Vatican: Pope Francis is tired after whirlwind, limping a bit, but doing fine

Concluding one of the longest and most event-filled trips of his papacy, Pope Francis was looking weary and walking with a limp Saturday in Philadelphia.

But the Vatican assured reporters the pontiff, who turns 79 in December, is a just little taxed and remains in high spirits.

"Obviously, with a trip like this — it's very engaging, a lot of work, fatigue — we can understand if he is a little tired physically," Vatican spokesperson Federico Lombardi told reporters Saturday in Philadelphia, the final stop of the pontiff's 9-day trip to Cuba and the U.S. that ends Sunday.

Francis has clearly been walking with a limp in recent days and appeared to stumble while walking slowly up stairs to embark on a flight from New York to Philadelphia on Saturday morning.

"He was tripping on his cassock," Vatican spokesman Thomas Rosica said, referring to the white vestment the pope wears. "He was carrying the bag and didn't lift up the robe. So he kind of lunged forward twice. I do the same thing when I have the vestments on and I don't lift them up."

The pontiff is known to suffer from a bad knee and sciatica, a nerve condition that can radiate pain from the lower back down the hips and to the legs. Rosica said it's a minor condition. "There's nothing serious whatsoever," he said.

The pope, Rosica said, is thoroughly enjoying this trip. "He loves it. He's thrilled. Watch his face. The face says everything," Rosica said. "He's really happy."