This is one of the commonest sporting injuries, often caused by someone attempting to kick a ball and kicking the ground instead. It may also occur in accidents in which the knee is twisted sideways while slightly flexed. The result is that one of the two ‘floating’ cartilages in the knee joint tear, usually at the inside of the knee. The casualty will be in extreme pain, and unable to straighten the leg. The knee joint may be swollen. Do not try to straighten the knee, which should instead be supported and made comfortable with cushions or other padding. If medical help is not immediately available, and if it is necessary to move the casualty, the injured leg should be crossed over the uninjured leg at the calf, and the two tied together with bandages. Such an injury may necessitate an operation to remove the damaged cartilage to stop the problem recurring.