Continuing Education Activity

Proximal humeral epiphysiolysis, commonly known as Little League shoulder, is a growth plate overuse injury of the proximal humerus caused by repetitive throwing in skeletally immature athletes. Delayed recognition, inadequate throwing restriction, premature return to sport, and inconsistent workload counseling can lead to prolonged symptoms, recurrence, and rare growth plate complications. This continuing medical education activity addresses the gap between evidence-based evaluation and treatment standards and variable clinical practice in young overhead athletes with shoulder pain. Participants will review typical history and examination findings, appropriate use of radiography and magnetic resonance imaging, nonoperative treatment principles, prevention strategies, and criteria for progressive return to throwing. The activity emphasizes patient-centered counseling, early modification of activity, rehabilitation of modifiable deficits, pitch workload control, and coordination among clinicians, physical therapists, athletic trainers, radiologists, families, and coaches to improve recovery and reduce recurrence.

Objectives:

• Identify clinical and sport-specific risk factors and presenting features consistent with proximal humeral epiphysiolysis (Little League shoulder).
• Interpret appropriate imaging findings to differentiate proximal humeral epiphysiolysis from other causes of shoulder pain in skeletally immature athletes.
• Implement evidence-based management, including throwing cessation, rehabilitation, and graded return-to-throwing with workload modification to reduce recurrence.
• Coordinate interprofessional communication among clinicians, radiology, physical therapists, athletic training, coaches, athletes, and families to align treatment progression and safe return-to-play decisions.

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Introduction

Proximal humeral epiphysiolysis (PHE), commonly known as Little League shoulder, is a shear or stress injury of the epiphyseal cartilage of the proximal humerus that results from repetitive mechanical loading of the skeletally immature shoulder. The condition has also been called osteochondrosis of the proximal humeral epiphysis and rotation stress fracture of the proximal humeral epiphyseal plate.[1] The proximal humerus contains one of the most active physeal regions in the upper extremity, contributing approximately 80% of longitudinal humeral growth. The proximal humeral physis is composed of the humeral head, greater tuberosity, and lesser tuberosity apophyses, which gradually coalesce during adolescence and fuse completely between the ages of 18 and 21. During active growth, the physis is composed largely of cartilaginous tissue, making it weaker than the surrounding ligamentous and musculotendinous structures. Consequently, the physis becomes the path of least resistance when repetitive rotational and shear forces are applied to the shoulder.[2]

By definition, PHE occurs exclusively in athletes whose physis remains open, because closure of the growth plate eliminates the predisposing structural weakness. The condition most commonly presents in youth baseball pitchers aged 11 to 16 years, a period that coincides with peak physeal susceptibility and increased athletic demands.[3] Although PHE is most commonly associated with overhead-throwing athletes, the condition has also been reported in athletes who participate in competitive gymnastics and tennis, indicating that any repetitive upper-extremity loading pattern can produce sufficient stress at the proximal physis to cause injury.[4]

The natural history of PHE is generally favorable when the condition is identified early and managed appropriately. With timely removal from aggravating activity and a structured rehabilitation program, most athletes achieve full resolution of symptoms and return to sport without complications.[1] However, when the diagnosis is delayed, or the athlete returns to activity prematurely, ongoing physeal stress can lead to progressive widening of the growth plate, physeal sclerosis, and, in severe cases, partial or complete physeal arrest, resulting in angular deformity or extremity-length discrepancy.[5]

Etiology

PHE is caused by repetitive loading from overuse of an open proximal humeral physis, most often during overhead throwing. PHE represents a stress injury (microtrauma) to physeal cartilage driven by cumulative mechanical forces rather than an acute, single-event injury.[6] During the throwing motion, the proximal humeral growth plate is exposed to recurrent rotational torque and traction (distractive) forces, particularly with high-pitch volume, high-intensity throwing, and inadequate rest. Over time, cumulative loading can exceed the capacity of the developing physis to remodel, resulting in physeal irritation and stress changes.[2][7]

