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Michael Wacha's injury is why the Cardinals needed to add pitching

An in-depth look at what's wrong with Michael Wacha, and what it's going to take to get him pitching again.

Jeff Curry-USA TODAY Sports

The St. Louis Cardinals thought they were deep in starting pitchers before the season started, yet they made a pair of daring trades at the deadline for two starting pitchers. An injury to Michael Wacha changed everything.

Wacha was one of the surprises of the 2013 season, allowing a 2.18 ERA in September and October as the St. Louis Cardinals made their second World Series appearance in three years. This season, Wacha held opponents to a 2.79 ERA in 15 starts before landing on the disabled list. However, he landed on the disabled list soon after with a stress fracture in his right scapula, or shoulder blade.

The scapula and all 17 of the muscles that attach to it are an integral part of proper shoulder function. When moving the arm overhead, the scapula comprises roughly one-third of the total shoulder motion. For proper overhead motion, the scapula needs to turn outward while staying flush to the body. Any deviations can put excess stress on another part of the shoulder or arm.

The rotator cuff is also an important component of shoulder structure, movement, and function. Comprised of four muscles -- subscapularis, supraspinatus, infraspinatus, and teres minor -- the cuff provides stability to the shoulder joint during movement. Healthy rotator cuff muscles will activate with every shoulder motion to keep the head of the humerus within the shoulder joint capsule.

In addition to stability, the rotator cuff is also an important component of the pitching motion. The muscles of the cuff are responsible for decelerating the arm at the end of the motion. Considering how rapidly a pitcher like Wacha needs to move his arm in order to throw a baseball 90 miles per hour or faster, it's easy to understand why the deceleration of this motion puts so much stress on the cuff.

In Wacha's case, the rotator cuff muscles are likely to blame, despite not being the site of the injury. Wacha's stress fracture, believed to be similar in nature to the one Brandon McCarthy suffered earlier in his career, is the result of the rotator cuff muscles repeatedly pulling at the outside border of the scapula. The repeated pulling can cause irritation and pain in the muscle and tendon. If left untreated long enough, that continued pulling can cause irritation in the bone, or a stress reaction. If the issue is not resolved, the bone can eventually become brittle enough to break apart. Children and young teens may see the bone split into two pieces, which is called an avulsion fracture. Older teens and adults often do not get a clean break; rather, the bone splits into multiple tiny pieces, small enough to go undetected by an x-ray. This is a stress fracture.

Unfortunately, stress fractures do not heal as quickly as a normal fractured bone. In order to allow a stress fracture to heal, the "stressful" motion needs to be stopped. While this seems simple in Wacha's case, it can be a longer process than many realize. Considering how active the rotator cuff is with any and all shoulder movements, even a simple motion like lifting the arm overhead could continue to impact the injured area. After getting any resting pain and inflammation under control, the healing process takes six to eight weeks.

While stress fractures are often a result of overuse, there can also be an underlying impairment that puts a person at greater risk for developing inflammation. In runners who develop shin splints, foot position and arch support can play a big role in gait mechanics.  We may see the Cardinals tinker with Wacha's mechanics once he starts to throw again. Wacha's shoulder motion and joint mobility are also factors that will need to be addressed during his rehab. The Cardinals will be patient, but considering their busy deadline, they will also be pragmatic.