Anatomy of the knee

The knee joint can be thought of as a hinge joint, with the primary motion of bending and straightening. In reality, it is more complex than a simple hinge, as these surfaces actually glide and roll upon one another. Three bones meet to form the knee joint: the femur (thighbone), the tibia and the patella (kneecap). The bones are covered with smooth cartilage surfaces that act as a cushion during weight-bearing activity.

The bones of the knee are covered with a smooth, glistening layer called articular cartilage and connected by strong ligaments and powerful muscles that are attached to the thigh and calf by tendons, and which provide side-to-side stability. In a healthy knee, all of these structures work together to allow the knee to flex (bend) and extend (straighten) the lower leg smoothly.

The knee can be thought of as having three compartments: the medial (inner), the lateral (outer) and the patellofemoral (where the patella or kneecap meets the femur). In addition, there are two specialized types of cartilage within the knee joint called the lateral and medial meniscus. These act as shock absorbers within the knee joint. Two ligaments – the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) – contribute to the knee's stability.

What is knee arthritis?

Knee arthritis literally means "inflammation of the knee joint," most often as a result of cartilage in the joint wearing down to a degree where it no longer cushions the surfaces of bone which make up the joint. Damaged cartilage causes a roughened joint surface and may lead to bones rubbing directly together. This causes persistent pain, clicking, a catching sensation, and limited range of motion. Healthy articular cartilage can be seen on X-ray as a pronounced spacing between the bones. On an X-ray of a knee with arthritis, this space is reduced or, in some places, even absent due to worn cartilage.

What causes knee arthritis?

There are two basic types of knee arthritis, and they have separate causes. Osteoarthritis, also known as degenerative joint disease is the most common type. This is a slow, progressive in which the articular cartilage of the femur, tibia, or patella wears down over time. It affects most people at some point as they age, usually in their 60s or 70s. Inflammatory arthritis is an autoimmune disorder that may cause inflammation in multiple joints at the same time and may affect young or old people alike.

Osteoarthritis of the knee

In a person with knee osteoarthritis, the normally smooth surfaces of the joint becomes roughened and may cause increased pain, stiffness, and limited motion. Although it is most common in older people, younger patients may get post-traumatic arthritis. This is a form of early onset osteoarthritis that results from an injury to the ligaments, cartilage and/or bone in or around a joint. This causes instability that increases the wearing down of cartilage surfaces.

Inflammatory knee arthritis

Various inflammatory disorders can affect the knee joint, including gout, psoriatic arthritis and rheumatoid arthritis.

What are the symptoms of knee arthritis?

Symptoms include knee joint aching, soreness and pain, and swelling and stiffness. Sometimes this leads to reduced activity and muscle weakness. Weakened muscles can lead to instability and decreased ability to control the knee, further limiting the ability to participate in enjoyable activities. The knee joint may develop cysts, bone spurs, or loss of cartilage. The absence of cartilage will cause friction and narrowing of the joint space.

Symptoms of osteoarthritis of the knee

The loss of the gliding surfaces of the cartilage may make people feel as though their knee is stiff and their motion is limited. Sometimes people actually feel a catching or clicking within the knee. Generally, loading the knee joint with activities such as walking long distances, standing for long periods of time, or climbing stairs makes arthritis pain worse. When the arthritis has gotten to be severe, the pain may occur even when sitting or lying down. The pain is usually felt in the inside part of the knee, but also may be felt in the front or back of the knee. As the cartilage is worn away preferentially on one side of the knee joint, people may find their knee will become more knock-kneed or bowlegged.

Generally, loading the knee joint with activities such as walking long distances, standing for long periods of time, or climbing stairs makes arthritis pain worse. When the arthritis has gotten to be severe, the pain may occur even when sitting or lying down. The pain is usually felt in the inside part of the knee, but also may be felt in the front or back of the knee. As the cartilage is worn away preferentially on one side of the knee joint, people may find their knee will become more knock-kneed or bowlegged.

Symptoms of inflammatory arthritis in the knee

Knee arthritis symptoms can can vary. In rheumatoid arthritis, knee pain usually worsens after periods of rest and inactivity as joints stiffen. Some may experience pain, swelling, redness and warmth, especially in the morning.

What are the risk factors for knee arthritis?

The likelihood of arthritis increases with a family history and advancing age. Patients who are overweight and those who have undergone trauma to the knee joint may also experience early wearing of cartilage.

If I have arthritis in one knee, will I get it in the other?

If you have been diagnosed with osteoarthritis, having an affected knee does not mean that you will develop arthritis in the opposite knee. About 40% of patients who have osteoarthritis in one knee will have the same condition in the other knee. In contrast, patients with rheumatoid arthritis often develop problems in both knees.

What type of doctor treats knee arthritis?

Osteoarthritis of the knee may be treated by a sports medicine physician or an orthopedic surgeon, depending on your particular condition. A physical therapist may be able to treat less severe cases to help reduce pain and increase your mobility. If your knee pain is a result of rheumatoid arthritis, gout or other form of inflammatory arthritis, you should consult a rheumatologist. (Find a doctor who diagnoses and treats knee arthritis.)

How is knee arthritis diagnosed?

