England captain Michael Vaughan will undergo yet another knee operation, forcing him to miss England's defence of the Ashes in Australia.
Vaughan has suffered knee cartilage problems at different points during his career and has been treated by surgeon Derek Bickerstaff.
Here, Dr Bickerstaff, who has operated on many of England's top cricketers, explains more about knee injuries.
HOW DOES IT HAPPEN?
Too much strain is put on the knee.
Bowlers tend to suffer from knee injuries more than batsmen.
The cartilage is the knee's shock absorber, protecting the joints from serious day-to-day damage.
Fast bowlers put a lot of pressure on their knees in their delivery stride.
Sometimes the cartilage is torn because the knee is twisted or placed under too much pressure.
Often the cartilage becomes damaged because of general wear and tear which happens over time.
HOW MANY CARTILAGES ARE THERE IN THE KNEE?
There are two cartilages around the knee - one on the inside and one on the outside.
There is also the hyaline cartilage, which is found at the ends of the bone.
This slippery tissue allows the bone to move around the knee joint without causing damage to other bones.
There is no blood supply to the cartilage, so if it becomes damaged, the tissue cannot repair itself.
The most common operation to treat a torn cartilage is through keyhole surgery.
Two very small holes, about eight millimetres in size, are made either side of the kneecap.
In one hole the surgeon will put a very small camera to look around and see exactly where the tear is.
And through the other they will place their instruments to remove the damaged tissue.
Keyhole surgery is usually completed in a day.
It depends on how serious the injury is and the course of physiotherapy to get back to full fitness.
An athlete can expect to return to fitness in six to eight weeks after straight forward cartilage surgery.
But someone who has undergone treatment for cartilage wear and tear can expect to be out of action for up to three months.