If a patient comes in with knee pain that he describes as deep, sometimes radiating, sharp, but sometimes deep aching and he has no pain with the physical exam, which would you order him to look for any damage, and why- an mri or an mri arthrogram?

MRI: I'd recommend the MRI alone as it's noninvasive,uses no dye, and gives a good image of the internal structures of the knee joint.

Start with an MRI without arthrogram. The knee joint is quite sensitive to almost all injuries, and produces fluid (called an effusion) in most cases. The fluid is almost like water, and is a natural contrast agent.