Miguel Mena, the leading rider with 55 wins at the Fair Grounds meet entering Friday’s races, could be out of action for as long as six months after breaking his right ankle and heel in a three-horse accident in Thursday’s eighth race. Kerwin Clark, whose mount, Ellashoo, broke down on the lead, spurring the chain reaction, suffered more serious injuries, breaking his jaw and at least one rib, which led to a collapsed lung. Clark, a 58-year-old with more than 3,000 North American wins, had surgery Friday to repair the jaw injury, according to his agent, Charles Ashy Jr. A tube was inserted into his chest to reinflate his lung. “Everything is going as well as it could have gone,” Ashy said. Clark’s mount, a 4-year-old filly bred and owned by Rockin’ H Farm and trained by Sarah Delaney, broke down badly and had to be euthanized. The other two horses walked off the track without serious injury, as did the third jockey involved in the spill, Gabriel Saez. Mena, according to agent Richie Price, won’t have a firm timetable for his return until the swelling around his injury subsides and he sees a specialist late next week. In addition to losing the chance to win his first Fair Grounds riding title, Mena, 31, will miss the mount on Bravazo in the $1 million Louisiana Derby on March 24. Mena rode Bravazo to victory last month in the Risen Star Stakes.