Overhead throwing activities expose the elbow to tremendous valgus stress, making athletes vulnerable to a specific constellation of injuries. Although baseball players, in particular pitchers, are the athletes affected most commonly, overhead throwing athletes in football, volleyball, tennis, and javelin tossing also are affected. The purpose of this review is to review the anatomy, biomechanics, pathophysiology, and treatment of elbow disorders related to overhead throwing athletes. Although focus is on management of ulnar collateral ligament injuries, all common pathologies are discussed.
Key points
- •
Most elbow injuries occur as a result of the stresses incurred during the acceleration phase.
- •
During overhead throwing, a large valgus force on the elbow created by humeral torque is countered by rapid elbow extension, creating significant tensile stress along the medial compartment, shear stress in the posterior compartment, and compressive stress in the lateral compartment.
- •
The docking technique in ulnar collateral ligament (UCL) reconstruction demonstrated a lower complication rate and a greater rate of return to play compared with the Jobe technique.
- •
During surgical management of valgus extension overload syndrome, it is recommended that only the osteophyte and no native olecranon be removed to prevent iatrogenic instability.
Introduction
The elbow undergoes significant stress during the throwing motion of an overhead athlete. The forces generated in the various phases of the throwing arc are distributed through the soft tissue and bone of the elbow joint. In athletes, such as baseball players, repetition leads to attritional damage to the elbow. The specific constellation of injuries suffered in baseball and other overhead sports, such as softball, football, tennis, and javelin, are well documented. These injuries include (1) medial UCL tears, (2) ulnar neuritis, (3) flexor-pronator injury, (4) medial epicondyle apophysitis or avulsion, (5) valgus extension overload syndrome with olecranon osteophytes, (6) olecranon stress fractures, (7) osteochondritis dissecans (OCD) of the capitellum, and (8) loose bodies.
Approximately 55% of high school students participate in sports, and in 2013, softball and baseball ranked as the forth and third most popular high school sports for girls and boys, respectively. More than 2 million high school athletes are seen for sports-related injuries on an annual basis. Although the rate of elbow injuries is relatively low, the total number of such injuries is significant due to the high number of participants. With increasing rates of adolescent and young adults participating in athletics, knowledge regarding the diagnosis and treatment of thrower’s elbow remains prudent. The elbow joint is complex, however, and understanding the management of thrower’s elbow injuries begins with understanding the anatomy and pathophysiology.
The purpose of this review article is to describe the biomechanics of the throwing motion, the examination of the elbow, the diagnostic evaluation, and the diagnosis and treatment of the spectrum of elbow injuries common to a thrower ( Box 1 ).
UCL injury
Ulnar neuropathy
Flexor-pronator injury
Medial apophysitis or epicondyle avulsion
Valgus extension overload syndrome
Olecranon stress fracture
OCD of the capitellum
Introduction
The elbow undergoes significant stress during the throwing motion of an overhead athlete. The forces generated in the various phases of the throwing arc are distributed through the soft tissue and bone of the elbow joint. In athletes, such as baseball players, repetition leads to attritional damage to the elbow. The specific constellation of injuries suffered in baseball and other overhead sports, such as softball, football, tennis, and javelin, are well documented. These injuries include (1) medial UCL tears, (2) ulnar neuritis, (3) flexor-pronator injury, (4) medial epicondyle apophysitis or avulsion, (5) valgus extension overload syndrome with olecranon osteophytes, (6) olecranon stress fractures, (7) osteochondritis dissecans (OCD) of the capitellum, and (8) loose bodies.
Approximately 55% of high school students participate in sports, and in 2013, softball and baseball ranked as the forth and third most popular high school sports for girls and boys, respectively. More than 2 million high school athletes are seen for sports-related injuries on an annual basis. Although the rate of elbow injuries is relatively low, the total number of such injuries is significant due to the high number of participants. With increasing rates of adolescent and young adults participating in athletics, knowledge regarding the diagnosis and treatment of thrower’s elbow remains prudent. The elbow joint is complex, however, and understanding the management of thrower’s elbow injuries begins with understanding the anatomy and pathophysiology.
The purpose of this review article is to describe the biomechanics of the throwing motion, the examination of the elbow, the diagnostic evaluation, and the diagnosis and treatment of the spectrum of elbow injuries common to a thrower ( Box 1 ).
