The 23-year-old singer, along with Pataky, who is married to Chris Hemsworth, and two of their friends, chose to have a "custom wave" etched into different areas of their body, reported Ace Showbiz.
Artist Lauren Winzer was delighted that the stars and their pals walked into her tattoo parlour in Sydney, Australia, to have the work done and took to Instagram to share a picture of her creations.
Alongside the image, Lauren wrote: "Stoked to do these little matching custom waves @kellyslater drew up for @mileycyrus @kalanimiller @elsapatakyconfidential @aprilmun(sic)."