Caitlyn Jenner's days as an Olympic star have caught up to her in a painful way -- in the form of knee replacement surgery.
Sources with direct knowledge tell TMZ ... the decathlon gold medalist went under the knife at Cedars-Sinai in L.A. December 14. We're told the surgery lasted 3 hours and so far, so good.
The before-and-after X-Rays pretty much tell the story.
Caitlyn's up and about again ... walking gingerly around her Malibu compound, where she's staying for at least another week before venturing out.
Her goal right at the start of 2022 ... to walk normally, drive and get back to all the stuff she likes ... including golf. She loves skiing -- something that was off the table before surgery -- but her goal is to hit the slopes next winter.
Fact is ... she's needed a knee replacement for a while -- 25 years to be exact. The pain, we're told, has been excruciating at times and Caitlyn knows it emanates from her training for the '76 games.