This type of injury is easily diagnosed using clinical examination. X-rays are usually done to ensure that there is no fracture of the ribs, and an MRI can be used to determine that there is no cartilage damage and also to positively ID the sprain and its exact severity.
Treatment for the injury is simple. Since a strain is a mild muscular injury, it is treated with rest, ice, anti-inflammatories, and gentle stretching exercises. Most importantly, the athlete must try to limit the movement of the torso, because each bend or stretch can further tear or limit the healing of the ribcage muscles.
Stretching exercises that are done daily can help to avoid this type of injury, but nothing can be done to truly prevent it. The best stretches for this muscle group are side-bending exercises and side bending with rotation. These are the exercises most often done by kids by spreading the legs, spreading the arms like a scarecrow, and turning one way and the other from the waist. The other is done by bending forward during these exercises.
For a full recovery, athletes usually need about six weeks. Hundley came off the DL after less than four weeks, missing 24 games, and appears to be recovering nicely. He may play with some protective taping wrapped around the ribcage, which serves as more of a mental reminder than an actual protector.
Hundley should be as healthy and able as he was before the injury. But, there is, as in the case of most sprains, a slightly increased risk of him reinjuring the ribs at some point this season. Because he throws righthanded, he will lose some power and accuracy on his throws to second, and he will probably feel a little bit of pain because the motion of lifting his arm and then quickly pulling it down taxes the ribcage muscles.