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Injury Prevention for Throwing Athletes Part I: Baseball Bat Training to Enhance Medial Elbow Dynamic Stability

Crotin, Ryan L. MA, CSCS; Ramsey, Dan K. PhD

Strength and Conditioning Journal: April 2012 - Volume 34 - Issue 2 - p 79–85
doi: 10.1519/SSC.0b013e31824f6e5d
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SUMMARY BASEBALL PITCHERS' ELBOWS ARE EXPOSED TO MEDIAL TRACTION, LATERAL COMPRESSION, AND POSTERIOMEDIAL SHEAR FORCES. FACTORS ATTRIBUTED TO INJURY SEVERITY INCLUDE OVERUSE, POOR THROWING MECHANICS, ORTHOPEDIC MATURITY, AND REDUCED MUSCLE STRENGTH. THE ANTERIOR BAND OF THE ULNAR COLLATERAL LIGAMENT (UCL) IS THE MAIN STRUCTURE TO WITHSTAND TENSILE STRESS IN PITCHERS. WHEN OVERWHELMED, LIGAMENT RECONSTRUCTION IS REQUIRED THROUGH A PROCEDURE KNOWN AS TOMMY JOHN SURGERY. PART I OF THE 2 PART SERIES PRESENTS A BASEBALL BAT TRAINING STRATEGY TO IMPROVE MUSCULAR SUPPORT FOR THE PITCHING ELBOW IN PROTECTING THE UCL.

Department of Exercise and Nutrition Sciences, School of Public Health and Health Professions, University at Buffalo, Buffalo, New York

Ryan L. Crotinis a doctoral candidate in the Department of Exercise Science at the University at Buffalo

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Dan K. Ramseyis an assistant professor in the Department of Exercise Science at the University at Buffalo.

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INTRODUCTION

Approximately 2 million youths are exposed to medial elbow injury risks through participation in amateur baseball, otherwise known as little leaguer's elbow syndrome (17). Factors predisposing someone to little leaguer's elbow are known to be poor throwing mechanics, bone plasticity, ligamentous laxity, physeal plate ossification maturity, body composition, and reduced muscle strength (4,13,14,17).

Despite improved coaching and advances in sport biomechanics, medial elbow injuries continue to escalate among competitive baseball pitchers (5,10). Valgus stress (tensile force acting on the soft tissues of the medial elbow) is the primary mechanism associated with medial elbow injury (1,2,4,9,13,14,23). Susceptibility varies according to how the soft tissues counter valgus stressors and ossification maturity of the medial epicondyle apophysis among youth participants (18). Recovery on average requires 3 months rehabilitation and exclusion from sport participation, whereas adults with ulnar collateral ligament (UCL) rupture warrants up to a year (17).

Adults respond differently to valgus stressors because ligamentous failure likely occurs rather than growth plate inflammation and distraction (17). In cadaveric studies examining the valgus stress responses of the UCL and medial elbow musculature, the UCL is reportedly the prominent static stabilizer, which is able to withstand 50% of applied valgus loads with the elbow in 90° flexion (4,14,24). Specifically, the anterior band of the ulnar collateral ligament (aUCL) provides the greatest tensile resistance during overhead throwing activities (4,14,24). Its failure has been implicated with repetitive throwing, for which Tommy John surgery has been a common procedure for reconstructing the ligament.

During pitching, valgus torque exceeds the failure point of the aUCL almost 2-fold (4,10,14,24), suggested to be influenced by muscular synergists that control functional elbow range of joint motion. Termed “dynamic stabilization,” the muscles spanning the medial elbow (flexor-pronator muscle mass) are thought to provide significant dynamic restraint. Muscle contraction acts to counter valgus forces by inducing a varus moment, which in theory protects the UCL from tensile overload by compressing the medial elbow while concurrently protecting the lateral elbow from high compression forces (4,10,14,24). However, dynamic stability may be compromised because of poor throwing mechanics, joint inflexibility, conditioning, and muscle fatigue from overuse, which places pitchers at greater risk for injury (4,10,14,16,19,20,24).

