Baseball

James R. Andrews

Christopher G. Mazoue

INTRODUCTION

Baseball pitching is one of the most demanding motions on the shoulder in sports. Each pitch requires the generation of tremendous forces and torques on the shoulder to create the acceleration necessary to propel a baseball at high velocities, then decelerate the upper extremity after the ball has been released. Each baseball pitch can result in humeral angular velocities of 7,000 to 8,000 degrees per second making it one of the fastest movements in sports (1,2). For this energy to be produced during a pitch, the shoulder must allow for extremes in range of motion and flexibility, yet must provide a certain level of stability in a joint that has little inherent stability. Thus, the shoulder must maintain a delicate balance of mobility and stability while generating levels of energy via muscular contractions that are believed to be near physiologic limits for each of the hundreds or thousands of pitches that may be thrown over the course of each year. The dynamic and static tissues of the shoulder that provide this balance and energy generation are highly susceptible to overuse injuries in the context of the demands that are placed upon them.

With the large numbers of individuals of all ages participating in baseball, injuries to the shoulder are commonplace. An extensive amount of both biomechanical and clinical research has been focused on the baseball player in order to greater understand the kinetics and kinematics of the baseball pitch and the pathophysiology of the shoulder in the baseball player. This chapter concentrates on our experience with the throwing shoulder in the baseball player and our approaches to the diagnosis, nonoperative treatment, surgical techniques, and rehabilitation protocols for baseball players.

PITCHING MECHANICS

To understand the pathophysiology of the throwing shoulder in the baseball player, it is helpful to have a basic knowledge of the mechanics of the baseball pitch. Based on analyses of hundreds of baseball pitchers using high-speed video and computerized motion analysis at the American Sports Medicine Institute (ASMI), we have divided the baseball pitch into six phases (Fig. 21-1): wind-up, stride, arm cocking, arm acceleration, arm deceleration, and follow-through (1).

The wind-up phase starts from a two-legged stance. The pitcher brings the front leg to a tucked position, preparing the body for the remainder of the pitch sequence. This phase ends when the ball is removed from the glove. There is no excessive strain placed upon the pitcher’s shoulder and electromyographic (EMG) analysis has revealed little muscular activity across the shoulder during this phase (3, 4, 5, 6, 7, 8, 9, 10).

Strideis defined as the sequence of activities from the end of the wind-up phase until the front foot strikes the ground. During this maneuver, the body is advanced forward; however, the hand and ball remain positioned behind the body. This places an eccentric load on the humeral adductors and internal rotators, effectively creating a preload on these muscles as they prepare to accelerate the shoulder.

The sequence from foot contact until achievement of maximal external rotation of the throwing shoulder is defined as the arm cocking phase. During this phase, shoulder external rotation can reach 165 to 180 degrees and an anterior translation force of approximately 50% body weight is generated (1,11,12). Significant stresses are placed on the anterior capsule and soft tissues of the shoulder during this phase, especially at the anterior band of the inferior glenohumeral ligament. As the shoulder is repetitively placed in this position of maximal external rotation, attenuation of these anterior static restraints may occur through repetitive microtrauma (13). This, in turn, may lead to pathologic laxity of the anterior ligaments and capsule, producing occult instability or microinstability of the shoulder (13). The rotator cuff muscles, as dynamic stabilizers of the shoulder, must therefore work to prevent abnormal anterior translation of the shoulder in this position. This predisposes these muscles to overuse injuries.

From the position of maximal external rotation of the throwing shoulder until ball release is the arm acceleration
phase. Within approximately 0.05 to 0.08 second, the baseball is accelerated forward from a stationary position to speeds in excess of 80 mph in high-level athletes (12). The rotator cuff and scapular stabilizing muscles all demonstrate high levels of activity during this phase (3, 4, 5, 6, 7, 8, 9, 10).

FIGURE 21-1. The six phases of pitching: wind-up (A-C), stride (C-F), arm cocking (F-H), arm deceleration (I-J) and follow-through (J-K). (From Dillman CJ, Fleisig GS, Andrews JR. Biomechanics of pitching with emphasis upon shoulder kinematics. J Orthop Sports Phys Ther 1993;18:402, with permission.)

The arm deceleration phase progresses from ball release until maximal shoulder internal rotation. Large shoulder forces and torques are required to decelerate the upper extremity and counteract the anterior distraction forces on the shoulder joint, which may approach body weight (12). This phase is the most violent phase on the shoulder. The rotator cuff must both decelerate the shoulder via large eccentric contractions and stabilize the shoulder against anterior translation. Any underlying anterior instability of the shoulder requires even greater activity of these dynamic stabilizers. These large, repetitive loads on the rotator cuff during deceleration may result in tension injuries. In addition, large tensile loads are applied to the posterior capsule during deceleration, which may lead to chronic attenuation of the posterior capsule and posterior laxity.

