Call for emergency medical help. If you suspect you're having a heart attack, don't hesitate. Immediately call 911 or your local emergency number. If you don't have access to emergency medical services, have someone drive you to the nearest hospital.
The most common causes of knee weakness are osteoarthritis, sprain or strain, and chronic knee pain. Other possible causes, such as injury to the knee, are more rare. Osteoarthritis 22. Sprain or strain 17. Chronic knee pain 15. Knee ligament or meniscus tear 8. Fracture of the leg 4. Bursitis 2.
Some of the most common reasons for knee pain are sprained ligaments, meniscus (cartilage) tears, tendonitis, and runner's knee. But the knee is a complex joint, and there's plenty more that can go wrong. In this condition, the kneecap slides out of position, causing knee pain and swelling. 2  Patellofemoral pain syndrome. 3  This condition often results from issues associated with muscle imbalance, tightness, and alignment of the legs, rather than an injury.