This article is the first of a 2-part series that presents injury prevention information concerning: (a) varus elbow torque and dynamic stabilization, (b) evaluation of the throwing elbow, and (c) baseball bat training to promote medial elbow strength. The second in the series will highlight proximal and contraindicated exercises for the throwing arm to further reduce medial elbow injury risks. In this article, the “pitchers' baseball bat program” is a preventive training initiative that uses a baseball bat and simple techniques to improve strength and endurance of the medial elbow static and dynamic stabilizers, with the goal of reducing elbow injury rates. As described, the dynamic stabilizers support static stabilizers, which include (a) the accessory ligaments, (b) capsular tissue, and (c) articular components about the anatomical joints. Injury prevention programs specific to the throwing athlete are most successful when integrating both muscular force capacity and endurance exercise concurrently, as both stimuli reduce the risk of repetitive strain injuries (15). Expected outcomes include improved throwing arm health and pitching performance and participant longevity with associated reductions of repetitive strain injuries throughout one's baseball association.

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INJURY ETIOLOGY: VARUS ELBOW TORQUE AND DYNAMIC STABILIZATION

The primary etiology responsible for medial elbow injuries is attributable to significant and repetitive valgus force to the medial elbow during the late cocking and acceleration phases of throwing. During overhand throwing, interactive joint moments transition through the kinetic chain, beginning with the lower body and proceeds through trunk rotation where significant internal shoulder moments accelerate the upper extremity forward, during which the greatest amount of valgus stress to the elbow is generated (11). The transition between cocking and acceleration begins with the shoulder maximally externally rotated (MER) and abducted 90–110°. In this position, the internal rotators and horizontal adductors (pectorals, subscapularis, and latissimus dorsi) of the shoulder are loaded eccentrically, which during the acceleration phase transfer elastic energy to accelerate the throwing arm forward as the shoulder internally rotates and horizontally adducts about the proximal humerus (5,11,22). The humerus counterrotates about its long axis (torsion), with the proximal end internally rotating and the distal end externally because the forearm lags behind the upper arm as a result of its inertia (10,14,22,24). During this phase, valgus strain may exceed the tensile strength of the UCL, predisposing it to chronic microdamage or acute rupture. Estimates of valgus moments measured dynamically using 3-dimensional motion analysis have been shown to be significantly higher than cadaveric measures of ultimate tensile strength for the a-UCL.

One important determinant of pitch-related fatigue to consider may be changes in elbow muscle function, as evidenced by force reductions in the dynamic stabilizers that elicit elbow varus moments (10,14,22,24). Alterations in neuromuscular activity, both in timing and sequencing, valgus torque loading rates, and magnitudes of varus-directed forces are known to be correlated with greater elbow valgus stress (10,14,22,24). Insufficient elbow varus moments (rotational forces that counteract the opening of the medial elbow) may precipitate medial elbow injury (2–4,14,22,23).

In response to the valgus moment that elicits medial opening, an internal varus moment is applied medially across the elbow joint with each pitch in response to opening of the medial elbow compartment (1,3). The varus moment reduces tensile stress, controls compression about the lateral elbow, and aids in accelerating the throwing forearm, hand, and baseball until ball release (4,10,14,22,24). Valgus moments during pitching have been established at 120 N·m, where the failure of the UCL has been reported at 34 N·m (24). This discrepancy between biomechanical and cadaveric torque values indicates the importance of dynamic stability.

Muscles spanning the elbow act as the primary dynamic stabilizers, where they function as agonists, synergists, and cocontractors in response to valgus stress (12,14,21). Specifically, the biceps brachii, brachialis, brachioradialis, triceps brachii, and common flexor-pronator group (flexor-pronator mass [FPM]) offer the greatest degree of resistance to medial opening (12,14,21). An electromyographic analysis of the FPM during the pitching sequence revealed UCL insufficiency concomitant with decreased neural drive (12,14,21). Given this observation, a concentrated strength and conditioning regimen to offset laxity and neural deficits is warranted to protect the integrity of the UCL (12,14,21).