The final phase is the follow-through. Posterior shoulder muscles continue to eccentrically contract during this phase. This phase is important for final dissipation of the energy generated during the throwing motion.

PATHOPHYSIOLOGY OF PITCHING

The activity of the scapula and its stabilizing muscles and the coordination of scapular function during the pitch cannot be overemphasized. The scapula functions as a mobile base for the shoulder. The movement of the scapula allows maintenance of proper length-tension relationships for the deltoid and rotator cuff muscles (14). Failure of coordinated scapular movements can increase both tensile and compressive stresses on the rotator cuff, increasing the possibility
of failure of these structures. Diminished EMG activities of the scapular stabilizing muscles during the pitch in patients with glenohumeral instability supports the role that these muscles play in creating a stable base for overhead activities (4).

Although we have concentrated on the shoulder, we cannot forget that the baseball pitch requires a coordinated transfer of energy from the legs and pelvis, trunk, shoulder, upper arm, forearm, and finally the hand as the ball is delivered. The sequential transfer of energy from the legs and pelvis to the hand is defined as the kinetic chain (14). Any loss of energy or coordination from this chain can lead to failure or fatigue of the remainder of the chain, leading to injury.

The severe stresses placed upon the shoulder during the throwing motion can lead to developmental changes in the function and anatomy of the shoulder. In most mature baseball pitchers, there is an increased external rotation and decreased internal rotation of the throwing shoulder in abduction as compared with those of the nonthrowing shoulder (1,15,16). The total arc of motion of the throwing shoulder is, therefore, not increased, but simply moved posteriorly. It has been postulated that this shift in rotation of the shoulder is secondary to increases in anterior capsular laxity and posterior capsular tightness in the overhead athlete (17). More recent literature proposes an alternative theory behind this rotational shift in the arc of motion in baseball players. This theory suggests that the dominant humeral head in the young overhead athlete undergoes an osseous adaptation secondary to the stresses placed on the immature proximal humerus during the throwing motion. This osseous adaptation produces increased retroversion of the dominant shoulder, which, in turn, results in decreased internal rotation and increased external rotation (18, 19, 20). In a recent study looking at professional baseball pitchers, the dominant shoulder was found to have 17 degrees more humeral head retroversion and 3 degrees more glenoid retroversion than the nondominant shoulder (18). This same study compared range of motions of the dominant shoulder compared with those of the nondominant shoulder, with the dominant shoulder exhibiting 9 degrees more external rotation and 9 degrees less internal rotation than the nondominant shoulder. Therefore, as previously discussed, the total arc of motion (189 degrees) was the same for both shoulders in the throwing athlete with the arc of motion rotated posteriorly in the dominant shoulder. These findings again illustrate how significant the stresses are to the shoulder in throwing athletes and how the body adapts to offset these stresses.

HISTORY AND PHYSICAL EXAMINATION

A thorough history is invaluable in the diagnosis of throwing injuries in baseball players. Because most injuries in overhead athletes are secondary to overuse and fatigue, it is crucial to gain an understanding of the onset of symptoms and a detailed history of the throwing activities since the onset of symptoms. Table 21-1 (21) provides a baseline for establishing a thorough history in baseball players with shoulder pain. Table 21-2 (21) provides a guideline for the physical examination. The physical examination is used to further localize the possible site of injury that is suspected based on the history. It is imperative for an examiner to become familiar with a consistent routine to evaluate the thrower’s shoulder. Although the examination is used to correlate a patient’s symptoms with anatomic pathology, all possible sources of injury should be evaluated in each shoulder. Of particular importance in throwing athletes, especially
with regard to range of motion and stability, is examination of both the dominant and nondominant shoulders.

TABLE 21-1. HISTORY IN THE THROWING SHOULDER

I.	General information
	Age
	Gender
	Dominant handedness
	Position
	Years throwing
	Level of competition
II.	Injury pattern
	Onset of symptoms—acute or chronic
	History of trauma or sudden injury
III.	Symptom characteristics
	Location of symptoms—anterior, lateral, posterior
	Quality of symptoms—sharp, dull, burning
	Presence of mechanical symptoms
	Presence of weakness or instability
	Severity of symptoms
	Duration of symptoms
	Activities that worsen symptoms
	Activities that relieve symptoms
	Duration of symptoms
	Presence of neurosensory changes
	Phase of throwing-producing symptoms
	Type of pitch-producing symptoms
	Innings pitched in season/year
	Frequency of starts/relief appearances
	Change in velocity of pitches
	Loss of control/location of pitches
IV.	Treatment/rehabilitation
	Amount of rest from throwing
	Type and duration of rehabilitation
	Type, location, frequency of injections
V.	Related symptoms
	Neck pain
	Radicular symptoms
	Brachial plexus injury
	Peripheral nerve entrapment
VI.	Medical information
	Past medical/surgical history
	Medications
	Allergies
	Family/social history
	Review of symptoms

