Little League Shoulder

Little League shoulder (proximal humeral epiphysiolysis) is an overuse injury of the proximal humeral growth plate in skeletally immature throwing athletes. It is essentially a Salter-Harris Type I stress fracture of the proximal humeral physis, produced by repetitive rotational shear and distraction. The physis is the weak link in the young athlete's kinetic chain, and rapid growth spurts increase susceptibility as the physis widens and weakens.

The rule. Shoulder pain in a skeletally immature thrower is Little League shoulder until proven otherwise. Rotator cuff pathology is extremely rare in this age group, so do not diagnose a "strain" without radiographs.

Who. The largest series (Heyworth et al. 2016, n=95) describes the patient: mean age 13.1 years (range 8-16) with an open proximal humeral physis, and strongly male-predominant (93 of 95) but not exclusive to males. 97% were baseball players (86% pitchers, 8% catchers) and about 3% tennis players; the injury is also reported in other overhead athletes (volleyball, cricket). Glenohumeral internal rotation deficit (GIRD) was present in about 30%.

Trend. The condition is diagnosed with increasing frequency, attributed to early sport specialisation and year-round play (Ina et al. 2026; Heyworth et al. 2016). The modifiable risk factors to ask about are:

• High pitch counts exceeding recommended limits
• Intensity: throwing hard, at high velocity, is the real driver, which is why breaking balls (thrown by the harder throwers) are a confounded marker rather than the cause
• Poor technique: opening early, arm lagging, poor mechanics
• Chronicity: playing year-round with no off-season
• Weighted-ball training started prematurely

Development of the proximal humerus. Three ossification centres appear in turn and merge at 5-7 years into a single epiphysis. The physis typically closes at 14-17 years in females and 16-19 years in males, and it contributes 80% of humeral length.

• Head: appears at 6 months
• Greater tuberosity: appears at 3 years
• Lesser tuberosity: appears at 5 years

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Mechanics of injury. In the late cocking phase, maximal external rotation places rotational shear stress across the physis; in the deceleration phase, distraction forces pull on the epiphysis. The physis is weaker against shear and tension than against compression, and the mechanism is repetitive overhead throwing generating high rotational torque at the physis (Sabick et al. 2005). Repeated microtrauma widens the hypertrophic zone of the physis, calcification fails, and a stress fracture eventually follows.

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The kinetic chain. A pitcher who "opens up early" (anterior trunk rotation) leaves the arm lagging behind, and the torque on the physis rises beyond its limits. Biomechanical analysis often reveals a pitcher who relies too much on the arm and not enough on the legs and trunk, the "arm thrower". Poor trunk rotation, scapular dyskinesis or core weakness often predisposes to shoulder overload, which is why rehabilitation must address the entire chain.

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Blood supply. The proximal humeral epiphysis is supplied by the arcuate artery, the ascending branch of the anterior humeral circumflex artery, and the physis acts as a barrier to blood flow from the metaphysis. Damage to the physis could in theory disrupt that supply, but avascular necrosis is extremely rare in Little League shoulder because the fracture is usually a Type I slip without significant displacement or vessel disruption.

Adaptation: humeral retrotorsion. Throwers normally develop increased humeral retroversion, a bony adaptation in which the proximal humerus "twists" during growth to let the hand reach further back in late cocking. The result is increased external rotation and decreased internal rotation, with the total arc of motion (external plus internal) remaining equal to the contralateral side; the extra external rotation is gained without checking the capsule.

Clinical grading. The classic grading is by symptoms, and it sets the length of rest. Most patients present at Grade II or III; Grade IV represents completion of an acute Salter-Harris fracture. The diagnosis is primarily clinical, supported by the radiographic findings.

Salter-Harris context. Little League shoulder is a chronic Salter-Harris Type I stress fracture: the line runs through the physis only, the mechanism is slip or shear, and the prognosis is excellent because the blood supply is preserved. Unlike an acute fracture, there is rarely displacement requiring reduction.

History. The typical patient is a young male pitcher aged 11-16 with progressive shoulder pain, a deep ache over the proximal humerus and lateral shoulder. The pain begins only with throwing and progresses to activities of daily living. Ask about volume: high pitch counts, a recent increase in play, or "showcase" events. The patient often reports fatigue or a "dead arm" sensation.

Examination. Inspection is usually normal, with mild atrophy in chronic cases. The hallmark is maximal tenderness over the proximal humeral physis, on the lateral aspect just below the acromion. Strength is often normal, but resisted abduction or rotation is painful.

Range of motion. GIRD is common, and increased external rotation is the adaptive counterpart. Measure internal rotation rather than estimate it: supine, scapula stabilised, arm abducted to 90 degrees, goniometer aligned with the forearm, both sides measured the same way. A side-to-side internal rotation deficit greater than about 20 degrees defines GIRD.

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Special tests.

