DS wasn't posterior but i had a lot of back pain & tried the injections. i found them to be extremely painful - it was pretty much the only time during my labour that i yelped/made any noise & i think i nearly broke DP's hand! the worst bit was that they did nothing to ease the back pain - on a scale of 1-10 the pain eased by about .5 the midwife had asked me to give the back pain on a scale of 1-10 & i gave it a 7 or 8. after the injections i told her that i now knew what 10 felt like, that's how painful they were...my own fault she did warn me that they'd sting

it may work better for others b/c everyone is different, but i certainly wouldn't try them again