Knee bending pain outside the leg bend may be caused by strenuous exercise, osteophytes, meniscus injury and other conditions. 1. strenuous exercise: after strenuous exercise, may lead to acute injury to the knee cartilage, when the knee bends the leg bend will appear painful symptoms. 2. Meniscus injury: If affected by traumatic factors may lead to meniscus injury, which leads to limited pain, joint swelling, especially the symptoms of pain at the bend of the leg when the knee is bent. 3. Osteomalacia: if the bone degenerative disease, or rheumatoid arthritis, may lead to articular cartilage damage, resulting in bone destruction, serious secondary osteophytes, the symptoms of knee bending leg pain. There are many reasons that lead to pain outside the bend of the knee and leg, you need to go to the hospital as soon as possible to do a checkup and clarify the cause of the disease for treatment.