Darwin Barney, CHN (Left knee PCL sprain)
Headfirst slides are more dangerous than feetfirst slides, especially at home plate, but they are necessary at times in order to avoid a tag. As Barney slid headfirst to score the winning run on Monday night, he landed on his left knee and tried to push off it at the same time to avoid a tag. While he was successful in scoring the run, he also felt his leg go numb.

Barney finished the game, but he woke up the next day with a very sore knee. After consulting with the Cubs’ medical staff, he was sent for an MRI, which confirmed the Grade I posterior cruciate ligament (PCL) injury. Barney was subsequently placed on the 15-day disabled list.

Unlike the dreaded ACL injury, isolated PCL injuries in adults usually do not require surgery to maintain stability in the knee. Despite the close proximity of the ACL and the PCL inside the knee joint, their roles are vastly different in relation to the stability of the knee. The ACL is responsible for a very large percentage of its stability, while the PCL plays a much smaller role. In fact, roughly 15-20 NFL players suffer PCL injuries each year, and rarely has surgery been necessary unless other structures have been involved.

The anatomy of the knee—and more specifically, the PCL—explains why athletes can opt to go through rehabilitation rather than undergoing reconstruction after injuring the PCL. To begin with, the PCL is stronger and thicker than the ACL, which translates to fewer injuries. The PCL runs from near the front toward the back inside the knee joint, exits the joint itself, and then attaches about half an inch down the back of the tibia. This is important because depending on where the tear occurs, the ligament can heal or tighten itself, unlike the ACL.

One other reason why isolated PCL injuries require surgery less often than ACL injuries is the relationship of the muscles acting on the knee. The two major muscle groups involved are the hamstrings and the quadriceps. The hamstring helps to protect the ACL from detrimental forces acting on the tibia, while the quadriceps help to protect the PCL. The quadriceps are much more powerful than the hamstrings and can rebuild strength more easily after injury, making it easier to protect the PCL than the ACL.

Strengthening the hamstring can be difficult, and its role in protecting the ACL is one of the reasons why sports medicine professionals say you can never strengthen the hamstrings enough. It's also one of the major reasons why ACL prevention programs—at least good ones—emphasize hamstring strength along with other exercises and techniques. Strengthening the quadriceps is much easier and can be done with many different exercises, all of which protect the PCL.

The PCL provides almost all of the resistance to backward (posterior) movement of the tibia (shin) on the femur (thigh). Isolated injuries to the PCL most often result from a direct posterior force on the tibia, such as falling directly on a bent knee or a motor vehicle accident in which the knee strikes the dashboard. These forces drive the tibia backward and lead to tearing of the PCL.

The PCL isn't always injured in isolation; it can also be injured in combination with fractures of the tibia or other various soft tissue structures, resulting in multi-plane instability. Surgery becomes necessary when multi-plane instability is present, in order to improve the function of the knee as well as to protect its long-term health.

If surgery is not performed, time is taken to allow the PCL to scar in and try to heal itself. Exercises are performed to ensure full range of motion and rebuild quadriceps strength, and returning in a brace for a period of time is a possibility. With proper rehabilitation, there is not much risk for further injury, although the biggest long-term risk of isolated PCL injuries is patellofemoral (kneecap) arthritis.

Barney's injury did not appear to be very severe, and the MRI confirmed the Grade I sprain. Players in non-collision sports can often return from Grade I PCL sprains in about three weeks, once the ligament has tightened back up and the swelling subsides. Barney should not have much difficulty in his return, although he’ll have to watch out for players sliding into his leg at second base.

Allen Craig, STL (Right patellar fracture)
In Monday's edition of Collateral Damage, we discussed the different types of diagnostic tests and their uses. Little did we know that we would be able to point to another illustration of the differences between them so soon.

Craig was place on the disabled list after running into the wall and suffered what was thought at the time to be a contusion of his patella. His pain and swelling were more than a little suspicious, so further testing was performed, and it revealed the small fracture. (From here on out, assume that any disabled list transaction for a bony contusion may also involve a minor fracture.) These small fractures take about three to six weeks to heal, putting Craig out until around the All-Star Break.

Brandon Lyon, HOU (Right biceps tendinitis)
Lyon is back on the disabled list, and there is growing concern that he will need surgery on his troublesome shoulder. He just came off a DL stint for a partially torn rotator cuff and inflammation surrounding his biceps tendon, and to return to it so quickly is certainly not a good sign.

The shoulder is a unique joint that relies on its muscles for everything from movement to stability. If the rotator cuff is not functioning properly, other structures will become compromised or inflamed. This will in turn lead to further injury to the rotator cuff, and the cycle continues until major structures are completely torn. Lyon will visit Dr. Yocum today, and a determination about a course of action will be made. Surgery is definitely not off the table, since he has failed physical therapy and has a known partial rotator cuff tear.

Eduardo Sanchez, STL (Right shoulder strain)
Sanchez returned to St. Louis to have his shoulder examined after experiencing some tightness in his right shoulder and a sudden, unexplained drop in velocity. This isn’t the first time he has been knocked out of action by a shoulder injury: he also missed the last few weeks of the 2008 season while in the minors. After further examination yesterday, Sanchez was placed on the 15-day disabled list, though the Cardinals insist that it’s just a precautionary move.

Flesh Wounds: Alfredo Simon joined some Orioles teammates on the 15-day DL with a strained right hamstring… Edward Mujica sprained his right wrist in a collision at first base. He's day-to-day for now… Jeremy Guthrie will have an MRI today for a strained upper back muscle… Joe Mauer was finally activated yesterday… Clay Buchholz left his start early because of a blister. He has been battling the blister and back problems for a few weeks now… Chipper Jones was pulled from yesterday's game early with a strained right groin. One more and he reaches entry number 80 in the database.

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Corey/Ben - what's your take on Tommy Hanson's diagnosis?
Seems to be fairly straightforward with it but a little concerned given his upper back/shoulder soreness in spring training. Given where we are in the season they probably should put him on the DL just to calm everything down and bring him back in the minimum. This way they can enjoy his productivity down the stretch.
What are your thoughts on Jed Lowrie? His shoulder injury has been nagging him, and he had to leave last night's game after his first AB.
Going to talk about that some more on Monday
How long will Tommy Hanson and Shaun Marcum be out? I really think this series should have daily update.