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Common Causes of Knee Pain


As you have seen, the knee is a complex piece of biological machinery made up of bones, cartilage, ligaments, muscles, and tendons. As such, it is very vulnerable to various types of injury; in fact, the knee accounts for 11.2 million visits to physicians’ offices each year and is the anatomical site most often treated by orthopaedic surgeons. Causes of knee pain can be grouped into the following categories:

• Muscle imbalance/relative overuse
• Cartilage injuries and disorders
• Arthritis of the knee
• Ligament injuries
• Tendon injuries and disorders
• Other knee injuries and disorders

Muscle Imbalance/Relative Overuse
Patients with this condition often complain of a vague, deep ache in the front of the knee that is often made worse with running, jumping, climbing stairs, or long periods of rest with the knee bent (for example, at the movies or during air travel). It can affect anyone, but is usually seen in adolescents, athletes, and "weekend warriors."

Cartilage Injuries and Disorders
Meniscal cartilage problems are a common cause of knee pain, affecting millions of Americans annually. One of the most common cartilage problems is a torn meniscus, a condition that often results from sports activities that involve twisting, pivoting, decelerating, cutting, or being tackled. Direct contact is often involved.

Chondrosis (sometimes improperly referred to as Chondromalacia patellae) is characterized by a softening of the articular cartilage in the knee, and may range from mild to severe. There is also a risk that damaged articular cartilage may progress to arthritis—the most frequent cause of long-term knee pain and loss of function.

Arthritis of the Knee
The most common types of arthritis are:

Osteoarthritis (OA)—sometimes called degenerative arthritis because it is a "wearing out" condition involving the breakdown of the cartilage that cushions the knee, much like a tire gradually wears and loses its tread. When the cartilage eventually wears away completely, the bones rub against each other, causing pain and stiffness. OA usually occurs in people over age 50, and is more common when there is a family history of arthritis.
Rheumatoid Arthritis (RA)—a disease that causes the synovium to become thickened and inflamed. In turn, too much abnormal synovial fluid is produced within the joint space, which causes a chronic inflammation that damages the cartilage. This eventually results in cartilage loss, pain, and stiffness.
Post-traumatic Arthritis—can develop after a serious knee injury. Knee fracture or severe laxity of the ligaments from injury may lead to degeneration of the articular cartilage, causing excess wear, pain, and reduced function in the joint over time.

Ligament Injuries
A plague of many athletes and weekend warriors, anterior cruciate ligament injuries—sometimes innocently referred to as a knee "sprain"—are commonly associated with sports activities.

Of the 4 major ligaments found in the knee, the ACL and MCL are the most susceptible to damage, often as a result of changing direction rapidly, twisting, decelerating, or landing from a jump. The PCL can be damaged when the knee is hit front-on or an athlete makes a simple misstep on the playing field, landing with all body forces at the tibial tubercle (bony prominence at the top of the tibia).

Tendon Injuries and Disorders
Knee tendon injuries range from tendinitis (an inflammation of the tendon) to a ruptured (torn) tendon. Inflammation can result from overuse of the tendon, such as during cycling or running, or from repeated strain and impact, such as during basketball. A rupture can occur most commonly when a degenerative tendon (tendonous) undergoes excessive strain as can happen when a person tries to make a cut or break a fall. This often affects the long-term athlete whose tendons may be degenerative because of repetitive "microtrauma."

Osgood-Schlatter disease is a condition characterized by an overuse traction stress reaction of the tibial tubercle growth plate pulled upon by the patellar tendon. Usually caused by repetitive stress, the condition most often occurs in the teenage athlete who is still growing; in some cases, the growth plate may be injured so much that it tears away from the tibia and takes a fragment of bone and growth plate.

Another overuse condition is Iliotibial Band Syndrome. The iliotibial band is a strip of connective tissue that inserts into the upper part of the tibia after a long course from the pelvis. As the knee bends and extends, this band repeatedly rubs over the outer bone of the knee, which can cause the tendon and intervening structures to become inflamed.

Other Knee Injuries and Disorders
Knee pain can also result from other conditions that do not fit neatly into any of the above categories.

Osteochondritis Dissecans results from a loss of the blood supply to an area of bone underneath a joint surface, such as the knee. The loss of blood supply—which may be caused by a slight blockage of a small artery, or repetitive microtrauma stress fracture—causes the bone to die; eventually, the injured cartilage and bone may separate from the deeper, healthy bone. This fragment may break loose into the knee joint.

Plica syndrome occurs when plicae (bands of remnant synovial tissue) are irritated by overuse or injury. The condition can develop over a long period of time due to repetitive motion, such as biking or use of a stair stepper, or can happen suddenly when the knee is struck in an area that impacts the plicae.


Bursitis refers to a condition affecting the bursa, a small fluid-filled sac that cushions the points of contact between bones, tendons, and ligaments. When the bursa just in front of the kneecap becomes inflamed, it causes swelling and tenderness in front of the knee. This condition, known as prepatellar bursitis, often affects people whose work requires a great deal of bending and kneeling (repetitive microtrauma to the bursa), such as plumbers, roofers, carpet layers, and gardeners; it can also be caused by injury or rheumatoid arthritis.
Osteoarthritis and Rheunatoid arthritis


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