Jaroslaw Kaczynski, the leader of Poland's right-wing ruling party, has undergone a medical procedure on his knee and now faces rehabilitation.

Party spokesman Beata Mazurek said Thursday that the source of Kaczynski's ailment is osteoarthritis. She said it is not yet clear how long his period of rehabilitation will last.

The 68-year-old Kaczynski is Poland's most powerful politician, shaping policies and selecting prime ministers from behind the scenes even though the only elected position he holds is that of parliamentary lawmaker.

Kaczynski, who had been limping recently, has been hospitalized since early May. His absence has led to speculation that his strong leadership role could be weakening.

His aides denied that this week, saying he remains on top of political decisions and has no plans to retire.