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The New Joint

Prone to wear, tear and disease, knees usually can’t be healed, but they can be replaced

by Ann Morrow on August 14, 2014


“Your leg bone connected to your knee bone, your knee bone connected to your thigh bone . . .”

Actually, the elements that comprise the human knee are considerably more intricate than the children’s song describes: The lower end of the femur (thigh bone) is connected to the patella (kneecap) which is connected to the upper end of the tibia (shinbone), and all of it is covered with articular cartilage, a smooth substance the prevents the bones from rubbing against each other, and contains menisci (wedges) that act as shock absorbers—in total, creating the largest joint in the body.

This marvel of anatomical engineering enables us to walk, run, jump, pivot, squat, and swing the lower leg back and forth while slightly rotating from side to side. A healthy knee allows for 150 degrees of movement, and is required to perform almost all the activities of daily life. But because of its complexity, much can go wrong.

One prevalent problem is that articular cartilage wears out from use, and has little to no ability to repair or regenerate itself. Knee bone is also vulnerable to three kinds arthritis: osteoarthritis, a progressive condition associated with wear and aging; rheumatoid arthritis, an inflammatory disease; and post-traumatic arthritis, which can set in years after an injury.

There are also three common lifestyle problems that can cause degeneration of the knee: obesity, which puts a disproportionate amount of stress on the joint (even as little as an extra 10 pounds can have an effect); lack of exercise, which deteriorates the muscles needed for joint support as well as diminishing flexibility and reducing blood circulation; and poor posture, since being out of alignment, especially during physical activity such as running or weightlifting, but also for standing and sitting, puts stress on all the joints and causes extra wear on knee cartilage.

Indications of knee damage include pain and stiffness, swelling, and sometimes a grinding sensation from the within the knee caused by the bones rubbing together from a lack of cushioning and lubrication.

Fortunately, the knee can be replaced. Knee replacement surgery, in which the kneecap and articular cartilage are replaced with a mechanical implant, is one the most common surgeries, and has among the highest success rates and lowest incidence of serious complications. It rates very highly for patient satisfaction: According to the American Academy of Orthopedic Surgeons, 90 percent of patients undergoing TKR (total knee replacement) experience a dramatic reduction in pain and significant improvement in the ability to perform daily activities (and more specifically, in the maximum flexion of the knee).

In TKR, an incision is made above the knee, usually between 4 and 10 inches long, and damaged bone and cartilage is cut away and replaced with biocompatible plastic and metal. Two methods are used to seal the components: bone cement, or a porous coating that grows into tissue or attaches to bone. Sometimes both methods are used. The surgery takes approximately an hour and half. TKR tends to be long-lasting, too—devices lasting 20 years or more are not uncommon, which also accounts for the surgery’s popularity.

There is a major caveat, however. Physical therapy is key, both before and after. The course of therapy can be extensive, yet dropping out too soon can significantly diminish the effectiveness of the surgery. And running is often not recommended, regardless of the patient’s age, due to the impact on the device. However, walking is highly encouraged, one of the reasons being that cartilage is like a sponge, and the compression and decompression of body weight (which the knee helps to distribute) brings nutrients that bone and cartilage need to stay strong and supple.

As Denver physical therapist Eric Robertson said in a WebMD forum:

“Trust your body and trust the fact that we are made to move, and motion itself has a healing effect. What may feel a little achy at first will have some great results.”