Guess I got confused by the mention of ribs and shoulder blade, the chronology seemed a bit off.
I'm not entirely sure how Gigue would be able to correct the diagnol force without a hand behind Sigurd's back, like I said. The amount of strength required to direct Sigurd straight down using the leverage on his belt would be insane because Gigue would also have to counter his own body weight pulling him rightward. It would literally require him to be able to throw Sigurd to the ground with what amounts to a curtain opening motion, which are not strong muscles on the human body, though I'm sure Gigue is better at the peck machine than I am it's still a tall order considering Sigurd's weight and position. Also I'm not convinced the belt would even sustain that much force, I'd assume it would give out under that sort of power.
@Drifting Pollen can you take a look at this from a neutral perspective, I'm not well versed in grappling so I can't tell if what I'm saying makes sense, but it seems a little unnatural for Sigurd to fall face down while Gigue is holding onto him in that fashion.
Also, though it's probably not a significant factor, you do have to consider both Gigue's arms are at least somewhat weakened by injuries by this point, directing Sigurd's fall from this position -seems- difficult to me.