The knees are vulnerable to injury. From walking to running, the knee joints take a lot of strain. The most common causes of short-lived or chronic knee pain are: Anterior Cruciate Ligament (ACL) tear – common in athletes or people who play sports Meniscus cartilage tear – often happens if you twist the knee suddenly while you’re putting weight on it Tissue inflammation Patellar tendinitis – irritation of a tendon around the knee joint Minor joint fractures Dislocation Iliotibial band syndrome – common in cyclists and distance runners Less common causes of knee pain include: Gout Infection around the knee joint Osteoarthritis Rheumatoid arthritis Obesity, which places chronic extra stress on the joints A loose body, which is when a bone or cartilage fragment breaks away and causes discomfort in the joint space