The FPM originates from the medial epicondyle of the humerus and includes the pronator teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and the flexor digitorum superficialis (21). The antagonist action between the UCL and FPM counters the valgus torques by applying a net varus force (2,4,14). Minimal dynamic stabilization is offered by the FPM when high joint congruency angles are achieved. At 0–5° elbow flexion (terminal extension), olecranon fossa contact between the olecranon process and distal humerus stabilizes the elbow and at elbow flexion greater than 135°, and contact between the radial head and capitellum resists joint mobility (14). During the pitching delivery, dynamic stability is critical because the throwing arm does not achieve close packed positions where the elbow maintains angles between 125 and 20° flexion from early cocking to ball release (1,7,8). The 2 most important dynamic stabilizers that protect the UCL throughout the dynamic range of throwing are the flexor carpi ulnaris and flexor digitorum superficialis. Between 5 and 135° of elbow flexion, both assist the UCL in stabilizing valgus stress at the medial elbow, with the flexor carpi ulnaris the significant contributor (4,14). The anatomical orientation of flexor carpi ulnaris and flexor digitorum superficialis overlays the UCL and establishes a parallel summative force vector with the UCL to produce strong varus torques (15,21,24).

Forearm rotation may be a secondary protective element to combat valgus stress. Fastballs and changeups are thrown with the forearm pronated for most of the pitching sequences, from MER to ball release (6). In contrast, when throwing the curveball, the forearm is supinated at MER, where valgus torques are highest and the absence of pronation (pronator teres activation) may account for the higher incidence for injury (6).

Cadaveric studies examining passive resistance to valgus stress with the forearm either supinated, in neutral, or pronated do not adequately reflect baseball pitching because forearm pronation reduces passive tension, furthering UCL instability to valgus stress (24). Passive tension provides valgus/varus support as musculotendinous units are stretched, where deficient UCLs can be passively stabilized under forearm supination (24). Although passive stabilization offers some benefit to high velocity joint actions, active tension hallmarked by synchronous neural firing, muscular strength and endurance of the flexor carpi ulnaris, flexor digitorum superficialis, and pronator teres show greater compression capacity of the medial elbow (4,15,21,24).

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EVALUATION OF THE THROWING ELBOW: RANGE OF MOTION ASSESSMENTS

Comparisons between the throwing elbow and nonthrowing elbow are imperative for identifying structural abnormalities, instability, and range of motion deficits (4,14). Often, reduced range of motion is indicative of joint contracture or fragmentation (2,4,14). However, the stresses accumulated during repetitive throwing may elicit other musculoskeletal conditions that do not present pain or dysfunction (2,4,14). To identify and monitor the acute or chronic nature of injury during sport participation, frequent elbow screenings throughout the competitive season are advocated. Examinations by physical and athletic therapists should include inspection and palpation of all pertinent elbow structures and function, goniometric evaluations of elbow range of motion, and varus and valgus stress measures of the elbow based on manual muscle tests to assess stability (18).

Normative passive range of motion is reportedly 0–140° (sagittal plane forearm rotation), 80–90° for pronation and supination (axial forearm rotation), and 11–15° for valgus alignment (frontal plane forearm rotation) (4,17). The carrying angle specifies the degree of valgus alignment (frontal plane forearm rotation), where increased laxity predisposes athletes to valgus-related pathologies. The carrying angle is formed by the humeral and ulnar axes when the elbow is at maximum extension and the forearm maximally supinated. Normal carrying angles for adults are between 11 and 15° valgus, whereas among adult pitchers, magnitudes beyond 15° valgus alignment are common (4,17). Greater frontal plane range of motion is indicative of ligamentous laxity that is exacerbated by chronic stretch leading to elbow instability, for which treatments are rest, rehabilitation, or surgery. Coordinated high angular joint velocities required in throwing the baseball greatly affect performance. But the presence of instability or other musculoskeletal maladaptation that restricts range of motion is detrimental to joint integrity and elbow health. Therefore, a clear understanding of the etiology and sport-specific biomechanics responsible for elbow injury will lead to improvements in rehabilitative strategies and surgical treatment (2,4,14).

