Updated to add report on the surgery:

Barbaro broke three bones in his right hind leg, and dislocated what was left of his fetlock to boot. One of the bones that fractured was the sesamoid bone; this is the bone that Ruffian broke in 1975, causing her to be put down. She's buried at the finish line in Belmont Park. When people ask for my sports heros, I always say "Ruffian, and they shot her." It's a little Thelma and Louise, but it's also quite true.

But meanwhile, back on topic, the sesamoid bone is particularly difficult to treat because it works like a pulley with the tendons sliding over it. Any disruption to the sesamoid means that the ankle essentially flops without control, allowing the leg to touch the ground, and loose bone shards can sever the tendons, which is an even more difficult injury to come back from. As well, the sesamoid bears several times the horse's body weight in pressure with each step, so it must be strong enough to stand up to pressure of several tons. The long healing period that could make this possible is the very thing that is impossible. Probably the best thing at this point would be to replace, rather than attempt to repair, the bone.

Update: They've attempted to fuse the joint, which means he'll be able to walk but his racing days, of course, are over. It's as if his right rear leg will be wearing a high-heeled shoe for the rest of his life, while the others wear Nike Air. The entire pastern functions as a shock absorber, which you can see in dressage or in slow-motion replays of racing. Now all the shock will be directed to his hock and his hip, putting them at risk for future injuries, but a life at comfortable stud should be perfectly possible for him, provided he doesn't mess up his recovery.

Note that the actual reason Ruffian had to be put down was not the sesamoid injury per se, but rather the damage she did to herself when she came out of anesthesia. Equine medicine has become much more sophisticated since then, but it remains to be seen what will happen with Barbaro. He is already walking. So far he's calm, and he appears to be very people-oriented, which helps him during convalescence. If they ultimately have to put him down, he's a stallion and they will undoubtably take the semen for AI purposes. In this diagram, the bones Barbaro broke are F, E, and D.

Barbaro at 2:1

Barbaro emerged from seven hours of surgery Sunday night to repair life-threatening injuries and "practically jogged back to the stall,'' said Dr. Dean Richardson, who performed the procedure a day after the colt broke his right rear leg in three places at the Preakness.

But Richardsonsays it's "a coin toss'' whether the Kentucky Derby winner will survive, even though surgery went well…

"You do not see this severe injury frequently because the fact is most horses that suffer this typically are put down on the race track," said Richardson, the chief of surgery for the center. "This is rare."

"It's about as bad as it could be," he added. "The main thing going for the horse is a report that his skin was not broken at the time of injury. It's a testament to the care given to the team of doctors on the track and [jockey] Mr. Prado on the racetrack."

Richardson outlined Barbaro's medical problems: a broken cannon bone above the ankle, a broken sesamoid bone behind the ankle and a broken long pastern bone below the ankle. The fetlock joint — the ankle — was dislocated.

"The aspects of the surgery will be dictated slightly by what we find," Richardson said. "But the bottom line is we will attempt to perform a fusion of that joint and to stabilize it and make it comfortable enough for him to walk on."