The results of Daniel Hudson's MRI are in, and they're not good:
Gibson says Hudson has a UCL tear.— Nick Piecoro (@nickpiecoro) June 27, 2012
This probably means Tommy John surgery for Hudson, which is both bad and good news. The former, in that this will write off the 2012, and in all likelihood, a significant chnk the 2013 season as well. The latter, in that the surgery is becoming ever more commonplace and a full recovery from it is entirely possible. Witness Jarrod Parker, who had the operation in October 2009, and has bounced back very well. If you're interested in the specifics, I refer you to an article (warning: contains somewhat gory content) on Tommy John surgery I wrote at the time Parker went under the knife, which covers the injury, what happens in surgery, and the rehab process.
However, whether Hudson will follow the same path remains to be seen. Reports suggest he'll be getting a second opinion - it wouldn't surprise me if this was from the most well-known specialist in the field, Dr. James Andrews [now apparently confirmed by Nick P]. He was also seen by the Braves' Brandon Beachy, before he had the operation last week. If he does, it's generally seen as requiring a full 12 months before a pitcher can take the mound properly, and there's generally a period of adjustment thereafter. Parker missed the entire year after his operation, and it was 18 months before he saw competitive action again.
Assuming the diagnosis is confirmed - and, to be blunt, the alternatives seem very, very limited - what does this mean for the Diamondbacks rotation? The likelihood is that it will become Kennedy, Cahill, Miley, Bauer, Collmenter for the present. Then, when Joe Saunders returns, and there's been no official word of when that might be, or information regarding his diagnosis, it would seem likely that he'll replace Collmenter. If Collmenter struggles in the rotation, as he did in April, then Patrick Corbin may get another shot.
This leaves just Kennedy and Cahill as having been permanent residents of the 2012 Arizona Diamondbacks rotation since Opening Day. The need for a team to possess depth in its starting pitching has certainly been illustrated by the past few days: we'll see how strong Arizona are in this department over the coming schedule.