Arthritis Joint Pain Print What Is Causing Your Knee Pain? Medically reviewed by Medically reviewed by Grant Hughes, MD on August 05, 2016 Grant Hughes, MD is board-certified in rheumatology and is the head of rheumatology at Seattle's Harborview Medical Center. Learn about our Medical Review Board Grant Hughes, MD Written by facebook Written by Carol Eustice Carol Eustice is a writer who covers arthritis and chronic illness. She is the author of "The Everything Health Guide to Arthritis." Learn about our editorial policy Carol Eustice Updated on November 16, 2019 More in Arthritis Joint Pain Causes & Risk Factors Living With Support & Coping Rheumatoid Arthritis Gout Ankylosing Spondylitis Diagnosis Symptoms Treatment Osteoarthritis More Arthritis Types & Related Conditions Psoriatic Arthritis View All To understand the causes of knee pain, it helps to learn about the structures of the knee and common conditions that can affect them. 1 Normal Knee Joint The structure of a normal knee joint. Stocktrek Images/Getty Images The knee is a hinge joint formed by two bones, the femur and tibia, which are held together by four ligaments—the medial collateral ligament, lateral collateral ligament, anterior cruciate ligament, and posterior cruciate ligament. The patella (knee cap) is also part of normal knee anatomy. The ends of the femur and tibia, as well as the underside of the patella, are covered by articular cartilage, a slippery surface that allows friction-free, pain-free movement. 2 Synovial Fluid in a Normal Knee Joint CLAUS LUNAU / Getty Images A normal knee joint is surrounded by a membrane, the synovium, which produces a small amount of thick fluid, known as synovial fluid. Synovial fluid helps to nourish the cartilage and keep it slippery. The synovium also has a tough outer layer (the joint capsule) which protects and supports the joint. 3 Inflamed Synovium in Rheumatoid Arthritis In rheumatoid arthritis, an autoimmune disease, the body attacks its own joints. White blood cells, which are agents of the immune system, travel to the synovium and cause an inflammatory process to occur, referred to as active synovitis. The inflamed synovium causes warmth, redness, swelling, and pain in and around the affected joint. Specifically, during the inflammatory process, the synovium thickens and causes the joint to swell. As rheumatoid arthritis progresses, abnormal synovial cells invade and erode cartilage and bone within the joint. Surrounding muscles, ligaments, and tendons weaken. Basic Facts About Rheumatoid Arthritis 4 Joint Damage in Osteoarthritis of Knee BSIP/UIG / Getty Images In osteoarthritis, commonly called wear-and-tear arthritis, the surface layer of cartilage breaks down and wears away. With advanced disease, the breakdown of cartilage can become so severe that the bones of the joint rub together (referred to as bone-on-bone). Pain, swelling, and limited range of motion result. The joint may lose its normal shape over time and become deformed, too. Bone spurs (osteophytes) can develop along the edges of the joint. Bits of bone or cartilage can break off and float inside the joint space, causing even more pain and damage (i.e., loose bodies). Everything You Need to Know About Knee Osteoarthritis 5 Specific Location of Knee Pain Hero Images / Getty Images The location of the knee pain can be useful information when trying to obtain an accurate diagnosis. Pain at the front of the knee can be caused by bursitis, arthritis, or softening of the patella cartilage, as in chrondromalacia patella. Pain on the side of the knee is usually associated with injury to the collateral ligaments, arthritis, or tears to the menisci. Pain in the back of the knee can be caused by arthritis or a Baker's cyst (an accumulation of synovial fluid behind the knee). Infection may be another possible cause of knee pain. While the location of knee pain offers significant clues as to the cause, imaging studies (X-ray, CT scan, or MRI) provide visible evidence of damage and abnormalities. Appropriate treatment clearly depends on an accurate diagnosis of what's causing your knee pain. Was this page helpful? Thanks for your feedback! Dealing with chronic inflammation? An anti-inflammatory diet can help. Our free recipe guide shows you the best foods to fight inflammation. Get yours today! Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Andrews K, Lu A, Mckean L, Ebraheim N. Review: Medial collateral ligament injuries. J Orthop. 2017;14(4):550-554. Raines BT, Naclerio E, Sherman SL. Management of Anterior Cruciate Ligament Injury: What's In and What's Out?. Indian J Orthop. 2017;51(5):563–575. doi:10.4103/ortho.IJOrtho_245_17 Logterman SL, Wydra FB, Frank RM. Posterior Cruciate Ligament: Anatomy and Biomechanics. 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