An accurate diagnosis for knee arthritis relies on three elements:

• an evaluation and physical exam by a doctor
• X-rays and/or other radiological imaging
• laboratory tests

The physical exam

Your doctor will ask about your medical history and symptoms, and then conduct physical exam to assess:

• your knee pain levels
• range of motion in the knee joint and/or patellofemoral joint
• leg muscle strength
• the presence of any joint swelling or tenderness
• gait (the manner in which you walk)

Radiological examinations

If the physical exam suggests you may have knee osteoarthritis, various types of radiological imaging exams may be used to confirm the diagnosis and determine the level of joint degeneration.

Imaging for diagnosing advanced knee osteoarthritis

X-rays are very helpful in diagnosing advanced knee osteoarthritis because the joint will have specific characteristics, including:

• Bones that are closer to each other than they should be: As cartilage wears away, the joint space between them often narrows.
• Cysts: As the body responds to cartilage destruction and attempts to stabilize the joint, cysts or fluid-filled cavities can form in the bone.
• Increased bone density or uneven joints: When bones are no longer cushioned by cartilage, they can rub against one another, creating friction. The body responds by producing more bone tissue, which increasing bone density. Increased bone creates uneven joint surfaces and bone spurs at the joint.

Is walking good for knee arthritis?

Although it may seem counterintuitive, walking can help decrease the pain and stiffness associated with osteoarthritis. In addition, any form of exercise that helps you maintain a healthy weight can reduce the stress on your joints, and this may slow the progression of your arthritis. You should, however, consult a doctor to confirm that your knee pain is caused by osteoarthritis rather than by an injury for which resting would be appropriate. A physical therapist can help determine appropriate levels of exercise for patients with osteoarthritis of the knee.

Are there any exercises that will help my knee arthritis?

Physical therapy often does help in early stages of arthritis of the knee. An orthopedic doctor or physical therapist can teach you some of these exercises, which focus upon strengthening the quadriceps muscle.

What is the treatment for knee arthritis?

Nonsurgical methods to relieve pain and stiffness should are usually tried first. These may include physical therapy, and/or oral pain medications or injections of corticosteroid or other agents. Inflammatory arthritis in the knee is usually managed medically rather than surgically. For osteoarthritis, and advanced case knee arthritis, knee replacement surgery (whether total or partial) is common, although other surgeries may be appropriate for certain cases.

Nonsurgical treatments for knee arthritis

• Rest and limited activity may be indicated to reduce the symptoms of an inflamed knee joint. You may be advised to refrain from high impact sports, including running, jumping, and any activities in which the impact is repeatedly on the knee joint.
• Weight loss can also reduce stress on the knee joint.
• You may be instructed to participate in low impact activities which will maintain function without overstressing the joint.
• Physical therapy may be recommended to include gentle knee motion exercises such as swimming, water aerobics, walking on a level surface, and using a bicycle to improve range of motion and strengthen the muscles.
• The use of supportive devices (cane, brace orthotics) may also be indicated.
• Nonsteroidal anti-inflammatory medication like aspirin, naproxen, or ibuprofen for pain. Another class of medications called Cox-2 inhibitors such as celecoxib (Celebrex) can reduce inflammation.
• Injections directly into the knee joint may be recommended. These may provide temporary, symptomatic relief, but are not generally recommended or prescribed for prolonged use.

It is difficult to predict the timing and progression of knee arthritis. Sometimes, pain increases and the ability to participate in daily activities decreases despite nonsurgical treatment plans. In those cases, surgery may be recommended.

What is the knee surgery for arthritis?

Although knee replacement for arthritis is the most common and well-known surgery, other procedures may be appropriate for some patients. A knee osteotomy, for example, can help some patients who have a rotational or alignment issue that is accelerating the development of osteoarthritis. Others may benefit from a synovectomy and/or some type of knee arthroscopy.

Surgeries for knee arthritis

Various surgeries may be appropriate, either on their own or in combination with another.

• Total or partial knee replacement surgery. The artificial joint or prosthesis replaces the damaged and worn-out surfaces on the ends of the femur (thighbone) and tibia (shin bone) and the underside of the patella (knee cap) with a new smooth joint surface that will be fixed to the bones. Patellofemoral joint replacement is one form of partial knee replacement.
• Knee arthroscopy to remove spurs or loose bodies, or to aspirate the joint.
• Synovectomy: This is the removal of part of the synovium, the inner lining of the joint capsule. It is a surgical treatment for synovitis − inflammation of the synovium. If a person has effusion (a fluid build-up inside the knee joint capsule, sometimes called “water on the knee”), this may be performed in conjunction with knee arthroscopy to aspirate the joint.
• An osteotomy of the femur and/or tibia – in which bone is cut and realigned – can correctly align the knee to reduce excessive, asymmetrical forces that exacerbate osteoarthritis in one part of the knee. This may be appropriate for people with early onset arthritis caused in part by alignment problems (knock knee, bowleg) or rotational deformities (such as femoral anteversion or femoral retroversion). A person who has a bowleg or knock-knee issue, even if mild, may find their condition becomes more pronounced as knee arthritis advances, since there is greater wearing down of cartilage and bone from one side of the knee as compared to the other.

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