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Causes and Mechanisms of Shoulder Throwing Injuries

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Physiotherapy in Calgary for Baseball

Shoulder problems in the throwing athlete are common but very complex. It can be a real challenge to identify the specific cause of the problem and treat it quickly and easily. Many throwing athletes don't allow enough time to rest the shoulder between games and especially after an injury. The authors of this article provide a review of the causes and mechanisms of shoulder throwing injuries. They describe how the anatomy of the shoulder changes with repetitive throwing. And they offer suggestions for a successful rehab program.

Over time and with much study, researchers are slowly coming to understand more and more about how the shoulder works and what shifts occur in muscle balance, motor control, and kinematics (movement) in the throwing athlete. Muscle fatigue, stretching out (laxity) of the shoulder capsule, and torsion or a slight twist of the humerus (upper arm bone) are examples of ways the shoulder complex can change with repeated throwing motions, thus leading to shoulder problems. Even the smallest damage to the soft tissues, joint surface, or bone can set up a chain of events that result in shoulder injuries.

The sequence of movements required in throwing sports when repeated over and over can cause microtrauma that eventually leads to break down of the tissues. There is a delicate balance of mobility and stability required with every high-speed pitch. Movement scientists are still unraveling the complexities of throwing mechanics and what contributes to injury. Understanding the way the shoulder and body move during throwing activities is helpful for the physiotherapist who is guiding the athlete through recovery during the rehabilitation process.

The authors review (in detail) the kinematics of throwing. They provide drawings and descriptions of the six phases of throwing from wind-up to delivery. With pitches at 90 miles per hour or more, the entire pitch sequence can take less than five seconds. Acceleration and deceleration forces along with compressive, shear, and distractive forces of repetitive high-speed pitches can put the shoulder at risk for injury.

In order to deliver the pitch precisely where the pitcher wants it to go, specific arm motion and positions must accompany the exact timing of ball release. And the successful pitcher must be able to do this over and over with speed and accuracy. Sometimes those requirements exceed the fatigue strength of the muscles and other soft tissues around the shoulder.

New understanding of the role of the scapula (shoulder blade) has also changed how we view throwing injuries. Now we know that scapular dynamics are extremely important. It's not just the arm and shoulder that are involved in a pitch. Half of the energy that goes behind a pitch comes from the legs and trunk. Rotational forces needed for the forward delivery of the pitch are transferred from the lower body to the shoulder through the scapulothoracic joint. The scapulothoracic joint refers to where the scapula moves over the rib cage.

Injury prevention has improved tremendously as a result of motion studies of throwing actions. Being able to see (and analyze) movements in slow motion has expanded the understanding of normal and abnormal shoulder function during throwing activities. This information has helped shape today's injury prevention and rehab programs.

Physiotherapy for injuries such as shoulder laxity and instability, impingement, and tendon or ligament tears is broken down into four phases. The first phase takes place when the injury is new or fresh. This is called the acute phase. The therapist helps the athlete understand the importance of activity modification and giving the injured tissues a chance to heal. Various treatment methods such as neuromuscular facilitation, lymphatic drainage, and rhythmic stabilization exercises are used by the therapist to help promote healing.

Phase two begins when the pain and inflammation of the acute phase have decreased. In this phase, the therapist uses specific exercises to strengthen and re-tune the muscles. Other exercises are used when there's too much motion or not enough motion in any part of the arc of shoulder movement. The therapist must carefully examine each throwing athlete to identify exactly which soft tissues are affected, why, and what to do about it.

When tests show that the athlete's shoulder is stable with only a mild loss of motion and no pain, then the program can be stepped up to the third phase. Here the training becomes more intensive with endurance drills, plyometric training for speed, and an interval throwing program. Interval throwing progresses pitches through various distances, speeds, and intensities on and off the baseball mound with plenty of rest periods in between. The player is taught how to regain speed without overtraining before moving to the final phase.

Phase four continues to advance the pitcher through a series of advanced interval throwing exercises, strengthening and conditioning exercises, and a maintenance program at the pre-injury level of performance and play. If all goes well, the athlete is returned to the game. If there has been no improvement (or not enough improvement), then additional testing and possibly surgery may be advised.

The authors provide therapists with additional information in how to apply this four-phase rehab program to players with specific problems that do require surgical repair such as a superior labrum anterior-posterior (SLAP) injuries or rotator cuff tears. SLAP lesions affect the labrum and biceps tendon where it attaches to the labrum. The labrum is a fibrous rim of cartilage around the rim of the shoulder socket. It helps hold the shoulder in place. Forces powerful enough to injure the labrum can be very disabling to the throwing athlete.

After surgery, the patient is guided through all four phases of rehab. Phase one is used when the surgical repair needs to be protected. The progression from phase one through phase four depends on the type of injury and type of repair. Minor surgical repairs such as debridement (shaving frayed edges of the labrum) can be progressed fairly quickly with little down time (immobilization). Players with severe full-thickness rotator cuff tears may not be able to return to a preinjury level of play. With all injuries, the therapist must assess scapular motion and provide rehab to restore normal kinetic motion when needed.

Scapular dyskinesia (loss of normal scapular motion) is a fairly new diagnosis. We know it is caused by muscular imbalances, trauma, or nerve injury. But what to do about it and how to treat it effectively are still being studied by physiotherapists. Without a strong, normally functioning scapula, pitchers and other throwing athletes may end up compensating with other muscles and other shoulder motions. Such compensatory actions can also lead to increased load on the shoulder and yet another injury. The therapist includes exercises to strengthen and condition scapular muscles. Surgery is rarely needed for scapular dyskinesia.

The authors conclude by saying that many (if not most) shoulder injuries in throwing athletes can be successfully treated conservatively. Physiotherapy to restore normal range and coordination of movement is the basis for regaining smooth kinetic motion. A program of specific exercises is often the answer to get the entire shoulder complex to a place where it can handle the demands of repetitive throwing in competitive sports. Shoulder conditioning (including adequate rest and recovery) is the key to preventing injuries in the first place.

Reference: Sepp Braun, MD, et al.Shoulder Injuries in the Throwing Athlete. In The Journal of Bone and Joint Surgery. April 2009. Vol. 91. No. 4. Pp. 966-978.

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