Not to sound arrogant, but I actually am a doctor (family medicince resident) and here are my two cents: MRIs are great, but they depend on the quality of the study (how much the patient moves, etc) and the person reading it. It sounds like they got 2 opinions on the read, and based on that the MRI didnt show the injury. As an isolated incident, not worth calling for the medical staff's collective head (but bad news for Baker and the Twins). But, with everything that has happened recently with injuries (especially 2011) it makes me wonder about the Twins medical staff. There seemed to be a lot of misdiagnosed, mistreated, undertreated and/or questionable medical decisions made (ie. bilateral leg weakness).
Again, Im not a radiologist or surgeon, so Im far from an expert.