They opened up his shoulder, and they found Jack Wilshere!
According to a press release on Arsenal's official club website, Swiss international center half Johan Djourou will return to the training ground in one month after having exploratory surgery on his dislocated shoulder. Most onlookers originally considered him out for the rest of the season.
What this means, basically, is that Djourou could conceivably be ready to play in time for Manchester United visiting the Emirates on Sunday, May 1. The Bolton match on Sunday, April 24 may be a bit of a reach, but if Djourou can be back to match fitness in time for the Man U game, it could offer a big boost to Arsenal at the climax of the season.
This assertion / hope / invocation of the gods, of course, assumes quite a lot: 1) that Djourou won't have as torrid a time along with his teammates as they had against Manchester United in the FA Cup two weekends ago, when the Red Devils countered with excellent effect up the flanks; 2) that Arsenal and Manchester United will be within mathematical touching distance, which is possible, but in question; 3) that an alien scout ship does not decide to land on London Colney between now and May Day, subordinating the inhabitants of northwestern London to its will and, more pertinently, landing on top of Djourou and Robin van Persie, dislocating the former's other shoulder and spraining the latter's ankle.
Assuming May doesn't usher in the era of supra-Cockney overlords, though, the return of Djourou for possibly four Premier League matches at the end of the season cannot hurt.