Abstract
There are many sports that involve overhead throwing, such as baseball, softball, cricket, football, soccer, water polo, javelin throw, as well as many others. Throwing is a complex motion involving transfer of energy through the entire kinetic chain from the lower extremities to the upper extremities and finally to an object to propel the object away from the thrower. This results in large stresses being placed on the thrower’s musculoskeletal system, which can potentially result in injury. Repeated application of these stresses to the thrower’s body also results in overuse injuries. This chapter discusses the stages of the classic throw and the injuries generally incurred during these stages. Most common injuries are in the shoulder and the elbow; other joints can be involved but are significantly less so, such as the wrist, back, hips, or knees.
Keywords
overhead throw, baseball, rotator cuff, internal impingement, elbow, ulnar collateral ligament (UCL)
Key Concepts
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The overhead throw involves complex motions through the shoulder, elbow, and wrist.
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Proper mechanics involve distribution of energy through the kinetic chain from the lower extremity push-off, to pelvic and torso rotation, and into elbow extension and shoulder rotation.
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Lower extremity propulsion and body rotation produce 50% of the velocity of a throw.
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Inadequate leg and core strength necessitates increased upper extremity forces to achieve high velocities. This places the thrower at increased risk of injury.
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Extreme forces placed on the shoulder and elbow during repetitive throws often cause microtrauma to the surrounding soft tissues, leading to overuse injuries.
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There are many different techniques of throwing mechanics, yet the “classic throw” (baseball throw) is the most common.
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Injuries can occur in traditional throwing sports (e.g., baseball) as well as repetitive overhead motion sports (e.g., swimming and tennis).
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Different sports and types of projectiles require different types of throws (e.g., a football pass differs from a baseball pitch).
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Decreased range of motion, lower joint forces, and lower velocity of football pass when compared to baseball pitch.
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Different sports can yield different injuries (e.g., football injuries are typically from trauma whereas baseball injuries are typically due to overuse).
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Isolating what phase of the throw the pain or dysfunction is in can be helpful in diagnosis.
Phases of the Classic Throw
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The throw is generally divided into six phases:
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Wind-up
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Early arm cocking (stride)
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Late arm cocking
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Arm acceleration
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Arm deceleration
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Follow-through
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Wind-up phase
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Purpose is to begin to build potential energy.
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Uses very little energy
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Requires motion through the hip and torso to generate full potential energy
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The wind-up phase begins with the throw initiation and ends as the stride leg moves toward the target ( Fig. 29.1A and B ).
Fig 29.1
The sequence of motion of the early phases of throwing from throw initiation (A) , to the windup (B) , and then into the early cocking phase (C) .
(Modified from Park S, Loebenberg ML, Rokito AS, Zuckerman J, The shoulder in baseball pitching: biomechanics and related injuries—part 1. Bull Hosp Joint Dis. 2002–2003;61:68–79.)
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Few injuries occur during this phase.
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Early arm cocking phase (stride)
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Purpose is to initiate the vector of force at the target and begin transition of potential energy to kinetic energy.
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The early arm cocking phase (or stride phase) begins with hand separation and ends when the foot contacts the ground (see Fig. 29.1C ).
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The hind foot pushes off, and the pelvis and torso rotate to move the thrower toward the target.
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Shoulder movements include glenohumeral abduction, external rotation, and scapular upward rotation.
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Almost no injuries occur during this phase, but lack of flexibility and proper positioning can lead to overloading of the shoulder in later phases.
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Late arm cocking phase
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Purpose is to produce maximal external rotation of the shoulder to allow for full transfer of force to the object being thrown.
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Begins as the stride foot contacts the ground and ends as shoulder internal rotation begins ( Fig. 29.2A )
Fig 29.2
The sequence of motion of the late phases of throwing from the late cocking phase (A) , to the acceleration phase (B) , and ending with the deceleration phase and follow-through (C) .
(Modified from Park S, Loebenberg ML, Rokito AS, Zuckerman J. The shoulder in baseball pitching: biomechanics and related injuries—part 1. Bull Hosp Joint Dis. 2002–2003;61:68–79.)
