Songfacts®:

• The Sacroiliac is the tailbone (sort of - it's actually a joint that connects two bones down there), so "The Sacro-Iliac" is a dance where you just sit on your butt.
  
  It's a fitting song for 10cc, four wildly talented musicians who never ascribed to the rock star lifestyle and were always most comfortable in the studio making very inventive music with a keen sense of humor. This is their kind of dance.
• Band members Graham Gouldman and Kevin Godley wrote this song and shared lead vocals. This was an unusual pairing, as Gouldman usually teamed with Eric Stewart and Godley with Lol Creme.
• With a loping bassline, about the only way to dance to this song is to take a seat, so mission accomplished. In the lyric, they mention tow dances they won't be doing: The Swim and The Boogaloo.