Medically Reviewed by Eric Heimberger, MD

First, a few facts. Feel free to use these at your next cookout or family dinner.

The knee is the largest joint in the body. With good reason. Walking and running. Turning, crouching, climbing stairs and jumping. Or, simply standing around. In nearly every activity we undertake, the knee plays a key role.

“Americans are living longer, more active lives; so, it’s no surprise that problem knee joints are a growing problem, leading to total knee joint replacement,” says McLeod Orthopedic Surgeon Dr. Eric Heimberger of McLeod Orthopaedics Seacoast. “The three main triggers leading to a degeneration of the knee are simple wear & tear, arthritis and injury.”

1. Wear & Tear

Cartilage is the substance that covers the joints and essentially lubricates movement. In the knee, cartilage covers the ends of bones and the underside of the kneecap. All cartilage wears with use, leading to many knee joint replacements in people over 65 years of age.

Younger – but maturing people in their 40s and 50s who play a lot of sports – can feel the problem sooner.

Some jobs that require extensive kneeling, crouching or climbing can endanger the cartilage. For instance, house painters that climb ladders and kneel to paint low spots are especially susceptible to this wear.

2. Arthritis

Arthritis of the knee is the leading cause of disability in the US. There are basically 2 types of this disease that can cause knees to degenerate.

• Osteoarthritis – informally known as “wear & tear” arthritis – can be triggered when cartilage is worn down or irritated. This is commonly found in people age 50 or older. Obesity is another risk factor.

• Rheumatoid Arthritis (RA) inflames and destroys the cartilage. In that respect, it can affect many joints in the body, generally affects both knees, and can occur at any age. Sufferers say it feels like a burning, often accompanied by swelling. Speaking of burning, smoking is a risk factor in causing RA.

3. Injury

An injury or impact to the knee can cause physical damage. Injuries could be as mild as a sprain – caused by sudden or unnatural twisting – or as severe as a kneecap fracture – usually caused by hitting something very hard. In some cases, the damage will trigger arthritis.

Symptoms of Knee Degeneration

Common symptoms include stiff joints or pain. If the cartilage is heavily worn, a person may also feel the “grating” of bone-on-bone or a “catch” when they move the knee. At its worst, it is disabling.

When To See A Doctor

A range of treatments can return you to normal activity. Minor pain can be handled with over-the-counter medication, such as ibuprofen. But don’t ignore pain that continues.

Here are some guidelines on when to see a doctor, if:

• Knee pain lasts 3 or more days
• You feel the pain at night or when sitting down
• It’s difficult to put weight on your knee and may buckle when you move
• It clicks or locks up

To find a physician, click here.

Sources include: McLeod Health, American Academy of Orthopaedic Surgeons, National Institutes of Health, UCSF, Arthritis Foundation, National Health System (UK), Rheumatology Reports