UCL injury
Ulnar neuropathy
Flexor-pronator injury
Medial apophysitis or epicondyle avulsion
Valgus extension overload syndrome
Olecranon stress fracture
OCD of the capitellum
Functional anatomy
The elbow is a ginglymus joint that allows flexion-extension through the ulnohumeral articulation and pronation-supination through the radiocapitellar articulation. It is one of the most congruent joints in the body, with the trochlea covered by articular cartilage over a 300° arc. The bony anatomy of the proximal ulna and olecranon fossa provides primary stability at opposite ends of terminal motion: less than 20° and greater than 120° of flexion. The radial head provides secondary restraint to valgus stress at 30°. The primary stability during the functional arc of an overhead athlete (20°–120°) emanates from the soft tissue restraints. Furthermore, much of the stability derived from the osseous structure resists against varus stress with the elbow in extension.
The soft tissue structures that provide static valgus elbow stability vital to overhead throwing include the anterior joint capsule, the UCL complex, and the radial collateral ligament complex. The UCL is composed of 3 bundles: an anterior, a transverse oblique and a posterior. The anterior bundle provides valgus stability throughout the entire range of motion (ROM) and consists of anterior and posterior bands that originate from the inferior aspect of the medial epicondyle and insert at the sublime tubercle on the medial aspect of the coronoid process ( Fig. 1 A–D). The anterior band provides primary stability against valgus stress from full extension to 90° of flexion and secondary restraint at flexion greater than 90°. The posterior band, which is nearly isometric, provides functionally important restraint between 60° and full flexion, an arc of motion pivotal in the motion of an overhead throwing athlete.
The oblique bundle (transverse ligament) lies at the distal-medial aspect of the joint capsule and does not actually cross the elbow joint. The posterior bundle is thinner and weaker than the anterior bundle and provides secondary elbow stability at greater than 90° of flexion.
The dynamic elbow stabilizers consist of the muscles in the flexor-pronator mass that originate off the medial epicondyle. This mass consists of the pronator teres, flexor carpi radialis, palmaris longus, flexor digitorium superficialis, and flexor carpi ulnaris (FCU), which functionally stabilize against valgus stress during active motion.
Lastly, the ulnar nerve courses the medial elbow joint emanating from the arcade of Struthers and passing into the posterior compartment of the arm through the medial intermuscular septum. The nerve, along with a rich plexiform of vessels, enters the cubital tunnel just posterior to the medial epicondyle. The UCL complex forms the floor of the cubital tunnel whereas the roof is composed of the arcuate (Osborne) ligament. Distally, the ulnar nerve passes between the 2 heads of the FCU and rests on the flexor digitorum profundus.
Biomechanics of throwing
Overhead throwing sports are typically grouped together because the general motion is similar. Thus, a baseball pitcher’s throwing motion, which is the most heavily investigated model, serves as the basis for understanding biomechanics. The baseball pitch is divided into 6 stages of coordinated upper extremity, trunk, and lower extremity movements ( Fig. 2 ). The stages specific to elbow motion include
- I.
Wind-up: the elbow is flexed and the forearm is pronated as the arm is initially overhead and returns to an adducted position.
- II.
Early cocking: the elbow maintains flexion and forearm pronation as the glenohumeral joint is abducted and externally rotated and the leading lower extremity is advanced.
- III.
Late cocking: involves increasing elbow flexion between 90° and 120° and forearm pronation to 90° while maximizing shoulder abduction and external rotation.
- IV.
Acceleration: the elbow is rapidly extended as the humerus adducts and internally rotates during a coordinated forward movement of the upper extremity and trunk. This stage terminates with ball release over 40 to 50 milliseconds, during which the elbow accelerates as much as 600,000°/s.
- V.
Deceleration: rapid deceleration occurs at a rate of 500,000°/s 2 over a time span of 50 milliseconds as excess kinetic energy is dissipated.
- VI.
Follow-through: the elbow reaches full extension and throwing motion terminates.
Most elbow injuries occur as a result of the stresses incurred during stage IV or the acceleration phase where valgus forces reach as high as 64 Nm. The valgus torque concentrate to the medial elbow, primarily the anterior bundle of the UCL. Approximately 300 N of shear force is experienced by the medial elbow. Concomitantly, compressive forces at the lateral radiocapitellar joint reach 500 N. Nevertheless, modification to throwing biomechanics may not necessarily lead to improved clinical outcomes because the stresses from repetitive throwing may be the driving force to injury.