Clinical symptoms associated with loss of joint motion should be examined because pain or effusion is suggestive of capsular sprain, flexor strain, loose body formations, or chondral irregularities (4,17). Elbow hyperextension is uncommon among adult pitchers considering that nearly half exhibit pain-free elbow flexion contractures, although whether performance and health are impacted remain unknown (2,4,17). Elbow contractures are managed by regular static stretching of the biceps brachii, brachialis, brachioradialis, and flexor muscles. In some instances, adaptive contractures may be a protective mechanism in decelerating the throwing arm (4,8).

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EVALUATION OF THE THROWING ELBOW: FUNCTIONAL VALGUS STRESS TESTS

A common manual test to assess valgus instability is the passive valgus stress test. With the arm fully relaxed and slightly abducted and the elbow positioned 20–30° in flexion, a valgus stress is applied to the medial elbow (Figure 1). Because outcomes differ depending on axial forearm rotation, the valgus stress test is performed with the forearm supinated and pronated (2,4,15,22). With the forearm maximally pronated, less than 1 mm of medial compartment opening is considered normal (4). Valgus extension overload (VEO) is examined using the valgus extension test to confirm posteromedial olecranon impingement, posteromedial osteophytes, and the presence of loose bodies (2,4,22). The elbow is flexed roughly 30°, which unlocks the olecranon tip from the olecranon fossa, and a valgus force is applied while the elbow is simultaneously extended. The Milker's maneuver depicted in Figure 2 (also considered valgus extension test or moving valgus stress test) requires the examiner to pull the person's thumb while the forearm is supinated, the shoulder abducted 90°, and elbow in 90° flexion (22). From this initial position, the elbow is moved through full flexion and extension to identify points of apprehension, instability, or UCL pain. VEO, a posteromedial elbow injury mechanism that combines valgus stress and forceful triceps extension, is the primary cause of olecranon osteophyte formation among throwing athletes and can be replicated using either of these functional tools (4,22).

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BASEBALL BAT TRAINING PROMOTES MEDIAL ELBOW STRENGTH

From an injury prevention perspective, the pitchers' baseball bat program is designed to strengthen the capsuloligamentous and musculotendinous elbow components by enhancing tensile strength, neural drive, and recovery capacity of the FPM to improve varus torque capacity. The intention is to reduce both risk and severity of medial epicondyle apophysitis, FPM tendinopathies, and avulsion fractures of the medial epicondyle. However, improper pitching mechanics through iterative movement patterns predisposes the elbow to increased valgus stress that may exceed the tensile strength of the UCL, causing either chronic microscopic tears or acute rupture. Therefore, the mechanical deficiencies should also be corrected when presented, with emphasis on how pitchers establish MER during the late cocking phase and transitioning from MER to maximum acceleration of the forearm and hand to ball release. Implementing this preventative exercise regimen into the conditioning repertoire combined with effective pitching delivery will ensure healthy sport participation and lessen the incidence of repetitive stress injury.

The prescribed exercises listed in the Table depict sequence order, bat lengths for varying resistance, and training volume. Routines are performed separately using both arms and are to be completed post pitching and during the athlete's off days. Resistance is adjusted by altering where one grips the baseball bat. During the first 3 weeks of the program, athletes begin by gripping half the bat length. Once familiarity and preconditioning are achieved, athletes at or approaching skeletal maturity (ages 15 and above) may increase resistance by gripping three quarters grip of the baseball bat. Gripping half the bat reduces the moment inertia and lowers resistance to forearm rotation. Anyone younger than 15 years should not advance beyond half the length of the baseball bat. Emphasis here is on training muscular endurance. High repetition has been shown to prevent musculoskeletal injuries by strengthening muscles, tendons, ligaments, and accompanying soft tissues (Table) (14).

