I've looked everywhere; there are a handful of articles I found online that allude to Saint-Just receiving a (minor?) sabre wound at the time of Robespierre's jaw wound during their arrest the night of 9 Thermidor (July 27), 1794. I have reason to believe that it was a minor wound because several books and articles I've looked at emphasize the fact that Saint-Just was the only Robespierre supporter who was able to walk by himself after the violent arrest. The movies seem to either ignore it or quickly gloss over it, being of no help.
I did find a book and article that gave me a (primary?) source: Gazette d'un parisien sous la revolution by Ruault, pp. 357-61 (as cited by Dwyer, et al., The French Revolution and Napoleon: A Sourcebook). Unfortunately, I haven't been able to locate a copy of the Gazette that I can look at (and anyway, I don't speak or read French), and it seems odd that it should say simply "Saint-Just was sabred" while it gives all the gruesome details of everyone else's wounds ("One of Hanriot's eyes was hanging out of his head," for example). Other books and articles I've found claim that Saint-Just was "unscathed".
There are other discrepancies, too; namely that most American sources claim Robespierre's wound was a botched attempt at suicide, while most European sources claim it was sustained when rebel soldiers burst into the Hotel de Ville and fired shots. I'm going to lean in favor of the European version, I think. There seems to be more evidence to back it up.
Anyway, any help on where on his body Saint-Just was wounded (arm? leg? torso?) and its severity would be of much help. Thank you!