By Nathan Wei
When your knee hurts, getting relief is all that’s on your mind. Getting the right relief, though, depends on knowing what’s wrong. The correct diagnosis will lead to the correct treatment.
Know Your Knee!
The knee is the largest joint in the body. It’s also one of the most complicated. The knee joint is made up of four bones that are connected by muscles, ligaments, and tendons. The femur (large thigh bone) interacts with the two shin bones, the tibia (the larger one) located towards the inside and the fibula (the smaller one) located towards the outside. Where the femur meets the tibia is termed the joint line. The patella, (the knee cap) is the bone that sits in the front of the knee. It slides up and down in a groove in the lower part of the femur (the femoral groove) as the knee bends and straightens.
Ligaments are the strong rope-like structures that help connect bones and provide stability. In the knee, there are four major ligaments. On the inner (medial) aspect of the knee is the medial collateral ligament (MCL) and on the outer (lateral) aspect of the knee is the lateral collateral ligament (LCL). The other two main ligaments are found in the center of the knee. These ligaments are called the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). They are called cruciate ligaments because the ACL crosses in front of the PCL. Other smaller ligaments help hold the patella in place in the center of the femoral groove.
Two structures called menisci sit between the femur and the tibia. These structures act as cushions or shock absorbers. They also help provide stability for the knee. The menisci are made of a tough material called fibrocartilage. There is a medial meniscus and a lateral meniscus. When either meniscus is damaged it is called a “torn cartilage”.
There is another type of cartilage in the knee called hyaline cartilage. This cartilage is a smooth shiny material that covers the bones in the knee joint. In the knee, hyaline cartilage covers the ends of the femur, the femoral groove, the top of the tibia and the underside of the patella. Hyaline cartilage allows the knee bones to move easily as the knee bends and straightens.
Tendons connect muscles to bone. The large quadriceps muscles on the front of the thigh attach to the top of the patella via the quadriceps tendon. This tendon inserts on the patella and then continues down to form the rope-like patellar tendon. The patellar tendon in turn, attaches to the front of the tibia. The hamstring muscles on the back of the thigh attach to the tibia at the back of the knee. The quadriceps muscles are the muscles that straighten the knee. The hamstring muscles are the main muscles that bend the knee.
Bursae are small fluid filled sacs that decrease the friction between two tissues. Bursae also protect bony structures. There are many different bursae around the knee but the ones that are most important are the prepatellar bursa in front of the knee cap, the infrapatellar bursa just below the kneecap, the anserine bursa, just below the joint line and to the inner side of the tibia, and the semimembranous bursa in the back of the knee. Normally, a bursa has very little fluid in it but if it becomes irritated it can fill with fluid and become very large.
Is it bursitis… or tendonitis…or arthritis?
Tendonitis generally affects either the quadriceps tendon or patellar tendon. Repetitive jumping or trauma may set off tendonitis. The pain is felt in the front of the knee and there is tenderness as well as swelling involving the tendon. With patellar tendonitis, the infrapatellar bursa will often be inflamed also. Treatment involves rest, ice, and anti-inflammatory medication. Injections are rarely used. Physical therapy with ultrasound and iontopheresis may help.
Bursitis pain is common. The prepatellar bursa may become inflamed particularly in patients who spend a lot of time on their knees (carpet layers). The bursa will become swollen. The major concern here is to make sure the bursa is not infected. The bursa should be aspirated (fluid withdrawn by needle) by a specialist. The fluid should be cultured. If there is no infection, the bursitis may be treated with anti-jnflammatory medicines, ice, and physical therapy. Knee pads should be worn to prevent a recurrence once the initial bursitis is cleared up.
Anserine bursitis often occurs in overweight people who also have osteoarthritis of the knee. Pain and some swelling is noted in the anserine bursa. Treatment consists of steroid injection, ice, physical therapy, and weight loss.
The semimembranous bursa can be affected when a patient has fluid in the knee (a knee effusion). The fluid will push backwards and the bursa will become filled with fluid and cause a sensation of fullness and tightness in the back of the knee. This is called a Baker’s cyst. If the bursa ruptures, the fluid will dissect down into the calf. The danger here is that it may look like a blood clot in the calf. A venogram and ultrasound test will help differentiate a ruptured Baker’s cyst from a blood clot. The Baker’s cyst is treated with aspiration of the fluid from the knee along with steroid injection, ice, and elevation of the leg.
Knock out knee arthritis… simple steps you can take! Younger people who have pain in the front of the knee have what is called patellofemoral syndrome (PFS). Two major conditions cause PFS. The first is chondromalacia patella. This is a condition where the cartilage on the underside of the knee cap softens and is particularly common in young women. Another cause of pain behind the knee cap in younger people may be a patella that doesn’t track normally in the femoral groove. For both chondromalacia as well as a poorly tracking patella, special exercises, taping, and anti-inflammatory medicines may be helpful. If the patellar tracking becomes a significant problem despite conservative measures, surgery is need.
While many types of arthritis may affect the knee, osteoarthritis is the most common. Osteoarthritis usually affects the joint between the femur and tibia in the medial (inner) compartment of the knee. Osteoarthritis may also involve the joint between the femur and tibia on the outer side of the knee as well as the joint between the femur and patella. Why osteoarthritis develops is still being scrutinized carefully. It seems to consist of a complex interaction of genetics, mechanical factors, and immune system involvement. The immune system attacks the joint through a combination of degradative enzymes and inflammatory chemical messengers called cytokines.
Patients will sometimes feel a sensation of rubbing or grinding. The knee will become stiff if the patient sits for any length of time. With local inflammation, the patient may experience pain at night and get relief from sleeping with a pillow between the knees. Occasionally, locking and clicking may be noticed. Patients with osteoarthritis may also tear the fibrocartilage cushions (menisci) in the knee more easily than people without osteoarthritis.
So how is the arthritis treated? An obvious place to start is weight reduction for patients who carry around too many pounds.
Strengthening exercises for the knee are also useful for many people. These should be done under the supervision of a physician or physical therapist.
Other therapies include ice, anti inflammatory medicines, and occasionally steroid injections. Glucosamine and chondroitin supplements may be helpful. A word of caution… make sure the preparation you buy is pure and contains what the label says it does. The supplement industry is unregulated… so buyer beware!
Injections of the knee with viscosupplements – lubricants- are particularly useful for many patients. Special braces may help to unload the part of the joint that is affected.
Arthroscopic techniques may be beneficial in special circumstances. Occasionally, a surgical procedure called an osteotomy, where a wedge of bone is removed from the tibia to “even things out,” may be recommended. Joint replacement surgery is required for end stage knee arthritis.
Research is being done to develop medicines that will slow down the rate of cartilage loss. Targets for these new therapies include the destructive enzymes and/or cytokines that degrade cartilage. It is hoped that by inhibiting these enzymes and cytokines and by boosting the ability of cartilage to repair itself, that therapies designed to actually reverse osteoarthritis may be created. These are referred to as disease-modifying osteoarthritis drugs or “DMOADs.” Genetic markers may identify high risk patients who need more aggressive therapies.
Newer compounds that are injected into the knee and provide healing as well as lubrication are also being developed. And finally, less invasive surgical techniques are also being looked at. Recent technological advances in “mini” knee replacement look very promising.
Dr. Wei (pronounced “way”) is a board-certified rheumatologist and Clinical Director of the nationally respected Arthritis and Osteoporosis Center of Maryland. He is a Clinical Assistant Professor of Medicine at the University of Maryland School of Medicine and has served as a consultant to the Arthritis Branch of the National Institutes of Health. He is a Fellow of the American College of Rheumatology and the American College of Physicians.