ABOARD THE PAPAL PLANE >> Pope Francis acknowledged Saturday that he no longer can travel like he used to because of his strained knee ligaments, saying his weeklong Canadian pilgrimage was “a bit of a test” that showed he needs to slow down and one day possibly retire.

Speaking to reporters while traveling home from northern Nunavut, the 85-year-old Francis stressed that he hadn’t thought about resigning but said “the door is open” and there was nothing wrong with a pope stepping down.

Francis said that though he hadn’t considered resigning until now, he realizes he has to at least slow down.

Francis was peppered with questions about the future of his pontificate following the first trip in which he used a wheelchair, walker and cane to get around.

He strained his right knee ligaments earlier this year.

In other comments, he:

• Agreed that the attempt to eliminate Indigenous culture in Canada through a church-run residential school system amounted to a cultural “genocide.” Francis said he didn’t use the term during his Canada trip because it didn’t come to mind. Canada’s Truth and Reconciliation Commission determined in 2015 that the forced removal of Indigenous children from their homes and placement in church-run residential schools to assimilate them into Christian, Canadian constituted a “cultural genocide.”

“It’s true I didn’t use the word because it didn’t come to mind, but I described genocide, no?”

• Suggested he was not opposed to a development of Catholic doctrine on the use of contraception. Church teaching prohibits artificial contraception. Francis noted that a Vatican think tank recently published the acts of a congress where a modification to the church’s absolute “no” was discussed.