Basically, the knee is two long leg bones held together by muscles, ligaments, and tendons. There are two groups of muscles involved in the knee. The quadriceps muscles, which are located on the front of the thigh, straighten the leg. The hamstring muscles, which are located on the back of the thigh, bend the leg at the knee. Tendons are tough cords of tissue that connect muscles to bones.
Ligaments are elastic bands of tissue that connect bone to bone.
Some ligaments on the knee provide stability and protection of the joints, while other ligaments limit forward and backward movement of the tibia. Other knee problems are a result of an injury or a sudden movement that strains the knee. Symptoms often include pain, swelling, and difficulty in walking. Cartilage tears can often occur with sprains. Treatment may involve wearing a brace during an activity to protect the knee form further injury.