Free article on BP:

"The panic seems to have passed in St. Louis, as Chris Carpenter was cleared to begin working towards his next start. The Cardinals have juggled their rotation to cover the start he'll miss this weekend, with the plan being to slot him back in on Tuesday. Most of the descriptions of what's going on with Carpenter, including this one from Matthew Leach, have the anti-inflammatories getting the range of motion back in Carpenter's arm. The symptoms match up well with bone chips, so the worst-case scenario is a recurrence of this type of situation that necessitates surgery. Carpenter has had bone chips removed from this elbow before, so a recurrence is almost expected. The team is doing a bit of ostriching on this in not taking an MRI, but in part that could be because they have a solid diagnosis and plan. Other pitchers, such as Kelvim Escobar and Johan Santana, have come back from this type of problem quickly, and Escobar is probably the best comp here."

http://www.baseballprospectus.com/article.php?articleid=6072

The bone chip analysis does seem to fit in Carp's, in my medical opinion as well.  Bone chips occur when stress on the inside of the elbow causes impaction of top of the ulna (lower arm bone)onto the the bottom of the humerus (upper arm bone) at the joint surface, possibly scraping some bone/cartilage away.  This cartilage/bone stuff can float around in the joint and occasionally get stuck, causing swelling.

As long as its not the UCL (Tommy John ligament), I'm completely unalarmed.  Problem is, Carp could end up needing his elbow scoped out sometime this season, which would likely shelf him for 4-6 weeks.

Carp's bullpen session and next 2 outings will be crucial, IMHO.