Risk is amplified by modifiable factors that increase cumulative exposure, including excess pitch counts, year-round play, insufficient off-season recovery, and pitching while fatigued or in pain. Each factor increases total seasonal throws and mechanical stress across the physis, making symptoms more likely and recovery more prolonged if throwing continues.[8] Additionally, the humeral retrotorsion angle has been proposed as another potential factor contributing to PHE. Results from a recent case study suggested that a rapid change in the humeral retrotorsion angle may increase susceptibility to growth plate damage.[9] However, results from other studies indicated that increased humeral retrotorsion does not appear to cause symptoms.[3]

Epidemiology

PHE is seen almost exclusively in skeletally immature overhead athletes, with the highest burden in youth baseball, particularly among pitchers. The condition is typically reported in athletes aged 11 to 16 years, reflecting vulnerability of the open proximal humeral physis during peak throwing volume.[6][7] Across published clinical cohorts, Little League shoulder is predominantly diagnosed in male athletes, largely mirroring participation patterns and pitching workloads in youth baseball. Cases in female athletes and nonbaseball overhead sports have been reported, but they appear far less frequently in the literature.[6]

Precise population-level incidence and prevalence are not well established in the US or globally because most data derive from clinic-based series, case reports, and sport-specific screening studies rather than national surveillance. In one large school-aged baseball cohort of 2044 boys aged 9 to 12 years from Japan, 13.4% reported throwing-shoulder pain. Among those who underwent radiography, a substantial subset demonstrated findings consistent with Little League shoulder, highlighting that the condition is common among symptomatic youth throwers.[10]

Pathophysiology

In the adolescent shoulder, the physis acts as a weak link, with repetitive throwing loads transmitted to the physeal cartilage, rather than to the tendon, capsule, labrum, or rotator cuff, which is more common in adults.[11] The throwing motion has 2 broad phases: the arm-cocking phase and the acceleration phase. The dominant mechanical driver is the repetitive rotational torque that occurs during the late arm-cocking phase of throwing. During this phase, the humerus experiences substantial external rotational stress. Results from biomechanical studies performed in young pitchers supported the concept that this shear stress can deform the relatively weak proximal physeal cartilage. Over time, repeated stress produces microtraumatic injury of the epiphyseal-physeal complex.[3][12]

Although rotational shear is the primary contributor to PHE, repetitive distraction and traction forces across the proximal humerus also contribute. During throwing, the rotator cuff and other dynamic stabilizers act to maintain glenohumeral congruity, and those forces are transmitted to the proximal physis. In the growing athlete, this repeated loading can exceed the capacity of the physeal cartilage to recover, especially during periods of rapid growth, when transient strength-flexibility imbalances can further increase physeal susceptibility to injury.[11][13]

History and Physical

When evaluating a young throwing athlete with suspected proximal humeral epiphysiolysis, the history should focus on progressive throwing-related shoulder pain, prior shoulder symptoms, associated elbow pain, recent changes in throwing mechanics, and whether the athlete has recently undergone a growth spurt. Overuse is most common during adolescence, particularly during periods of rapid growth.[12] Patients may describe an insidious onset of pain that begins during throwing and progresses to pain with arm elevation or even pain at rest. The pain is typically localized to the proximal humerus or lateral shoulder and initially improves with rest. Approximately 10% of patients also describe shoulder fatigue or weakness, and another 13% report concomitant elbow pain.[5] 

Physical examination begins with palpation of the proximal humerus over the physis. The most consistent finding is focal tenderness over this area, particularly over the lateral aspect of the proximal humerus. Swelling, atrophy, weakness, and significant loss of motion are not typically seen. However, shoulder range of motion should be assessed carefully, particularly rotational motion, because a glenohumeral internal rotation deficit has been noted in approximately 30% of patients.[5] 

