knee injury.

Another reason your knee is so vulnerable is that it is a very intricate and complex mechanism with many parts that can go wrong. A person can have five or ten injuries at once in the knee. Very few people have perfectly aligned knees, but the slight deviations of alignment that so many of us have usually cause no problems. Sometimes, however, these slight deviations add up to an injury if you get involved in activities that are stressful on the knees, such as racket sports, skiing, running, basketball, or soccer.

Though the knee is complex, assessing knee injuries can be straightforward. The difficulty in assessment lies in the fact that people who have knee injuries often donıt get to the physicians and other health care practitioners who have expertise in this area. Often you can readily pinpoint the general location of the pain (e.g., in the front of your knee rather than the back) and in doing this you have already narrowed the possibilities down to four or five injuries. The exception is pain felt deep within the center of the knee. In these cases the cause of the injury is more elusive and difficult to figure out. Sometime knee pain can be referred form hip and back injuries. For instance, an irritation in the hip joint can cause a generalized pain in the front of the knee.

The knee joint is made up of the joining of the thigh (femur) and shin bone (tibia) with a small rounded bone in front called the patella or kneecap. The knee joint bends and straightens with a small twisting motion that isnıt apparent. The bones of the knee are held together by strong cords called ligaments. Two are strategically placed to prevent the bones of the knee from moving side to side. They are located at either side of the knee. The one on the inside, the medial collateral ligament, (A) prevents the knee from collapsing inward, and the outer one, the lateral collateral ligament (B) prevents the knee from collapsing outward. There are two ligaments, the anterior and posterior cruciate ligaments, (C and D) deep within the knee that prevent abnormal movement of the shin bone forward and backward.

Your knee has two types of cartilage. One is a thin, shiny, Teflon-like material (X), which coats the touching surfaces of all bones. This layer allows the bones to glide over one another easily. If this material wears away through a combination of misalignment and too much stress on the knee, it can cause long-standing arthritis in the knee, also called chondromalacia.

The other type of cartilage in the knee is called the meniscus. Each knee has two of these smooth, shock-absorbing cartilages which are about a quarter-inch thick. They lie between the thigh bone and shin bone and are usually referred to colloquially as the knee cartilages. These cartilages are attached to the shin bone (or tibia, Y) by long, thin circular ligaments, called coronary ligaments (E and F).

Nicknames for the muscles that control the knee are the quads and hamstrings. The powerful quadriceps muscle of the front thigh is not just one muscle but a group of four muscles working together. Just above the kneecap, they attach onto the patella tendon (A), which then envelops the kneecap, passing over it and attaching below to the shin bone. The lower portion of this tendon is alternatively referred to as the patella ligament (B) or the patella tendon ­ technically it is a ligament functioning as a tendon. (One difficulty with anatomy is that itıs a lot like Russian novels: the same structure, or character, will often have two, three, or even four different names. In this case we will stick with patella tendon.) When the quadriceps muscles of the thigh contract, they pull on the patella tendon and cause the knee to straighten.

Now let's move to the hamstrings, the collective name for the three powerful muscles in the back of the thigh. The tendons of the hamstring muscles cross behind the knee joint and attach on either side of the knee (A and B). This muscle-tendon group bends the knee. I mention the hamstring tendons here because they are often felt as "knee" injuries in the back of the knee.

Another source of potential knee problems if found in the bursas. There are many bursas within the knee, and these fluid-filled sacs offer protection and cushioning. The ones most frequently injured in the knee are the ones beneath the kneecap. In the illustration, the bursa underneath the kneecap is shown as one continuous sac, but in actuality it has three sections that act independently. Each section has its own name, and usually they are injured separately.

© copyright Ben Benjamin 2001