French Open second round: Andy Murray v Juan Ignacio Chela
Venue: Roland Garros, Paris Date: Wed, 26 May (Third match on Court One)
Coverage: Live video streamed on BBC Sport website (UK only) and BBC red button; commentary on BBC 5 live sports extra; also live on Eurosport; live text commentary on BBC Sport website
Details of BBC coverage
Murray says he has suffered from knee trouble since the age of 16
If Andy Murray is to fulfil his lifelong ambition of winning a Grand Slam title, he will have to do more than beat the likes of Roger Federer and Rafael Nadal - he will have to overcome his own body.
The star of British tennis was born with a bipartite patella - or split kneecap - and revealed after his first-round victory over Richard Gasquet at this year's French Open that the condition has been causing him pain since the age of 16.
But what exactly is a bipartite patella, why is it affecting Murray now, how should it be treated and could it prove career-threatening?
BBC Sport spoke to leading sports physician Dr Andy Franklyn-Miller for an insight into the problem afflicting the world number four.
WHAT IS A BIPARTITE PATELLA?
The split kneecap irritates the patella tendon and causes pain
In essence, it is a kneecap made up of two separate bones instead of one. During childhood, most kneecaps form as a single segment but occasionally - as seen with Murray - they form as two, fused together by fibrous tissue.
"A bipartite patella is very rare," said Dr Franklyn-Miller. "It occurs in about 1% of the population and often goes unnoticed because it is only when you exercise at the intensity of a top-level sportsman like Murray that you might see symptoms.
"It tends to be found incidentally - you would be X-raying for another reason, such as knee pain, and come across a bipartite patella - but the two bones have a very close join that normally settles down and doesn't cause any problems."
WHY, THEN, DOES MURRAY EXPERIENCE PAIN?
Scot Murray, 23, believes he played too much tennis while he was still growing and recalled how the stress on his split kneecap became so severe that "it got to the point where I couldn't walk".
Dr Franklin-Miller explained: "It's very unusual that pain would stem from the actual join between the two pieces of bone. It's more about how the separation affects the patella tendon, which attaches the kneecap to the lower leg.
"As our thigh and lower leg bones grow in adolescence, they put enormous force on the patella tendon. If you're involved in high-level sport, these forces are even greater.
"When your thigh muscle contracts, a regular kneecap will pull the patella tendon in one direction but a bipartite patella will pull it in different directions. This abnormal loading irritates and inflames the tendon, resulting in pain."
WHY IS HE TALKING ABOUT IT NOW?
Murray revealed he has trouble bending beyond a certain point and that sliding is particularly unkind to his knee. So his pain may be particularly acute during the clay-court season. A gruelling five-set battle against Gasquet on the red dirt of Roland Garros may well have prompted his comments.
"At a Grand Slam tournament, you could play as many as seven five-set matches with very little rest," added Dr Franklyn-Miller. "Tennis is all about explosive movements. The longer a match, the greater the load on your knees.
"The load through the tendon is at its greatest when you come to a sudden stop. In that sense, clay should be more forgiving than hard courts because the give in the surface acts as a shock absorber.
"But then again, clay plays slower than hard courts so there's a lot more scampering into the net, stopping sharply, bending down to retrieve low balls and twisting to get back in position."
IS MURRAY'S CONDITION DEGENERATIVE?
Not particularly. The British number one says he is experiencing the same sort of pain now as he was during his junior days at the Sanchez-Casal Academy in Barcelona.
"Murray's knee shouldn't have got any worse over the years and, provided it is managed correctly, it shouldn't do so in the years ahead," stated Dr Franklyn-Miller.
"The back of our kneecaps come into contact with the joint itself and it's possible that his bipartite patella could be roughening the cartilage, which can lead to osteoarthritis.
"But most elite athletes are susceptible to an element of osteoarthritis. Although it may affect them later in life, it is unlikely to ever cause pain during a match."
SO HIS CAREER IS NOT UNDER THREAT?
When Murray was diagnosed with his problem at the age of 16, he was forced to rest for six months. But with care and attention he can manage it through a season and it will not determine his future in the game.
"It's certainly not career threatening," insisted Dr Franklyn-Miller. "The problem with modern-day tennis is that it's a year-round sport but Murray and his team will have a routine set out for dealing with the knee and it seems to have been pretty successful so far.
"Because a bipartite patella is formed at birth, there is no cure and there is no way of predicting exactly how the condition will develop in the future.
"But Murray will have the very latest biomechanical technology available to him. That will ensure he can monitor what's going on inside the knee and treat it accordingly."
HOW WILL MURRAY BE TREATING THE PROBLEM?
The tried and trusted Rice principle (rest, ice, compression, elevation) continues to prevail. Murray's methods include Bikram yoga, ice baths and physio, all of which keep his injury at bay.
"There are a variety of techniques designed to settle the pain - like rest and use of a leg brace. You can also go down the surgical route to alter the pull of the thigh muscles or remove the second segment of bone but these are completely inappropriate to a top athlete like Murray," concluded Dr Franklyn-Miller.
"So he will probably manage inflammation with lots of icing, leg-strengthening exercises, stretching and perhaps things like shock-wave lithotripsy and simple injections of water. He will carefully manage training but the critical focus should be on recovery after matches.
"The good news for Murray and the British public, with Wimbledon coming up, is that he's fit and his strength and conditioning has improved enormously over the last five or six years, which will help to support what is a pretty unique problem in his knee."