In the 12th inning of Game 1 of the American League Championship Series versus the Detroit Tigers, Yankee great Derek Jeter made what seemed to be a routine play on a ground ball by Detroit’s Johnny Peralta. Instead, Jeter failed to get up after diving/falling during the play. X-rays taken after the injury showed a fracture in his ankle. There is still speculation as to which bone Jeter fractured. The ankle is a joint that is made up the fibula, the bone on the outside part of the lower leg; the tibia, the bone on the inside part of the lower leg; and the talus which is a bone of the foot. The fibula and tibia form an upside down, offset “Y” (the fibula goes lower than the tibia), and the talus sits in the open end of the “Y”. The talus has a rounded surface that allows your ankle to move up and down. As “ankle” fractures go, the fibula is the more common of the two to fracture due to its lesser size and capacity to withstand impact/torsional forces. A fracture of both bones is more severe an injury and recovery can be prolonged depending on how the bone “knits” back together. A fracture of either the tibia or fibula can also be severe requiring plates and/or screws to repair.It has been widely reported that Jeter had had a bone bruise on the same leg back in September and a more recent bone bruise in his foot after fouling off a ball onto it. The mechanism of the bone bruise in September has not been reported. A bone bruise is considered a micro-fracture ofthe medullary portion of the bone and can be accompanied by both bleeding and swelling. Unlike actual fractures, bone bruises cannot be picked up on x-ray and were first detected due to the signal changes evident on MRI. A couple of studies have looked at the symptoms associated with a bone bruise and their severity. One study looking at bone bruises caused by enough force to rupture an anterior cruciate ligament of the knee (imagine a football player’s knee being hit by a helmet) and found that the bone bruise could continue to cause pain for up to 5 years. Another looking at the forces required to tear the medial collateral ligament of the knee only found that pain could remain for 3 to 6 months.A good analogy to visualize a bone bruise versus a fracture would be shooting a puck at a pane of plexi-glass versus regular glass. When apuck breaks plexi-glass, there are no big breaks, just a series of small ones moving out from the centre of impact but the plexi-glass still holding together. Contrast this with regular glass that breaks into large and small chunks with the glass falling apart. Many pundits are speculating that the original bone bruise may have progressed to a stress fracture and ultimately to a frank fracture of the bone. Stress fractures can be categorized into fatigue or insufficiency (or a combination of the two). A fatigue fracture suggests normal bone with abnormal, prolonged forces applied to it (common in runners, army recruits …) while insufficiency fractures are normal stresses applied to abnormal bone (common in the elderly with compression fractures due to osteoporosis). A bone bruise could be considered abnormal bone and if played on long enough, as Jeter did by continuing to play through September and October, the case could be made that a stress fracture developed and that the play he made in the 12th inning was enough to cause a full fracture to the bone. If this is the cause of Jeter’s fracture, the Yankee’s medical staff may have caused the loss of their captain by mismanaging his original injury – the bone bruise in September – and ultimately losing him for the rest of the season and possibly their chance to go to the World Series.