About a decade ago, I got a text from Peter Gammons. "When did baseball players start having obliques?" Peter knew that players had always had the muscle, but it did seem that we were suddenly seeing more of them injured about that time. This year, it seems to be rib injuries that are the hot new thing in training rooms around the league.
Anatomically, there's no difference. Ribs are ribs, and we have to assume that in almost all cases, MLB players have normal ribs in structure and strength. The game is also much the same—at least in terms of the stresses that it places on the ribs.
We then have to look at the method of injury in context. For Troy Tulowitzki, he was injured on a diving stop of a grounder while at shortstop. Ian Kinsler injured himself twisting away from an inside pitch at the plate, though many point to an awkward headfirst slide earlier in the game as a possible injury point. Pitcher Jake Peavy of the White Sox is a bit tougher to pin down, as he was lifted early but showed poor velocity all through the last start he made before heading to the DL.
One interesting point on all these is that the diagnosis wasn't simple. In each case, an MRI was necessary, and in both Kinsler and Peavy's case, X-rays were negative. Simple rib fractures—the result of collisions—tend to be very visible on X-rays, so that fact tells us that the fractures are either small or in an unusual location.
There are other rib injuries around the league, with Edwin Nunez of the Yankees and Josh Kinney of the Mariners also listed, but those go less noticed, in large part because they're not All-Star-caliber players like Tulowitzki, Kinsler and Peavy.
In other words, this may well be a cluster of injuries that is noticeable due to the player's visibility and notoriety rather than an increase in the incidence of the injury itself. Looking through my database of injuries, there is only a slight increase over previous seasons. This seems to be random variation, which is typical of traumatic injuries like this.
Last season, there were six ACL sprains in MLB, but this year only two (and one of those was a flukish recurrence). There is almost no known way of preventing these kinds of injuries, so the focus is on reducing the rehab time necessary.
It appears to be much the same way for rib fractures.
Injuries will happen, on dives, odd pitches or strange swings, but it's up to the medical staff to minimize the time lost. Getting Kinsler, Tulowitzki and Peavy back just a week early could have huge implications for their team.
For example, Kinsler has been worth about a win every 20 games played, so a week is worth around one-third of a win. All you have to do is think back to last season's AL West finish to know how valuable that can be.
There is no answer to why there are more rib injuries because, simply put, there really aren't more. Traumatic injuries are inconvenient and unpredictable, even for big stars like these.