Where two or more bones meet is called a joint. There
are different types of joint all through your body. Some joints are
fixed, which means they cannot move at all. Other joints allow movement –
different joints in different ways. ‘Ball and socket’ joints, like your
hip or shoulder, allow the biggest range of movement. ‘Hinge’ joints,
like your knee or elbow, allow movement up and down. ‘Pivot’ joints,
like your neck, allow you to rotate your head from side to side.
This word means 'child' so a disease that affects children is a 'juvenile' disease – like juvenile arthritis.