BERLIN (AP) — A Berlin zoo says four young Sumatran tigers are undergoing treatment for knee problems.

The quadruplets were born in the summer of 2018 and as they started to develop, zookeepers noticed abnormalities in the way the cubs ran, the Tierpark Berlin said Wednesday.

CT scans revealed all four tigers had knee misalignments that were causing cartilage damage.

That damage is now being treated, and an expert team is to sit down in the new year to discuss long-term strategies to help the tigers.

“We don't want to just rely on our own judgement. We will sit down with other experts,” zoo manager Christian Kern said. “Animal welfare is our top priority.”

Aside from their knee problems, the animals - males Willi and Oscar and females Seri and Kiara - are doing well, exhibiting normal eating habits and playing with each other, according to the zoo.

The parents of the quadruplets, Harfan and Mayang, have lived at Tierpark Berlin since 2013.