Foot notes: The metatarsal mystery

Sam Singh is shaking hands with my foot when he tells me I've got an arthritic big toe. "See, you've only got 30 degrees flexion and it should be 90," he says, wiggling the offending digit. What can be done about it, I ask? He lets go of my foot and mimes a hammer hitting a chisel, an eager smile spreading across his face. All I can think of are the workmen I'd seen outside the hospital, chewing up the pavement with pneumatic drills.

The consolation is that my semi-crippled toe poses no threat to England's chances in the World Cup. It is Wayne Rooney's fractured metatarsal that has brought me to Mr Singh, one of only six orthopaedic surgeons in London who specialise in foot and ankle problems. He prods my feet and briefs me on the 26 bones in each. The toes are called phalanges, he explains, rummaging in his briefcase for a skeletal model. Without the surrounding flesh, they clearly link to the five metatarsals. The talus, he continues, sits beneath the ankle and plays a crucial role in transmitting our weight in an arc from the heel to the ball of the big toe.

The fourth metatarsal, the one Rooney cracked, twice, is not supposed to bear this weight. Its job is to maintain the arch, which acts as a shock absorber. Together, these bones, their 107 ligaments and 19 muscles form an elegant structure. It is, Mr Singh says proudly, a far more energy-efficient way of moving around than the petrol engine.

Yet the foot has an image problem. It is famous for smelling like Limburger cheese, for athlete's foot and for fragile bones that endanger the nation's self-esteem. The metatarsal, in particular, is getting a reputation as the foot's wimp. Since David Beckham cracked his second metatarsal in a Champions League game just weeks before the 2002 World Cup, nine other top players have suffered fractures. Combined, these 10 players have taken more than three years out of the game.

Doctors caring for million-pound footballers don't skimp on the treatments. In addition to a sensible, inflatable cast to immobilise the fracture, they often try to hasten healing by prescribing ultrasound, electric bone stimulation and hyperbaric tents, in which the patients breathe air with a high concentration of oxygen. But the evidence for these exotic treatments doing much good is weak. Mere mortals are likely to get a simpler regime. Daniel Weiner, 24, a trainee lawyer, broke his fifth metatarsal during a holiday in Israel. "The doctors were quite dismissive," he says. So when the pain returned after a visit to a gym last week, he went to see Mr Singh in his private practice at the London Bridge Hospital. "He put me in plaster up to my knee and told me to stay off it," Mr Weiner says. If the bone hasn't healed within four weeks, they'll discuss operating to put in a plate or pin.

At three inches (7.5cm), metatarsals are the longest bones in the foot, and that makes them vulnerable to stress fractures. Sometimes these are called "march" fractures because they often strike army recruits who have been burdened with 50kg of kit and ordered to pound a parade ground. Foot-and-ankle specialists have other worries, too, from hammer toes and bunions to strains, sprains and torn ligaments. Although metatarsals get the most public attention, 40 per cent of disorders involve the big toe. Half the problems, particularly among women, arise from wearing shoes that are too narrow, too high or both.

The human foot is an oddity in nature. No other creature has anything that works quite like it. "It's an utterly unique way of walking around," says Dr Will Harcourt-Smith, a paleoanthropologist at the American Museum of Natural History in New York. Even other bipeds have quite different styles of moving. "Birds hop and Tyrannosaurus rex kept its body horizontal, but our bodies are upright." The secret is the foot's unusual evolutionary path. Until 3.7 million years ago, our ancestors lived in trees, their hands and feet adapted to grasp branches. As they descended to live on the ground, their big toes became fixed for stability, their ankles became more robust to take the full weight of the body, their metatarsals arched to form a spring, and a locking mechanism evolved that turns the whole structure into a powerful lever.

The first evidence of us walking upright comes from fossil footprints in Laetoli, Tanzania, discovered by Mary Leaky. They show two of our Australopithecus afarensis ancestors walking across a plain of volcanic ash in much the same way that we walk today. Their skulls, however, would still have been tiny.

Why we began to stand erect is a matter of debate. Dr Harcourt-Smith thinks it helped our ancestors find food and stay cool as the jungles were slowly replaced by grassland. But the fossil record is clear about one thing, he says: "Walking on two legs is the first thing that happens to us as we become human."

When we stand still, the foot has a simple job, says Mike O'Neil, a podiatric surgeon in London. It distributes weight through a stable tripod of contact points - the heel and the balls of the toes. But when we're moving, in what's called the gait cycle, it has more to do. Each stride begins with the heel strike, cushioned by a thick layer of fat. As the body's centre of mass moves forward, the weight shifts to the side of the foot and the knobby end of the fifth metatarsal. The foot then rolls inwards, which transfers the weight to the first metatarsal and locks the bones into place. At the same time, three muscles attached above and below the knee pull the Achilles tendon, raising the heel and preparing the foot to push off again from the toes.

Because bones are associated with death, we tend to think of them as solid and inanimate. In fact, within the smooth outer surface, they're mostly sponge-like and riddled with cells. Some are constantly breaking down old bone structure, others building new hard bits. It's these cells that repair fractures. Adult bones can become stronger, too. X-rays of professional tennis players show that the bones in their racquet arms are thicker. Paul Jackson, an orthopedic physician in Bath, says most of the foot injuries he treats are among runners training for the marathon who increase their mileage too quickly: "They're ready in cardiovascular terms, but their bones haven't adapted."

Exactly why so many footballers have been having foot problems in recent years is hotly debated. Some blame Rooney's fractures on Nike's new Air Zoom Total 90 Supremacy boots, which he was wearing, though the company denies responsibility. Tottenham Hotspur's midfielder Danny Murphy, who has also suffered a fractured metatarsal, blames the hardness of pitches. Others note that most of the injuries happen at the end of the season to players whose teams are doing well, suggesting that the problem may be simple over-use. But perhaps the most telling observation comes from Dr Harcourt-Smith, who notes: "We haven't evolved to play football."