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Maximal external rotation occurs at the shoulder.
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This can lead to impingement between the superior rotator cuff and the labrum.
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The inferior glenohumeral ligament and the long head of the biceps muscle prevent anterior translation of the humeral head.
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The rotator cuff muscles contract to center the humeral head on the glenoid.
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Strong valgus forces applied to medial elbow
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Wrist and hand in hyperextension position
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Acceleration phase
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Purpose is to transfer all the energy from the trunk to the object being thrown in a vector toward the target.
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Begins with shoulder internal rotation and ends with ball release (see Fig. 29.2B )
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Most forceful phase
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Transition of trunk from hyperextension to forward flexion
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Wrist goes from hyperextension to neutral
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Large rotational torque placed on the soft tissues of the shoulder
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Elbow extension begins, causing increased elbow forces. Maximal valgus stress is in this phase.
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Humerus should be aligned in the plane of the scapula.
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Ulnar collateral ligament is under maximal valgus stress, preventing elbow instability.
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Deceleration phase
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Purpose is to dissipate excess energy from acceleration phase that was not transferred to the thrown object.
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Begins at ball release and ends when shoulder reaches maximal internal rotation and terminal elbow extension (see Fig. 29.2C ).
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Rotator cuff muscles contract to oppose internal rotation and glenohumeral distraction.
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Large traction force applied to the long head of the biceps to decelerate extending elbow.
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A longer deceleration phase reduces risk of injury, as this spreads the dissipation of energy out over a longer path.
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Follow-through phase
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Purpose is to finish dissipation of energy from deceleration phase and return to a “ready” position for another action.
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Begins at maximal shoulder internal rotation and ends when thrower returns to a balanced stance (see Fig. 29.2C )
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Arm adducted across the body
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Movements of trunk flexion and lead knee extension help dissipate deceleration force into large muscle groups.
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No primary injuries occur during this phase; however, the thrower may experience elbow pain if posterior impingement is limiting full elbow extension.
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Pathology
Shoulder Injuries
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Extreme external rotation can cause anterior laxity of the glenohumeral joint capsule, leading to instability and impingement ( Fig. 29.3 ).
Fig 29.3
Internal impingement of the undersurface of the rotator cuff against the posterior aspect of the labrum in maximum external rotation and abduction.
(From Braun S, Kokmeyer D, Millett P. Shoulder injuries in the throwing athlete. J Bone Joint Surg Am . 2009;91:966–978.)
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Internal impingement syndrome: anterior instability during external rotation causes the rotator cuff tendons and the labrum to be pinched between the greater tuberosity of the humeral head and the posterior superior glenoid.
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Internal impingement may lead to a variety of problems: rotator cuff tendon fraying, chondromalacia of the humeral head, superior labrum anteroposterior lesions/tears (SLAP).
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Subacromial impingement may occur as the humerus is internally rotated (see Chapter 33 ).
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Younger pitchers typically have internal impingement, whereas older pitchers tend to have subacromial impingement.
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Anterior laxity can increase strain on the biceps tendon, causing bicipital tendonitis (see Chapter 31 ).
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Laxity can develop in the posterior shoulder capsule as microtears occur during resisted glenohumeral distraction.
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Posterior laxity produces instability and painful glenohumeral subluxation (see Chapter 28 ).
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Rotator cuff injuries
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Eccentric rotator cuff forces may eventually lead to tears (see Chapter 34 ).
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Repeated impingement may lead to tears (as discussed previously).
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Articular sided tears at the junction of the infraspinatus and supraspinatus are commonly found.
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Labral tears
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SLAP lesions (see Chapter 30 ).
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During deceleration phase, traction occurs at insertion of long head of biceps.
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Often occur concomitantly with rotator cuff tears
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Glenohumeral internal rotation deficit (GIRD)
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Glenohumeral internal rotation deficits caused by posterior capsular tightness can also contribute to internal impingement.
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Glenohumeral internal rotation deficits should be suspected if internal rotation range of motion is decreased in the throwing arm compared with the nonthrowing arm ( Fig. 29.4 ).
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