Evaluation

Evaluation for PHE involves a targeted history, focused physical examination, and plain radiographs. The diagnosis is based mainly on clinical findings, and routine laboratory studies are not typically obtained. Plain radiographs are the first-line imaging study. Shoulder radiographs consisting of anteroposterior views in external and internal rotation are recommended. Widening of the proximal humeral physis on the symptomatic side relative to the contralateral side is considered a hallmark finding of PHE. Comparison radiographs of the contralateral shoulder are helpful because the widening can be subtle. Metaphyseal sclerosis, demineralization or lucency, fragmentation, metaphyseal calcification, cystic changes, or a Salter-Harris type 2 pattern may be seen in more advanced disease. Although these findings are less common, they help support a diagnosis of chronic physeal stress injury.[1][6]

MRI is not typically required when the history, physical examination, and plain radiographs are diagnostic. However, MRI is a preferred second-line study when radiographic findings are normal or equivocal despite clinical suspicion. MRI findings include focal physeal widening, increased signal extending into the metaphysis, marrow edema on the epiphyseal and metaphyseal sides of the physis, periosteal edema, and occasionally mild periosteal elevation. However, MRI abnormalities are also common in asymptomatic Little League players, so results must be interpreted with caution.[14][15][16]

Treatment / Management

The primary treatment for PHE is nonoperative treatment. Immediate cessation of throwing and other painful overhead activities is recommended for at least 3 months. A graduated return to throwing occurs only after the athlete is pain-free and shoulder function has normalized. Notably, the return to throwing should be progressive rather than based solely on time.[5][6] When athletes have a glenohumeral internal rotation deficit, loss of motion, weakness, scapular dysfunction, or abnormal throwing mechanics, clinicians typically add rehabilitation. The focus is restoring the total arc of motion, posterior shoulder flexibility, rotator cuff and scapular stabilization and strength, kinetic chain function, and throwing mechanics.[5]

Differential Diagnosis

The differential diagnosis includes:

• Impingement syndrome
• Rotator cuff injury
• Biceps tendonitis
• Labral tear
• Subdeltoid bursitis
• Fracture
• Proximal humeral osteomyelitis
• Septic arthritis of the shoulder

Less common conditions on the differential diagnosis include:

• Tumors of the upper arm
• C5 radiculopathy
• Thoracic outlet syndrome

Staging

A 3-grade classification of Little League shoulder is based on radiographic findings:

• Grade I: Widening of the epiphyseal plate in the lateral area only
• Grade II: Widening in all areas of the epiphyseal plate and metaphyseal demineralization
• Grade III: Slipped epiphysis [10]

Prognosis

The prognosis for PHE is typically favorable, especially when clinicians make a timely diagnosis and adequate cessation of throwing occurs. Approximately 94% of athletes return to some level of sports participation, and 92.5% return to their preinjury level.[6] However, recurrence after return to sport can occur, with recurrence rates of 7% to 25% documented in the literature. Delayed throwing restriction and worse shoulder flexibility are associated with higher recurrence rates.[6][5][17]

Complications

Complications associated with PHE are rare because the condition usually heals with nonoperative treatment. The most common complication is recurrent pain after throwing. Other potential complications include premature closure of the proximal humeral physis, leading to extremity length discrepancy; osseous remodeling resulting in deformity; and other growth plate anomalies.[6][18][19]

Consultations

Treatment of PHE does not always require consultation with a sports medicine clinician or orthopedic surgeon, provided that the treating clinician is practicing within their scope of expertise and is confident in the diagnosis.

