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Causes

By Mayo Clinic staff

CLICK TO ENLARGE

Illustration showing anterior cruciate ligament Anterior cruciate ligament
Image showing knee anatomy and torn meniscus Torn meniscus
Illustration showing area of pain in Osgood-Schlatter disease Osgood-Schlatter disease

Knee pain can be caused by injuries, mechanical problems, types of arthritis and other problems.

Injuries
A knee injury can affect any of the ligaments, tendons or fluid-filled sacs (bursae) that surround your knee joint as well as the bones, cartilage and ligaments that form the joint itself. Some of the more common knee injuries include:

  • ACL injury. An ACL injury is the tearing of the anterior cruciate ligament (ACL) — one of four ligaments that connect your shinbone to your thighbone. An ACL injury is particularly common in people who play basketball or go downhill skiing, because it's linked to sudden changes in direction.
  • Torn meniscus. The meniscus is formed of tough, rubbery cartilage and acts as a shock absorber between your shinbone and thighbone. It can be torn if you suddenly twist your knee while bearing weight on it.
  • Knee bursitis. Some knee injuries cause inflammation in the bursae, the small sacs of fluid that cushion the outside of your knee joint so that tendons and ligaments glide smoothly over the joint.
  • Patellar tendinitis. Tendinitis is irritation and inflammation of one or more tendons — the thick, fibrous cords that attach muscles to bones. Runners, skiers and cyclists are prone to develop inflammation in the patellar tendon, which connects the quadriceps muscle on the front of the thigh to the shinbone.

Mechanical problems

  • Loose body. Sometimes injury or degeneration of bone or cartilage can cause a piece of bone or cartilage to break off and float in the joint space. This may not create any problems unless the loose body interferes with knee joint movement — the effect is something like a pencil caught in a door hinge.
  • Knee 'locking.' This can occur from a cartilage tear. When a portion of cartilage from the tear flips inside the knee joint, you may not be able to fully straighten your knee.
  • Dislocated kneecap. This occurs when the triangular bone (patella) that covers the front of your knee slips out of place, usually to the outside of your knee. You'll be able to see the dislocation, and your kneecap is likely to move excessively from side to side.
  • Hip or foot pain. If you have hip or foot pain, you may change the way you walk to spare these painful joints. But this altered gait can interfere with the alignment of your kneecap and place more stress on your knee joint. In some cases, problems in the hip or foot can refer pain to the knee.

Types of arthritis

  • Osteoarthritis. Sometimes called degenerative arthritis, osteoarthritis is the most common type of arthritis. It's a wear-and-tear condition that occurs when the cartilage in your knee deteriorates with use and age.
  • Rheumatoid arthritis. The most debilitating form of arthritis, rheumatoid arthritis is an autoimmune condition that can affect almost any joint in your body, including your knees. Although rheumatoid arthritis is a chronic disease, it tends to vary in severity and may even come and go.
  • Gout. This type of arthritis occurs when uric acid crystals build up in the joint. While gout most commonly affects the big toe, it can also occur in the knee.
  • Pseudogout. Often mistaken for gout, pseudogout is caused by calcium pyrophosphate crystals that develop in the joint fluid. Knees are the most common joint affected by pseudogout.
  • Septic arthritis. Sometimes your knee joint can become infected, leading to swelling, pain and redness. There's usually no trauma before the onset of pain. Septic arthritis often occurs with a fever.