Developmental changes of the elbow
The repetitive stresses at the elbow and shoulder from throwing can lead to developmental changes, and, eventually, injury in young athletes. Small adaptive changes proximally may affect more distal segments of the kinetic chain. For instance, Garrison and colleagues found deficits in total ROM of the shoulder were associated with UCL tears in a cross-sectional study of high school and collegiate baseball players. Changes in the shoulder include increase in external rotation from humeral retroversion and capsular laxity as well as decrease in internal rotation from osseous adaptations. Polster and colleagues demonstrated that the mean dominant arm humeral torsion in professional pitchers was 38.5° ± 8.9° (range, 23.0°–53.9°) compared with 27.6° ± 8.0° (range, 11.8°–45.0°) in the nondominant arm. This adaptation may be protective because the investigators found a higher incidence of severe injuries in players with lower degrees of dominant torsion. Burkhart and colleagues proposed that increased humeral torsion leads to greater external rotation of the shoulder during late cocking, thus providing a longer throwing arc and potentially a greater peak velocity that increases the stresses experienced by the elbow. Distally at the elbow, Hang and colleagues found that 94% of competitive young baseball players had radiographic signs of medial epicondylar apophyseal hypertrophy.
In overhead throwing athletes, understanding the difference between commonly seen asymptomatic adaptive changes and clinically significant pathology is critical in providing proper care to these athletes. In a study of asymptomatic professional baseball players, Kooima and colleagues found an 87% prevalence of chronic UCL injury and an 81% prevalence of posteromedial osteochondral injury. In asymptomatic major league baseball pitchers, increased medial laxity on valgus stress is not uncommon. In a skeletally immature or adolescent thrower, the physis or apophysis absorbs the stresses of throwing and undergoes changes. With time, asymptomatic changes may progress to symptomatic pathology with increased stress or frequency beyond reparative potential.
Pathophysiology of elbow injuries
King and colleagues described a spectrum of elbow injuries in baseball pitchers from medial tension overload to extension overload to lateral compression overload. These injury patterns can be explained by one mechanism: valgus extension overload syndrome. During overhead throwing, a large valgus force on the elbow created by humeral torque is countered by rapid elbow extension creating significant tensile stress along the medial compartment, shear stress in the posterior compartment, and compressive stress in the lateral compartment. Repetitive, near-failure tensile stresses create microtrauma and attenuation anterior bundle of the UCL, leading to progressive valgus instability. Continued shear stress and impingement in the posterior compartment lead to olecranon tip osteophytes, loose bodies, and articular damage to the posteromedial trochlea in the continuum of valgus extension overload syndrome ( Fig. 3 A, B). As the UCL becomes incompetent, the osseous constraints of the posteromedial elbow become important stabilizers during throwing. Subtle laxity in the UCL also leads to stretch of the other medial structures, including the flexor-pronator mass and ulnar nerve. Extrinsic valgus stresses and intrinsic muscular contractions of the flexor-pronator mass lead to tendonitis. Completing the spectrum of thrower’s elbow, ulnar neuropathy is common given the superficial position of the nerve. The nerve is susceptible to injury from traction, compression, and irritation at the medial aspect of the elbow. In any overhead throwing athlete, UCL attenuation or failure must be ruled out but should not be the only pathology considered.
History and physical examination
A thorough history starts with knowing the patients, their sport, and their level of competition. Asking an athlete specifically about the chief complaint may help delineate between primary (ie, decreased velocity on pitch from UCL attenuation) and secondary processes (ie, pain from posteromedial impingement). Complaints may include pain, decreased motion, mechanical symptoms (clicking, locking, popping, and so forth), instability, and paresthesias as well as throwing-specific symptoms. Changes in accuracy, velocity, stamina, and strength aid in diagnosis and serve as markers to measure improvement. Timing of symptoms may not always be clear; however, if a specific injury or event occurred, it is important to know when, how, and whether there were any antecedent or prodromal symptoms. Any changes in a training or throwing regimen should be noted, including pitch counts, innings pitched, games pitched, and rest between pitching for baseball players.
The timing, onset, and frequency of pain are important to determine. In athletes with valgus instability, approximately 85% experience pain during the late cocking and early acceleration phases of throwing.
Physical examination starts with inspection of an athlete’s posture, arm position, muscle mass, and skin. Any asymmetries compared with contralateral extremity should be detected. Elbow flexion to approximately 70° allows the greatest intracapsular volume and may be an indication of effusion. Flexion, at a lesser degree, may be secondary to an extension block from posteromedial olecronan osteophytes. With the elbow in extension and forearm in full supination, the carrying angle can be determined. The normal carrying angle is 11° in men and 13° in women. Lastly, inspect the skin for any ecchymoses or prior incisions.
