By Gennady Fyodorov Jan 31 (Reuters) - Former Olympic champion Yevgeny Plushenko underwent successful back surgery in Tel Aviv on Thursday to replace a deteriorated disc in his spine. "Yevgeny had an operation to remove one of his spinal discs with a synthetic one," the Russian's long-time coach Alexei Mishin told Reuters. "The doctor who performed the operation said it was a success (but) ... it's too early to make any prognosis about his return to the ice."