On Wednesday, Opening Day Eve, the Royals got some pretty crushing news. All-Star catcher Salvador Perez tore his MCL while carrying luggage up some stairs and will be missing 4-6 weeks. The injury doesn't look to require surgery, but losing a player the caliber of Perez for over a month of the season is a big blow to any team. 

Further, sometimes injuries continue to affect players -- now in terms of performance -- once they are able to return to the field. What can we expect when it comes to Sal and his MCL? I turned to a knee expert: Orthopedic surgeon Dr. Rodney Benner of the Shelbourne Knee Center in Indianapolis. 

Let's hit this Q&A style. 

Matt Snyder: It's a torn MCL for Salvador Perez. The Royals say he's out 4-6 weeks. Generally speaking, do you think that kind of timetable is accurate?

Dr. Rodney Benner: Recovery from a torn medial collateral ligament (MCL) can vary from as little as a week or two, to as many as eight weeks, depending on how bad the tear is, with grades 1-3. It has been reported that this tear is a grade 2 injury, which is usually a 4-6 week recovery.

Snyder: What about Perez being a good defensive catcher? Does an injury like this continue to be an issue even after he returns to the field?

Dr. Benner: Catchers are prone to knee injuries with all of the squatting and standing that they do playing defense. However, while this does put significant stress on the medial meniscus, the cartilage on the inside of the knee, catching doesn't generally cause MCL injuries, and as such, an healed MCL injury shouldn't hinder Perez from continuing to be a standout defensive catcher in the future.

Snyder: What is the role of the MCL in the knee and how is it tested in baseball, whether as a catcher, hitter or baserunner? What will be the hardest thing to do for Perez when he starts working back into shape?

Dr. Benner: The MCL is the main stabilizing ligament in the medial (inside) side of the knee. It provides resistance to valgus stress, which happens when the foot is planted and a force contacts the outside of the knee. This pull the two bones apart on the inside and the MCL resists this displacement. However, if the stress is forceful enough, the ligament tears.

This type of injury is not a common one on baseball. It is much more common in contact sports, such as football. The main limitation is instability in the immediate term, as the tear causes the knee to feel unstable, particularly with side-to-side movement. One place this is particularly vulnerable is during the swing. As the batter twists on the back leg, it can stress the ligament, and as such, this motion can be painful. However, in Perez's case, the injury is in the left knee, which is preferable in a right handed hitter.

Once the unstable feeling improves as the ligament heals, the main limitation becomes pain and stiffness, rather than instability. Rehabilitation focuses on the return of range of motion and strength, followed by a functional progression of increasing sport-specific activity.

Snyder: So far, Royals manager Ned Yost said he doesn't think surgery will be necessary on Perez's tear. What would go into the decision-making process on whether or not to have surgery on a torn MCL? Is either way more risky for a re-injury?

Dr. Benner: Isolated MCL injuries reliably heal without surgery.  At times, if other ligaments, such as the ACL or PCL or both are torn, surgery can become an option. By this point, Perez has undoubtedly been examined by either an athletic trainer or orthopaedic surgeon, as well as having an MRI scan, thus ruling out injury to other ligaments.

There you have it. In all, I'd say this sounds like pretty good news -- obviously balancing against the backdrop of the awful news from Wednesday night -- for Royals fans and people worried about Perez's status for fantasy baseball. Wait out the 4-6 weeks, then he'll be same ol' Sal. It certainly could have been much worse. Also, he's such an ironman, don't be surprised if he heals quicker than expected.