Analysis of Andrew McCutchen's injury

For now, the Pirates are hoping Andrew McCutchen will recover without a trip to the DL. Justin K. Aller/Getty Images

When Andrew McCutchen instinctively reached for his painful left side as he trotted toward first base Sunday, the immediate culprit was deemed to be an abdominal oblique muscle, a frequent offender in the family of abdominal injuries common to both pitchers and position players.

As it turns out, the Pittsburgh Pirates' All-Star outfielder was dealing with something far less common: an avulsion fracture of one of his lower ribs. In a statement from Pirates general manager Neal Huntington, the team announced McCutchen had specifically been diagnosed with “an avulsion fracture involving the costochondral cartilage of the left 11th rib.”

The breakdown of the language describing McCutchen’s injury goes something like this. An avulsion fracture occurs when a soft tissue structure attached to bone (typically tendon or ligament) is stretched beyond its normal length and pulls away, taking a tiny piece of bone with it. In McCutchen’s case, instead of the left abdominal oblique muscle fibers tearing within the substance of the soft tissue, the attachment point at the 11th rib pulled away, taking a fleck of bone with it.

The 11th rib is what is considered a floating rib as it does not attach on the front side of the rib cage (ribs 11-12 are both floaters). The rib structure is not just pure bone, however. The bone joins with a piece of cartilage on the front end. The costochondral junction is where the rib (costo) and the cartilage (chondral) meet and form a small joint. In McCutchen’s case, the news that his avulsion fracture involved the costochondral cartilage indicates the injury happened near the bone-cartilage interface, injuring both.

It certainly sounds as if this might be worse than an oblique injury, but is it?

We know oblique injuries in position players result in an average stay of 26.7 days on the disabled list, based on a study published in the American Journal of Sports Medicine in 2012. In that study, nearly three-fourths of the injuries to position players occurred on the opposite side of (contralateral to) their dominant batting side. These injuries are clearly not quick to heal and complicating matters, there is a reinjury rate of approximately 12 percent. Part of the challenge in recovery is that soft tissue healing is easily disrupted by too much tension (stretching) or by too aggressive shortening (via muscle contraction).

Bone is typically more predictable in its healing. Avulsion fractures, which are more common in the ankle or foot, often heal without surgical intervention. Treatment initially often consists of rest while allowing pain and inflammation to subside. Subsequent treatment often follows the path of what the local soft tissue would indicate. In McCutchen’s case, this would suggest that after a period of rest, he will gradually incorporate a rehab strategy similar to that for an oblique strain, progressing as his symptoms allow.

By not immediately placing him on the DL, the Pirates clearly hope that McCutchen’s injury will progress more quickly than a standard oblique injury. Unfortunately, there are virtually zero comparisons to apply. I conducted an informal poll of several medical professionals who have cared for elite baseball players for years. When asked how many avulsion fractures of this type they had ever seen, the response was universal: none.

The mechanism of McCutchen’s injury (a hard swing) and the location of his pain (contralateral lower rib cage) are typical of oblique injuries in position players, which explains why this was presumed initially by many to be the diagnosis. It would seem since the presentation has so many similarities to an oblique strain, the safest assumption would be that it will behave similarly to an oblique in its healing pattern. If that is indeed the case, McCutchen would likely miss in the neighborhood of three to four weeks.

The Pirates, however, are hoping for a different outcome. Perhaps McCutchen’s signature speed will carry over to his recovery, teaching us that avulsion fractures at the 11th rib result in a quicker return to play.