Rooney's fracture of the fourth metatarsal, appears to have been caused by trauma. Most stress fractures occur in the second and fifth metatarsal. Stress fractures of the metatarsals are also more distal (away from the ankle) as compared to acute or Jones fractures that occur more proximally (towards the ankle).
The area of the foot that Rooney clutched was closer to the ankle. Rooney running full tilt at 30 kmh, got bumped off his stride with his foot getting caught by the defender's left leg , made an awkward hop of about two and a half feet with his right foot to avoid the defender's tackling right leg, Rooney landed on the outside part of the right forefoot on impact and immediately crumpled, with his body weight borne right on top of that area (he was on one leg), all 80 kgs. (See video)
At an approximate initial velocity of 30 kmh, Rooney decelerated to avoid the tackle and hit the ground at 20 kmh , all in about two and a half feet, landing on his right forefoot. With 80 kgs of body weight. That amounts to about 1920 Newtons of force crashing down on a small area. Or in more prosaic terms his foot was smashed by an object weighing 200 kgs dropping down on it.
Ouch! That hurts. Normally that 200 kgs of weight would have been spread over the five metatarsals, with the first metatarsal bearing a good part of it, dissipating the force. But the fourth metatarsal probably bore the brunt of it by the way Rooney landed on his foot. It just snapped.
What this means is that his fracture will take longer to heal than a stress fracture. For treatment of proximal fourth metatarsal injuries to be successful, ideal treatment appears to involve non-weightbearing below-knee cast/boot immobilization for three weeks. This is followed by an additional three or more weeks of weightbearing immobilization. Healing may still be prolonged.
Rooney's chances of making it to this World Cup are negligible. Sven Goran Eriksson might have to activate Peter Crouch. He is good off the air and has been a thorn in Liverpool's opponents.