Deterrence and Patient Education

Deterrence of PHE is based on preventing overuse and recurrence. No medications, braces, or injections can prevent injury. Effective prevention focuses on educating athletes, parents, coaches, and trainers that PHE is a growth plate overuse injury caused by repetitive throwing in a skeletally immature shoulder. Continued throwing through pain increases the likelihood of persistent symptoms and recurrence. Workload control, rest, and early symptom recognition are at the core of a strong prevention program.[20]

Several educational points for patients and families should be emphasized:

• Pain while throwing is not normal and should not be ignored: Athletes need to report shoulder pain early, especially pain occurring during late cocking or acceleration, loss of velocity, loss of control, shoulder fatigue, or pain that lingers after throwing. Clinicians should also explain that pain improvement after a few days does not mean the injury has healed.[5][6]
• Throwing-load control is important: Families and patients should be instructed to follow age-appropriate pitch-count and rest recommendations, rest when fatigued, and avoid situations in which total throwing exposure is difficult to monitor, such as concurrent participation in multiple teams or private events.[20][21]
• Total arm load should also be monitored: Catching, long toss, bullpen work, weighted-ball programs, showcases, and high-volume practice throws all contribute to cumulative stress, even though they may not always be captured in total pitch counts.[22]
• Year-round single-sport specialization should be avoided in growing athletes: Baseball specialization is linked to upper-extremity overuse injuries. Patients should be encouraged to participate in other sports during the year and maintain planned periods away from competitive throwing.[23]
• Treatment means stopping throwing until symptoms resolve and function is restored: Athletes should not try to play through this injury. Clinicians should emphasize to patients and families that premature return increases the risk of recurrent pain.[6]
• Patient education should address throwing mechanics and whole-body conditioning: The goal is not just to eliminate symptoms, but also to correct modifiable contributors such as poor warm-up habits, limited shoulder motion, inadequate scapular control, poor trunk and lower-extremity mechanics, and return to pitching before strength and motion have normalized.[13][20]

Pearls and Other Issues

Pearls regarding humeral epiphsiolysis include:

• Proximal humeral epiphysiolysis is related to excess repetitive throwing with inadequate recovery time and is typically seen in youth baseball pitchers aged 11 to 16 years.
• Prevention includes optimizing throwing mechanics, limiting pitch counts, and taking adequate time off from throwing. Time away from throwing includes adequate rest between pitching episodes during the season and 1 season each year completely away from throwing.
• Patients present with nonfocal shoulder pain while throwing and tenderness to palpation over the lateral aspect of the humerus. Muscle weakness and limited range of motion can also be found.
• The radiographic finding indicative of Little League shoulder is widening of the proximal humeral physis.
• Treatment is rest from throwing for 3 to 6 months. Once pain has resolved, core and rotator cuff strengthening exercises are recommended, followed by a gradual return to throwing.

Enhancing Healthcare Team Outcomes

Patients with PHE require a coordinated interprofessional approach. Clinicians must be skilled in recognizing the typical presentation of throwing-related shoulder pain in a skeletally immature athlete while ruling out fracture, infection, instability, labral pathology, and malignant neoplasm. Patient-centered care improves when team responsibilities are explicit. Clinicians confirm the diagnosis, clearly document activity restrictions, interpret imaging, counsel the patient and parents, and determine whether referral to pediatric sports medicine, orthopedic surgery, or physical therapy is appropriate. Nurses reinforce teaching and serve as a source of continuity between visits. Physical therapists and athletic trainers address a range of motion deficits, posterior shoulder tightness, scapular control, kinetic chain weakness, and supervised return-to-throwing progression. Radiologists distinguish subtle physeal widening from alternative pathology.[5][20]

The child's long-term shoulder health should be prioritized over short-term competitive pressure. Shared decision-making should include the athlete and parents, with a clear discussion that PHE is a growth-plate injury, that early return increases the risk of recurrence, and that year-round throwing, participation on multiple teams, and excessive pitch volume can undermine healing. Care coordination is strongest when the team also addresses the athlete's environment by reviewing pitch-count logs, required rest periods, seasonal throwing shutdowns, and workload tracking across teams. Coordinated interprofessional care reduces mixed messages, prevents premature return, improves safety, and enhances care team performance.[6][21]

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Disclosure: Angela Collins declares no relevant financial relationships with ineligible companies.

Disclosure: Todd May declares no relevant financial relationships with ineligible companies.