The knee is a joint that takes a lot of abuse. It carries around much of the weight from the body during the day while walking, and even sitting. When you lie down at night, the knees are sometimes bent a good portion of the night, causing even more strain on the knees. There are many causes as to why your knees will hurt, and when they do, you need to see a doctor. The most common reason people have knees that hurt is due to old age. Older people, as well as some younger people, get Arthritis in their joints. This includes the knee joint. Arthritis sets up in the knee, and is often more prevalent when the weather is damp or cold. When the knee starts to ache, apply a heated medication on the knee to ease the muscles. Injuries are the next thing that causes knee pain. The way the knee is injured will affect how the knee is treated as well as how long it takes for the knee to heal. Sports injuries are common with younger people. Children do not get hurt in their knees as much as middle age children. Basketball and soccer are probably two of the leading sports that players get hurt in. the knee turns easily while running and jumping, and these activities are common in both sports. People who play basketball face more challenges with the knees because of the fast pace of the game and the turning of the knee throughout the entire game. When the knee is injured while playing a sport, it is usually quick and intense. The cartilage is usually torn in the knee as the knee turns. Falling is another cause for knee pain. Older people are more prone to falling and need to be monitored. If they fall forward, they will sometimes land on their hands, elbows, and more likely their knees. Falls can damage the fronts of the kneecaps. Damage to the knees in older individuals sometimes will require surgery in order to replace the cap of the knee or the joint itself. Some diseases will also affect the knee and cause pain, such as bone cancer.