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  • Overhead pronation-supination: Holding the baseball bat with the elbow flexed about 30°, and the hand is positioned at a height approximating where the ball is released. In this position, both the triceps and biceps coactivate, which mediates elbow compression, and simultaneous forearm rotation is enacted by the pronator teres and supinator muscle groups (Figure 3).
  • Neutral wrist radial bat circles: Begin by grasping the baseball bat with the head directed vertically (radial direction), flex the elbow 90° and hold the wrist in a neutral position, and rotate the head of the bat using small circular oscillations in both clockwise and counterclockwise directions (Figure 4).
  • Neutral wrist ulnar bat circles: The baseball bat is held with the head directed downward (ulnar direction), the elbow flexed 90°, and the wrist in neutral position. Similar to radial bat circles, rotate the head of the bat using small circular oscillations in both clockwise and counterclockwise directions (Figure 5).
  • Radial bat deviations: Hold the baseball bat with the head of the bat oriented vertically (radial direction), the elbow in 90° flexion, and wrist in neutral orientation. Move the bat head forward and backward similar to a hammering maneuver. When using the half grip, cover the elbow using the nonactive hand to shield it from coming in contact with the knob of the bat (Figure 6).
  • Ulnar bat deviations: With the elbow flexed 90° and the wrist in neutral position, hold the bat so that the bat head is downward (ulnar direction). Move the bat head anteriorly and posteriorly in a manner similar to radial bat deviations. Cover the elbow using the nonactive hand as described earlier (Figure 7).
  • Resisted bat pronation at full supination: Begin with the elbow flexed about 30° and grip the bat with a supinated wrist. Your partner will provide dynamic resistance, moving from maximal supination until neutral wrist alignment, or a “thumbs-up” position is achieved. It is important that both partners communicate to provide appropriate resistance. Too much resistance prevents sufficient repetitions, whereas minimal resistance inadequately strengthens the muscles. Repetitions between 10 and 15 allow for adjustments in resistance (Figure 8).
  • Neutral wrist eccentric pronation: Holding the baseball bat with bat head vertical, your partner forces the bat to rotate causing the wrist to supinate. Resistance is attempted by trying to maintain wrist pronation. Exercise ceases when the wrist achieves full supination. Again, partner communication is essential to avoid injury. Young athletes should be closely monitored to provide appropriate resistance for 10–15 repetitions to maximize conditioning and avoid the risk of injury (Figure 9).
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SUMMARY

It is widely acknowledged that the majority of youth baseball injuries are preventable (25), which supports the implementation of the pitchers' baseball bat program initiative.

Insufficient, inappropriate, or the lack of injury prevention practices may impact long-term health care costs given onset and severity of pediatric injuries involving repetitive strain or acute throwing stress which predispose youth to growth plate deformity, such as bone shortening that consequently increases the likelihood of reinjury in adulthood (18). Capsuloligamentous and musclulotendinous elastic deformation responds to bone growth at muscle-tendon-bone interfaces, for which reduced bone length can affect stabilization tension provided by UCL and dynamic stabilizers (18).

To promote healthy participation in baseball and lessen the incidence of repetitive stress injury, annual elbow examinations are advocated. This may facilitate early detection of maladaptive or orthopedic changes that arise from cumulative loading during repeated baseball pitching. Youth should not be enrolled in overhead sports that demand more than 9 months of involvement. In addition, age-appropriate pitch counts with sufficient days off to promote recovery should be strictly adhered to. Any mechanical deficiencies should be corrected when presented. Finally, the pitchers' baseball bat program is a training initiative that uses a baseball bat and simple techniques to improve both strength and endurance of the medial elbow stabilizers. Routines are to be performed separately using both arms and completed post pitching and during off days. Success is predicated on strict monitoring by coaches, athletic trainers, physical therapists, and parents, all of whom are integral for reinforcing consistency and correct technique. Although beyond the scope of this article, complete throwing arm conditioning should also integrate rotator cuff, scapular stabilization, and back and core abdominal exercises to maximize and enhance movement synergy between the lower and upper body throughout the pitching delivery. By integrating this exercise regimen early into the conditioning repertoire and with continued use, the incidence of youth and adult elbow injuries in baseball may be lessened.

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Keywords:

baseball pitchers; throwing arm injuries; baseball injury prevention; baseball training; Tommy John surgery

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