Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Knee Injuries and Disorders ?
    ### Response:
    Your knee joint is made up of bone, cartilage, ligaments and fluid. Muscles and tendons help the knee joint move. When any of these structures is hurt or diseased, you have knee problems. Knee problems can cause pain and difficulty walking.    Knee problems are very common, and they occur in people of all ages.
    