TABLE 21-2. PHYSICAL EXAM IN THE THROWING SHOULDER

SITTING POSITION
I.	Inspection
II.	Palpation
	Sternoclavicular joint
	Acromioclavicular joint
	Clavicle, acromion, coracoid
	Bicipital groove
	Scapula
	Musculature
III.	Range of motion
	Crepitus
	Glenohumeral motion
	Scapulothoracic motion
IV.	Motor strength
	Rotator cuff
	Scapular winging
V.	Impingement signs
	Neer/Hawkins signs
	Cross chest adduction test
VI.	Stability tests
	Anterior, posterior, inferior stability
VII.	Special tests—biceps
	Speed’s test
	Yergason’s test
VIII.	Special tests—SLAP
	O’Brien’s test
	Crank test
	Lemak test
	Mimori test
IX.	Neurologic examination
X.	Cervical examination
SUPINE POSITION
I.	Range of motion
II.	Anterior instability tests
	Anterior drawer
	Apprehension test
	Relocation test
III.	Posterior instability test
	Posterior drawer
	Apprehension test
IV.	SLAP test
	Clunk test
V.	Internal impingement test
PRONE POSITION
I.	Palpation posterior shoulder
II.	Stability test
	Anterior apprehension

For every overhead athlete, we obtain a standard “thrower’s series” of radiographs, which includes true anteroposterior views with the arm in maximum internal rotation and external rotation, a modified Stryker’s notch view, and an axillary lateral view. A scapular outlet view may be obtained when external impingement is suspected. When magnetic resonance imaging (MRI) is required, we prefer MR arthrography following intraarticular saline injections. This technique greatly enhances visualization of the glenoid labrum and subtle rotator cuff tears.

The ultimate diagnosis of shoulder injuries in baseball players can be difficult. The soft tissues of the shoulder are subjected to tremendous stresses from throwing a baseball that result in overuse injuries. Partial thickness rotator cuff tears and labral tears are common findings on MRI in baseball players. Yet, not all of these rotator cuff and labral tears are symptomatic. It is the job of the examiner to determine whether radiographic findings correlate with the patient’s symptoms and physical examination. This can be challenging.

REHABILITATION

Because most shoulder injuries in baseball players are secondary to overuse and fatigue, most of these injuries can be treated with initial active rest, followed by a strict supervised physical therapy program. Active rest involves the athlete participating in activities that do not require throwing a baseball or engaging in other overhead activities. Based on the patient’s symptoms and suspected diagnosis, we often rest a player for 6 to 12 weeks. During this time, we start a supervised physical therapy program. This program must focus on strengthening the rotator cuff muscles as the dynamic stabilizers of the glenohumeral joint and improving coordination of the rotator cuff and scapular stabilizing muscles. We teach our overhead athletes a program called the “thrower’s 10” (Chapter 7), which consists of 10 exercises for the muscles of the shoulder and scapula that were developed on the basis of the contribution of these various muscles during the throwing motion as determined by EMG (22, 23, 24). These exercises can be used as a rehabilitation tool or as a group of core exercises to be used for maintenance throughout the year. Following progression through the thrower’s 10 program, we encourage use of plyometric exercises. These are movements that focus on eccentric muscular contractions before concentric contractions. These exercises enhance strength and dynamic stability of the shoulder and are excellent transitional exercise before throwing activities are resumed. When the athlete is ready to resume throwing, following the appropriate period of active rest and initial physical therapy, an interval throwing program is begun. The baseball player must be monitored throughout this interval throwing program and must be patient with its progression. If an individual progresses through the entire throwing program without symptoms, then the athlete is cleared for competitive activities.

For hitters, we have developed an interval hitting program to ease the baseball player back into full swings (Table 21-3). We often initiate this program before beginning the interval throwing program following a surgical procedure to the shoulder.

In most cases of shoulder injuries in baseball players, we do not consider surgical intervention until the athlete has
failed a prescribed, supervised shoulder rehabilitation program after 3 months. Most baseball players do well with nonoperative treatment.

TABLE 21-3. INTERVAL HITTING PROGRAM

Off a tee stand
	Step 1: 50% effort (15-20 swings)
	Step 2: 50% effort (2 sets of 15 swings)
	Step 3: 65%-70% effort (2 sets of 15 swings)
	Step 4: 70%-75% effort (2 sets of 20-25 swings)
	Step 5: 80%-90% effort (2 sets of 25 swings)
Soft toss swings: Warm-up using a tee stand
	Step 6: 50%-60% effort (15-20 swings)
	Step 7: 65%-70% effort (2 sets of 20-25 swings)
	Step 8: 80%-90% effort (2 sets of 25 swings)
Batting practice swings: Warm-up with soft toss swings
	Step 9: 50%-65% effort (2 sets of 25 swings)
	Step 10: 70%-75% effort (2 sets of 30 swings)
	Step 11: 80%-90% effort (2 sets of 30-35 swings)
	Hit 3 times per week with a day off in between.
	Perform each step for 2 days before progressing to next step.