The knee is a hinge joint between the upper and lower leg bones. Two cartilage cushions, the medial and lateral meniscus, minimize friction between the leg bones at the knee. The kneecap, or patella, shields the joint. The inner aspect of the patella is also lined with cartilage, which facilitates smooth movement of the leg bones behind the kneecap. Problems with the meniscal or patellar knee cartilage typically cause pain and can significantly interfere with normal knee function.
Knee Arthritis
Osteoarthritis, rheumatoid and post-traumatic arthritis can progressively destroy the knee cartilage. With osteoarthritis, the knee cartilage slowly deteriorates due to progressive wear. In a 2008 research study published by "Arthritis Care & Research," Louise Murphy, Ph.D., and colleagues report that the lifetime risk for symptomatic osteoarthritis of the knee approaches nearly 50 percent. The level of risk increases with obesity, advancing age and a history of prior knee injury. According to the American Academy of Orthopaedic Surgeons, in 2005, an estimated 9 million Americans were living with osteoarthritis of the knee.
Rheumatoid arthritis is an autoimmune disorder of the joints. Cartilage is destroyed by enzymes released during ongoing immune system activity within the joint, explains the National Institute of Arthritis and Musculoskeletal and Skin Diseases. Approximately 20 to 30 percent of patients with rheumatoid arthritis have knee involvement, according to the University of Washington Department of Orthopaedics and Sports Medicine.
Meniscus Tears
Traumatic injury or degenerative changes in the knee menisci can lead to tears. The American Academy of Orthopaedic Surgeons explains that different types of meniscus tears occur, some more serious than others. Full-thickness tears, or grade IV lesions, represent the most severe meniscus injuries. With a grade IV meniscus tear, a piece of torn cartilage may break free and float within the knee joint, obstructing complete straightening and bending of the knee.
Less severe meniscus tears typically do not limit the ability to walk, but may cause problems with certain types of activities, especially those that involve twisting or fully bending the knee, notes the University of Washington Department of Orthopaedics and Sports Medicine.
Chondromalacia Patella
Chondromalacia patella is a degenerative ailment of the patellar cartilage caused by knee overuse or misalignment of the kneecap over the leg bones. The patient information website eOrthopod reports that chondromalacia patella most commonly develops in people who participate in sports or recreational activities that repetitively stress the knee including running, cycling, soccer, rowing, and snowboarding or skiing. This condition typically causes localized pain with prolonged or repetitive knee bending. Swelling and a grinding sensation often accompany knee pain.
References
- "Arthritis Care & Research"; Lifetime Risk of Symptomatic Knee Osteoarthritis; Louise Murphy, Ph.D., et al.; September 2008
- American Academy of Orthopaedic Surgeons: Knee Osteoarthritis Statistics
- National Institute of Arthritis and Musculoskeletal and Skin Diseases: Handout on Health, Rheumatoid Arthritis
- UW Medicine Orthopaedics and Sports Medicine: Knee Surgery for Rheumatoid Arthritis
- American Academy of Orthopaedic Surgeons: Meniscal Tears
