Are knee injures commonly sprains and torn ligaments, or are breaks more common? what is usually ordered for diagnostic info- mri or x-ray?

All three: More common to see soft tissue injuries such as ligament tears (most severe form of a sprain, and sprains than a fracture. But all three occur fairly commonly with trauma or sport related injuries. Mri is best for evaluation of soft tissue injuries where as x- ray can be very effective to evaluate boney injuries such as fractures. Seek care with an orthopedic surgeon.

Sprains: Sprains are most common overall. They range from mild to severe. In severe sprains there is actual ligament tear. Most knee injuries can be diagnosed by a good physical exam. X-rays are usually sufficient if there is concern for a fracture. Mri's tend to be reserved for later if a suspected sprain does not heal as expected, or if there is concern for a meniscus or ligament tear.