• Neer and Hawkins: negative, or falsely positive from extensive irritability
• O'Brien's: usually negative
• Scapular dyskinesis: check for winging or dysrhythmia, a predisposing factor

Little League shoulder is one node in a wider spectrum of open-physis overuse injuries in the skeletally immature thrower (Ina et al. 2026). Roughly 13% of children with Little League shoulder have concurrent elbow pain (Heyworth et al. 2016), so the whole arm must be examined end to end: never clear the shoulder and ignore the elbow.

GIRD, scapular dyskinesis and a poor kinetic chain predispose to all of these, so the rehabilitation that protects the shoulder also protects the elbow. Lateral elbow pain, a mechanical block or an effusion should trigger dedicated elbow radiographs to exclude capitellar OCD, which, unlike Little League shoulder, can require surgery and can end a throwing career if missed.

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Radiographs are mandatory. Request an AP in internal and external rotation and an axillary lateral, and always order comparison views of the contralateral shoulder. The widening can be subtle and physiological asymmetry exists, but significant widening suggests pathology. The signs to look for:

1. Widening of the proximal humeral physis
2. Sclerosis of the metaphyseal margin
3. Fragmentation or cystic change in the lateral metaphysis
4. Demineralisation
5. Periosteal reaction (rare, implies a healing fracture)

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MRI is usually not necessary if the radiographs are diagnostic. It is indicated when:

• Radiographs are normal but clinical suspicion is high (early stress reaction)
• The presentation is unusual and tumour or infection must be ruled out
• Healing or readiness to return to sport needs assessing (sometimes)

The findings are physeal oedema (high T2 signal), metaphyseal oedema usually extending into the shaft, and periosteal oedema.

CT is rarely indicated; avoid the radiation in children.

Algorithm

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The cornerstone is complete rest. Simply "reducing pitch count" or "playing other positions" is insufficient: continued stress leads to growth arrest. Active treatment supplements the primary treatment, which is time.

Growth arrest is the most feared complication. Continued throwing through pain leads to bar formation, and the result is a shortened humerus or a varus deformity; the shortening is usually well tolerated functionally but cosmetically apparent. It is rare (less than 1%) and reported only rarely in the published series, but it can occur if the warnings are ignored.

Counselling the family. The resultant shortening is usually 1-2 cm if the child is near skeletal maturity. In a young child (e.g. 10-12 years) the shortening can be significant, 5 cm or more.

Standard nonoperative cases follow the nonoperative protocol in the Management section.

If surgery was performed (acute fracture fixation), the timeline is slower than for the stress fracture:

• 0-4 weeks: sling immobilisation, pendulums only
• 3-4 weeks: K-wires removed (if used); active-assisted range of motion starts at 4 weeks
• 6-12 weeks: strengthening phases
• Return to sport: delayed compared with the stress fracture, often 6 months or more

Prognosis with rest and physiotherapy is excellent (Heyworth et al. 2016). Mean time to symptom resolution was 2.6 months and mean time to return to competition 4.2 months; the large majority return. Recurrent symptoms occurred in 7% at a mean of 7.6 months after diagnosis. The key determinant is patient and parent compliance with throwing rest, and GIRD increases recurrence risk, so it should be corrected before return.

Throwing through it. Continued throwing gives a poor return to sport: the pain persists, the symptoms worsen chronically, recurrence risk is high, and growth arrest with the shortening it can bring becomes possible.

Long term. The adaptation of humeral retroversion, a normal throwing adaptation, persists.

Because overuse and fatigue, not pitch type, are the dominant modifiable risks (Olsen et al. 2006; Fleisig et al. 2011), age-based pitch counts with mandatory rest days are the cornerstone of both prevention and safe return. The widely used USA Baseball / MLB Pitch Smart limits are examinable; representative daily maxima are:

The rest-day rule scales with the day's pitch count rather than being fixed. For a 13–14-year-old, for example, roughly: 1–20 pitches need no rest day, 21–35 need one, 36–50 need two, 51–65 need three, and 66 or more need four days off. Additional sport-agnostic principles:

• No pitching on consecutive days in the youngest age groups.
• An annual off-season of roughly four months with no competitive throwing.
• Avoid the dual pitcher–catcher role (it multiplies total throws; Fleisig et al. 2011).
• Do not exceed about 100 innings pitched in a calendar year: exceeding this raised serious-injury risk roughly 3.5-fold (Fleisig et al. 2011).
• Never pitch through arm fatigue or pain, the single strongest behavioural risk factor (Olsen et al. 2006).

Global epidemiology:

• Concentrated in baseball-playing regions (USA, Japan, Latin America, Caribbean, parts of East Asia) where youth pitching volume is high; the largest published cohorts come from US paediatric sports-medicine centres (Heyworth et al. 2016).
• Less common where baseball participation is low, but the same physeal overuse mechanism is seen in other overhead-loading sports: tennis (kick/topspin serve with extreme external rotation), volleyball (spikers/jump servers) and cricket (bowlers, although lumbar spondylolysis is the dominant fast-bowler injury).
• Incidence is reported to be rising, attributed to early single-sport specialisation and year-round play without an off-season (Ina et al. 2026).

Major guidelines and consensus, side by side: