Jan. 28 (Bloomberg) -- Kentucky Derby winner Barbaro underwent surgery to treat an abscess in his right hind foot that carries ``significant risk'' of a fracture to the colt's left hind leg, chief surgeon Dean Richardson said today.

``He had a perfect recovery from anesthesia and has been in and out of the sling since then,'' Richardson said in a statement after yesterday's surgery. ``His left hind foot appears to be stable at this time. We will continue to treat Barbaro aggressively as long as he remains bright, alert and eating.''

The four-year-old horse, whose undefeated racing career ended when he shattered his right hind ankle in the 2006 Preakness Stakes, developed an abscess from a bruise he got fighting discomfort from laminitis in the left hind leg, Richardson said. Since the accident May 20, the colt's ankle had healed during his recovery at the University of Pennsylvania's George D. Widener Hospital in Kennett Square, Pennsylvania.

``This is another significant setback that exemplifies how complex his medical situation remains because both hind limbs have major problems,'' Richardson said. ``We remain concerned about both front feet. Remarkably, his attitude and appetite were excellent overnight.''

`Only Option'

During surgery to place an external device on the bruised foot, Richardson inserted two steel pins transversely through the cannon bone, which is the long bone in the front part of the lower leg. Those pins are connected to external sidebars which link to a lightweight alloy foot plate to eliminate all weight bearing on that foot.

``There is significant risk in this approach but we believed it was our only option given the worsening of the right hind foot problem'' Richardson said. ``The major risk of the external skeletal fixation device is that the bone bearing the weight can fracture.''

Barbaro got laminitis, a life-threatening inflammation that often afflicts a limb that is supporting more weight than usual, in his left hind foot in July. Richardson removed 80 percent of the hoof wall at that time, and removed additional damaged tissue in January.

The right hind foot developed ``a deep subsolar abscess secondary to bruising when he went through a period of discomfort on the left hind foot,'' according to the hospital's statement. ``It is not laminitis but the undermining of the sole and part of the lateral heel region are potentially just as serious.''

Richardson attempted to treat the problem with a cast and then a custom-fabricated brace. He decided to use the external device because he needed access to the area for treatment. Barbaro spends part of his day in a sling.

To contact the reporter on this story: Nancy Kercheval in Washington at nkercheval@bloomberg.net.

Last Updated: January 28, 2007 11:18 EST