Purdedel and WinStar Stable's Sharp Humor has been diagnosed with a small fracture of the left knee which will knock him off the Triple Crown trail.The 3-year-old New York-bred son of Distorted Humor is scheduled to undergo surgery Thursday to repair the fracture.A statement from the owners said the injury was detected during an examination following the colt's 19th place finish in the 20-horse field that contested Saturday's Kentucky Derby Presented by Yum! Brands (gr. I)."It was very unfortunate and now we know why he ran the way that he did," said trainer Dale Romans. "He just didn't run his race at all."Winner of two New York-bred stakes as a 2-year-old, Sharp Humor won the Swale Stakes (gr. II) before finishing second in the Florida Derby (gr. I) victory of Barbaro, the undefeated Kentucky Derby winner."We now know how good both Barbaro and Sharp Humor are, so we have very high expectations for this colt," said Romans.