The Knee: An Owner's Manual

Learn how to keep this biomechanical marvel up and running.

By Lisa James

September 2009

Structural Components: The knee’s main structures include:

Bones and Muscles—The tibia, or shinbone, and the smaller fibula meet the femur, or thighbone; the patella, or kneecap, rides over the front of the joint. The large quadriceps muscle in the thigh crosses the knee in the front and controls leg extension. The hamstring, which runs from the hip to the knee in the back, allows the knee to flex, aided by the gastrocnemius, or main calf muscle.

Ligaments and Tendons—Bones are attached to each other by ligaments. The medial collateral (MCL) runs along the inside of the knee and the lateral collateral (LCL) on the outside; the anterior cruciate (ACL) and posterior cruciate (PCL) run through the center. Tendons attach muscles to bones; the kneecap is nestled within the patellar tendon, which attaches the quadriceps to the tibia.

Cartilage—As articular cartilage, this tough, elastic substance lines the bony surfaces within the knee to allow smooth motion. Cartilage also occurs as the lateral meniscus and medial meniscus, two rubber washer-like structures on top of the tibia that provide cushioning and support.

If you live long enough you’re going to develop osteoarthritis—you can put only so many miles on that knee before it breaks down. It doesn’t have to cause pain, though.

—Brian Halpern, MD
Hospital for Special Surgery, New York City; author, The Knee Crisis Handbook (Rodale Books)

Synovial Fluid—A capsule surrounding the knee contains this egg-like substance, generated by the synovial membrane, which allows for easy movement and nourishes the joint’s inner tissues. This fluid is also found in the bursae, small sacs that provide cushioning and reduce friction where tendon meets bone.

Potential Hazards: Arthritis is a catchall term for any condition that causes joint damage, often resulting in pain, inflammation, swelling and, eventually, loss of function; the knee is one of the most common sites. Other hazards include irritation of the bursae (bursitis), tendons (tendinitis) or synovial membrane (synovitis, also known as “water on the knee”), in addition to such injuries as ligament sprains and meniscus tears.

More than 120 disorders fall into the arthritis category; the most prevalent is osteoarthritis (OA), in which the cartilage degrades over time. OA is classified as either secondary, in which it follows a known injury, or primary, in which there is no known cause.

Statistic: 27 million—Americans age 25 and older with OA (Ameri­can College of Rheumatology)

The Experts Say: Only heart disease outpaces arthritis as a cause of work disability.
—Jack E. Jensen, MD, FACSM Athletic Orthopedic and Knee Center, Houston; author, The One Stop Knee Shop (AOK Publishing)


Research continues into the conditions that trigger primary OA. Several risk factors have been identified:

Age—One recent study indicates that levels of a protein known as HMGB2, found in the outermost layers of cartilage, decline with time; another suggests that OA may be a sign of faster “biological aging.”

Statistic: 44.7%—The risk of developing OA symptoms in at least one knee by age 85 (Arthritis Care & Research 9/15/08)

Genetics—More than a dozen genes have been linked to OA.

Misalignment—Being bowlegged, in which the knees splay outwards, or knock kneed, in which they turn inwards, increases risk.

Excess Weight—Puts tremendous stress on the cartilage, leaving it prone to trauma. Excess weight also speeds the rate at which OA progresses.

Diagnostics: A patient with knee pain will be asked about the pain’s nature—when it began, where it hurts, what aggravates it or makes it feel better, etc.—after which the practitioner will gently manipulate the joint to see if there are any alignment or ligament problems. If swelling exists the knee may be aspirated, in which some of the synovial fluid is drawn out with a needle. Imaging studies, including X-rays and MRIs, are used to check the joint’s inner structures; they may show a narrowing of the joint space and/or osteophytes (bone spurs).

The Experts Say: Radiographic findings do not correlate well with symptoms. The person who underwent that X-ray may have no pain, terrible pain or anything in between.
—Grant Cooper, MD Princeton Spine and Joint Center; author, The Arthritis Handbook (DiaMedica Publishing)


The Experts Say: Pain isn’t just nature’s sadism at work. It’s a form of communication—your body is sending up an alert flare.
—Halpern

Preventive Maintenance: Cartilage breakdown is unavoidable over time; the goal is to forestall symptoms, most notably pain. Maintaining a healthy weight—or losing weight if you’re already carrying too many pounds—helps take stress off the knee.

Regular physical activity is crucial for joint health: It helps with weight control, keeps the knee moving freely and strengthens the surrounding muscles. Swimming, bicycling and elliptical training all provide a low-impact workout, as does walking (in properly fitted shoes). Any exercise plan should include stretches, especially those that loosen the quadriceps and hip flexors, which pull the knee upward. Avoid any motion that bends the knee more than 90 degrees, which puts excessive pressure on the cartilage.

The Experts Say: Joints aren’t just capable of motion, they require it. A joint left idle will slowly become less healthy; ultimately it is likely to become painful.
—Cooper

Damage Control: Exercise continues to be important after an arthritis diagnosis; the idea is to avoid a feedback loop in which pain equals less movement and greater disease progression, which in turn equals more pain. A proper diet also helps in healthy weight maintenance. It should include cold-water fish, which supplies anti-inflammatory omega-3 fatty acids (fish oil is another good source). Inflammation-fighting spices can also help. Turmeric, used for centuries in India as an anti-arthritic remedy, contains curcumin, a substance that has shown an ability to ease inflammation in lab studies.

Complementary medicine offers a range of therapies that help ease arthritis symptoms. Yoga, tai chi and acupuncture have been shown in studies to reduce pain and improve quality of life. Prolotherapy, in which sugar water is injected into the joint as a counter-irritant, has helped many people (to find a practitioner, call 800-992-2063 or visit www.aaomed.org).

Supplements that help fight arthritis include:

• Glucosamine/chondroitin—Best-known of the arthritis supplements; together they provide substances that help the body build healthy cartilage and may block the enzyme-related destruction of cartilage. This combination has provided pain relief in several clinical trials.

The Experts Say: ...[T]here is certainly a wealth of anecdotal evidence, including in my own practice, that [glucosamine and chondroitin] work.
—Halpern, Knee Crisis Handbook

• SM—A form of dietary sulphur; it has been found to impede the effects of inflammatory substances on cartilage, particularly in OA’s early stages. Often available in combination with glucosamine and chondroitin.

• Boswellia—An extract taken from Boswellia serrata, or Indian frankincense. Long used in traditional Indian medicine to ease arthritis; possesses anti-inflammatory properties.

• Cat’s claw (una de gato)—An extract from Uncaria tomentosa, an Amazonian rainforest herb; used by traditional healers to ease inflammation and arthritic symptoms.

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