I've had my fair share of MRIs done, and while I'm not a doctor, there are several things I've learned along the years about MRIs vs. X-Rays, or even CT:
1. An MRI machine is SUBSTANTIALLY more expensive than X-ray (couple of million of dollars vs. several thousands), and the test is also substantially more expensive.
2. An MRI test takes longer, 15-20 minutes vs. seconds
3. An MRI machine requires higher trained techs
4. An MRI test may require contrast (though not always), which complicates things
5. If contrast is required, blood test will also need to be drawn to determine kidney functinality (to make sure your kidneys can filter out the chemical in the contrast) - that blood work, unless done in an E.R., will never come back within minutes - probably next day.
6. Lastly, give the all of the above, orthopedic injuries are not life threatening (unless we're talking neck/spine here), and therefore can wait until the player gets back to his team's base, and have it done at the local/trusted hospital. Anything life threatening, like a head or spine injury, and the player would get transferred immeidately to the local hospital at that city, and not wait for the trip back home.
Now side questions: Can anyone recall a player who was suspected to have torn his ACL/MCL, but was later on (via MRI) it was found to have been just a bad sprain? In other words, I'm trying to guage how reliable these prelimnary 'suspiciouns' are on averag, when it comes to a knee injury, before an MRI was actually performed.