Palpate the olecranon, medial and lateral epicondyles, radial head, and soft spot to establish the important landmarks of the elbow. Tenderness on palpation of these landmarks may indicate acute fracture, stress fracture, or tendonitis. In skeletally immature athletes, tenderness may indicate injury to the apophysis or physis. Lateral olecranon tenderness to palpation may indicate a stress fracture whereas proximal medial tenderness may be related to impingement. Lastly, palpation of the radial head during an arc of passive supination and pronation can help identify osteochondral defects, joint incongruency, and injury to the annular ligament.
Tenderness over the insertions of the various tendons around the elbow can indicate microtrauma or inflammation. The flexor-pronator mass lies just distal to the medial epicondyle with the arm at 90°. Having patients actively flex the wrist helps identify the tendinous mass, accentuate any pain, and differentiate from UCL pathology. Ranging the elbow from 90° of flexion to approximately 50° to 70° of flexion helps to displace the flexor-pronator mass anterior and exposing the UCL just posterior. Focal swelling and tenderness along the UCL should be concerning. As discussed previously, the UCL has 3 distinct bundles, with the anterior bundle running from the inferior aspect of the medial epicondyle to the medial aspect of the coronoid process.
Directly posterior and distal to the medial epicondyle lies the cubital tunnel, which encloses the ulnar nerve. Palpation of the ulnar nerve from proximal at the arcade of Struthers to distal at the FCU should not elicit any pain. Furthermore, percussion of the nerve should be benign (Tinel sign), but radiating symptoms into the ulnar hand and 2 digits indicate ulnar nerve pathology. The ulnar nerve may be symptomatic, however, even if tenderness is not appreciated. The elbow should be fully extended and then flexed with and without pressure on the nerve proximal to the medial epicondyle. Anterior subluxation of the ulnar nerve can cause local or radiating discomfort.
Stability of the elbow can be assessed with patients in either the supine or seated position. In the supine position, the humerus is stabilized in maximal external rotation and 30° of flexion. With the forearm fully pronated and the elbow flexed 20° to 30° to unlock the olecranon from the olecranon fossa, valgus stress is gradually applied to the elbow and opening is assessed. Less than 1 mm of opening and a firm endpoint should normally be appreciated during the manual valgus stress test. Physiologic laxity may be present, however, and it is more appropriate to compare the stability with the contralateral extremity. Increased opening of the joint space or reproduction of a patient’s pain should raise suspicion of injury to the anterior band of the anterior bundle of the UCL.
The milking maneuver tests the posterior band of the anterior bundle of the UCL. In this maneuver, the forearm is supinated fully and the elbow is flexed beyond 90° (approximately 120°) and the humerus is at the athlete’s side ( Fig. 4 ). The thumb is then pulled laterally by the examiner or the athlete’s contralateral extremity, creating a valgus force on the elbow. Pain, instability, or apprehension is indicative of injury to the UCL.
Lastly, with the patient in the seated position and the forearm supinated, the elbow is slightly flexed. With one hand on the posterior aspect of the distal humerus and the other hand on the volar forearm, the elbow is rapidly extended while applying a valgus stress. Pain with this valgus extension overload test indicates impingement of the posteromedial tip of the olecranon on the medial wall of the olecranon fossa.
Imaging modalities
Standard anteroposterior, lateral, and oblique radiographs are obtained of the elbow. Radiographs may demonstrate calcification of the UCL, osteophytes adjacent to the UCL, olecranon fossa osteophytes, sclerotic OCD lesions, and/or loose bodies. Fluoroscopy is useful in assessing for medial instability by stressing the elbow and comparing with the contralateral extremity. Asymmetry alone, however, may not be enough to diagnose acute injury to the UCL because asymptomatic pitchers have been found to have some laxity in pitching elbow compared with the contralateral extremity. Nevertheless, greater than 3 mm of opening is concerning for UCL injury and valgus instability.
Conventional radiographs are not sensitive for detecting stress injuries in bone. The sensitivity of initial radiographs is as low as 15% and becomes positive over time in only 50% of patients.
Radionuclide bone scanning is sensitive but less specific for detecting osseous stress injuries, even in their early stages. Radionuclide technetium Tc 99m diphosphonate triple-phase scanning can provide the diagnosis as early as 2 to 8 days after the onset of symptoms.
CT can help differentiate between stress fractures and other conditions that may show increased uptake on bone scan ( Fig. 5 ). A CT scan is not sensitive, however, in detecting stress injuries in their early stages.
