America’s pastime is one of the most popular sports played today. It has been estimated that more than 8.6 million children ages 6-17 are involved in youth baseball in the United States (16).

Although classified as a “limited contact” sport, the incidence of injury ranges between 2% and 8% of participants per year (12).

Serious injuries are associated with blunt chest impact and head and eye trauma.

Most injuries involve soft tissue trauma or throwing injuries.

Biomechanics of overhand throwing depends on adequate transfer of momentum. This kinetic energy is produced from larger slower muscles and transferred to smaller faster body parts (9).

Anatomy of the shoulder includes the sternoclavicular joint, acromioclavicular joint, glenohumeral joint, and scapulothoracic joint. The glenohumeral joint is a complex joint involving many static stabilizers including the joint capsule, glenoid labrum, glenohumeral ligaments, and dynamic stabilizers including the rotator cuff musculature.

Anatomy of the elbow includes the ulnotrochlear joint, radiocapitellar joint, and proximal radioulnar joint. Further stabilizers include the medial and lateral collateral ligament complexes. Musculature of the elbow includes the biceps brachii, brachioradialis, brachialis, triceps, anconeus, supinator, and pronator teres.

Ossification of the pediatric elbow is important to understand, because age can help determine the injury pattern. Ligaments are stronger than the physis, and therefore, the injury is more likely to involve the bone than the soft tissue. The distal humerus has four ossification centers; the radius and ulna each have one. The capitellum is the first to ossify, followed by the radius, the medial epicondyle, the trochlea, the olecranon, and finally the lateral epicondyle.

Six phases of throwing: (1) Windup begins with initial movement of the pitcher, the deltoid abducts the arm, and ends when the hands come apart or ball leaves the nondominant hand. (2) Early cocking begins when the hands come apart, the deltoid abducts the arm, the infraspinatus and teres minor externally rotate the shoulder, and ends when the front leg is extended and strikes the ground. (3) Late cocking begins when the front foot strikes the ground, the glenohumeral joint externally rotates, and ends when the shoulder is maximally externally rotated. (4) Acceleration begins with the ball moving forward, horizontal adduction and internal rotation of shoulder, and ends when ball is released. (5) Deceleration occurs after the ball is released. (6) Follow-through ends when motion stops.

Pitchers develop a shift in the rotational arc of motion of the shoulder, with an increase in external rotation and a compensatory decrease in internal rotation.

Deliveries include overhead, three-quarters, and sidearm, each with their own specific risks of injury.

Rotator cuff injuries vary from mild forms of tendonitis and impingement to complete tears. They are often due to overuse injuries and can be associated with joint instability. Examination findings include a positive Neer’s sign, positive Hawkin’s sign, and pain and weakness with resistive muscle testing. If a tear is suspected, the rotator cuff can be visualized on magnetic resonance imaging (MRI). Treatment varies from nonsteroidal anti-inflammatory drugs (NSAIDs) and physical therapy to surgery, depending on the severity of the injury.

Instability can be due to labral injury, trauma, poor mechanics, overuse, or generalized joint laxity. Symptoms include pain during the acceleration phase of throwing. Physical examination findings include a positive apprehension and relocation test, a positive load-and-shift test, and possibly generalized ligamentous laxity. MRI or MRA is the diagnostic modality of choice to evaluate the status of the glenoid labrum. Treatment includes physical therapy with scapular stabilization exercises and, if severe or unresponsive to conservative treatment, may include surgical repair.

Superior labral injuries may occur due to trauma, instability, poor mechanics, or changes in throwing or training. Symptoms include painful clicking, pain with overhead actions, and
pain with acceleration. SLAP lesions (superior labrum anterior posterior) are common in throwers. Internal impingement is found primarily in pitchers. It occurs during the cocking phase and is caused by repetitive contact between the undersurface of the rotator cuff insertion on the greater tuberosity and the posterosuperior glenoid with abduction and external rotation of the shoulder during the cocking phase of throwing. Examination findings include a positive clunk test, a positive grind test, and a positive O’Brien’s test. MRI is the diagnostic modality of choice to evaluate the status of the superior labrum. Conservative treatment includes physical therapy, rest, and NSAIDs. For internal impingement, stretching of the posterior structures is advised. Treatment is surgery if conservative therapies fail.

Bennett lesion is a region of mineralization at the posterior-inferior glenoid rim. This ossification is unique in throwing athletes and is often associated with rotator cuff injuries or instability. Symptoms are usually related to secondary shoulder pathology, and diagnosis is made with a computed tomography (CT) scan. Conservative treatment is favored over surgical intervention (3).

Osteochondritis dissecans

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