Other problems

  • Iliotibial band syndrome. This occurs when the ligament that extends from the outside of your pelvic bone to the outside of your tibia (iliotibial band) becomes so tight that it rubs against the outer portion of your femur. Distance runners are especially susceptible to iliotibial band syndrome.
  • Chondromalacia patellae (patellofemoral pain syndrome). This is a general term that refers to pain arising between your patella and the underlying thighbone (femur). It's common in young adults, especially those who have a slight misalignment of the kneecap; in athletes; and in older adults, who usually develop the condition as a result of arthritis of the kneecap.
  • Osgood-Schlatter disease. This condition affects the softer area of bone near the top of the shinbone, where bone growth occurs. It's most common in boys who play games or sports that involve running or jumping. The discomfort can last a few months and may continue to recur until the child's bones stop growing.
  • Osteochondritis dissecans. Caused by reduced blood flow to the end of a bone, osteochondritis dissecans is a joint condition in which a piece of cartilage, along with a thin layer of the bone beneath it, comes loose from the end of a bone. It occurs most often in young men, particularly after an injury to the knee.
Risk factors Symptoms
References
  1. Questions and answers about knee problems. National Institute of Arthritis and Musculoskeletal and Skin Diseases. http://www.niams.nih.gov/Health_Info/Knee_Problems/default.asp. Accessed July 23, 2010.
  2. Huddleston JI, et al. Hip and knee pain. In: Firestein GS, et al. Kelley's Textbook of Rheumatology. 8th ed. Philadelphia, Pa.: W.B. Saunders Co.; 2008. http://www.mdconsult.com/das/book/body/211216621-3/1029261530/1807/290.html#4-u1.0-B978-1-4160-3285-4..10042-7--s0010_1200. Accessed July 23, 2010.
  3. Anderson RJ, et al. Evaluation of the adult patient with knee pain. http://www.uptodate.com/home/index.html. Accessed July 23, 2010.
  4. Common knee injuries. American Academy of Orthopaedic Surgeons. http://www.orthoinfo.org/topic.cfm?topic=A00325. Accessed July 23, 2010.
  5. Zeller JL, et al. JAMA patient page: Knee pain. Journal of the American Medical Association. 2007;297:1740.
  6. Pallin DJ, et al. Knee injuries. In: Marx JA, et al. Rosen's Emergency Medicine. 7th ed. Philadelphia, Pa.: Mosby Elsevier; 2009. http://www.mdconsult.com/book/player/book.do?method=display&type=bookPage&decorator=header&eid=4-u1.0-B978-0-323-05472-0..00054-2--s0150&displayedEid=4-u1.0-B978-0-323-05472-0..00054-2--s0460&uniq=211216621&isbn=978-0-323-05472-0&sid=1029279549. Accessed July 23, 2010.
  7. Pseudogout. American College of Rheumatology. http://www.rheumatology.org/public/factsheets/diseases_and_conditions/pseudogout. Accessed July 23, 2010.
  8. Pallin DJ, et al. Diagnostic strategies. In: Marx JA, et al. Rosen's Emergency Medicine. 7th ed. Philadelphia, Pa.: Mosby Elsevier; 2009. http://www.mdconsult.com/book/player/book.do?method=display&type=bookPage&decorator=header&eid=4-u1.0-B978-0-323-05472-0..00054-2--s0150&displayedEid=4-u1.0-B978-0-323-05472-0..00054-2--s0470&uniq=211216621&isbn=978-0-323-05472-0&sid=1029395050#lpState=open&lpTab=contentsTab&content=4-u1.0-B978-0-323-05472-0..00054-2--s0100%3Bfrom%3Dtoc%3Btype%3DbookPage%3Bisbn%3D978-0-323-05472-0. Accessed July 23, 2010.
  9. Care of the aging or post-traumatic knee. American Academy of Orthopaedic Surgeons. http://orthoinfo.aaos.org/topic.cfm?topic=A00344. Accessed July 23, 2010.
  10. Knee bracing: What works? American Academy of Family Physicians. http://familydoctor.org/online/famdocen/home/healthy/physical/injuries/490.html. Accessed July 23, 2010.
  11. Roberts WN. Intraarticular and soft tissue injections: What agents to inject and how frequently? http://www.uptodate.com/home/index.html. Accessed July 23, 2010.
  12. LeBlanc KE, et al. Musculoskeletal disorders. Primary Care Clinical Office Practice. 2010;37:389.
  13. Knee implants. American Academy of Orthopaedic Surgeons. http://orthoinfo.aaos.org/topic.cfm?topic=A00221. Accessed July 23, 2010.
  14. Anderson BC. Patient information: Knee pain. http://www.uptodate.com/home/index.html. Accessed July 26, 2010.
  15. Acupuncture for pain. National Center for Complementary and Alternative Medicine. http://nccam.nih.gov/health/acupuncture/acupuncture-for-pain.htm. Accessed July 26, 2010.
  16. Laskowski ER (expert opinion). Mayo Clinic, Rochester, Minn. July 26, 2010.
DS00555 Sept. 9, 2010

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