What it is
The bony bump on the inside of the elbow (the medial epicondyle) has its own growth centre, which appears at about 6 to 7 years old and usually fuses by about 15, though it can stay open until about 17. The forearm muscles that grip, and the elbow's inner ligament, attach to it. Each throw bends the elbow outwards with large forces as the arm comes forward.
In a growing child the growth cartilage is weaker than the ligament and tendons pulling on it, so the repeated pull falls on the growth plate. It gets irritated and can widen, and in the severe form the bump pulls off (an avulsion fracture). Once the growth plate has fused, the same forces fall on the ligament instead. That is why ligament reconstructions (Tommy John surgery) peak at 15 to 19: they made up 56.8% of these operations in one US insurance database.
Sources 1, 2, 3, 4, 5, 6, 7
Who gets it
It mostly affects boys aged about 8 to 15 who pitch, but also catchers, infielders and outfielders who throw a lot, and young players in softball, tennis, water polo and volleyball. In 317 children seen over 15 years at one children's hospital, the average age was 12.8, 98% were boys and 98% played baseball; the rest included a few tennis players and American football quarterbacks.
Arm pain is common in young pitchers: in 476 pitchers aged 9 to 14 followed for a season, half had elbow or shoulder pain. In Japanese surveys, 9.0% of youth players reported an elbow injury in a season in 2021, down from 19.1% in 2011 after rule changes.
Sources 4, 5, 8, 9, 10
What raises the risk: the list for parents and coaches
The biggest factors are the amount of throwing and too little recovery, above all pitching with a tired or sore arm. In studies of young pitchers, the risk went up with more pitches per game and per season; pitching on consecutive days, for several teams with overlapping seasons, or in several games a day; more months a year, more showcases and faster pitching; more than 100 innings a year; training more than 16 hours a week; and earlier elbow pain. On magnetic resonance imaging (MRI) before a season, 47% of players who played all year had elbow changes, against 11% of the others. Catchers make a lot of throws too, and had the most changes at the growth centre in one X-ray study.
Pitch type is debated. Sliders went with more elbow pain in one study and curveballs with more arm pain in a survey, but curveballs before 13 weren't linked with serious injury over 10 years. Pitch Smart, the youth pitching guidelines from Major League Baseball and USA Baseball, advises fastballs and changeups first and breaking pitches from 13. A throwing shoulder that is stiffer turning inwards was found in 55% of the children examined in one series, and went with a slower recovery.
Sources 10, 11, 12, 13, 14, 15, 16, 17, 8
How it's recognised
Pain on the inner elbow that builds gradually, at first only when pitching and later with any throwing, with tenderness on the bump, sometimes swelling or lost elbow movement, and slower or less accurate throws. Occasionally it starts with a painful pop. Young athletes often play down their symptoms to keep playing.
A doctor or physiotherapist diagnoses it from the story and an examination of the elbow and the shoulder. Pain on the outer side of the elbow, locking or catching points to a different problem, such as a loose fragment or damage to the joint surface.
Sources 4, 5, 18, 3, 2
What X-rays and scans do and don't meanEmerging evidence
X-rays of both elbows, so they can be compared, are usual at the first visit. They show whether the growth plate is open, and can show widening, fragments or a bump that has pulled away, though they can also look normal in a child who still has pain. After a pop or sudden severe pain, an X-ray is needed the same day.
Changes are very common in young throwers who feel fine. In 343 Little League players, the growth centre looked enlarged on X-ray in all the pitchers and catchers and 90% of the fielders, and separated in 50% to 70%, yet only about half of those with a separated or broken-up growth centre had any soreness. On MRI, 35% of 26 Little League players without symptoms had inner elbow changes before a season. By the end of a season in which every player kept to the pitching limits, 48% had changes, and 28% had had elbow pain during it; 3 years later 58% had changes, and 27% reported throwing elbow pain. Ultrasound found small flakes pulled off at the ligament's attachment in 36% of 64 throwing elbows without symptoms.
A finding still matters. Changes on ultrasound before a season went with 2.5 times the odds of an elbow injury during it (28.8% against 11.9% of 210 players aged 7 to 12), so in a child who feels fine a scan finding is a reason to look hard at the workload, not a diagnosis on its own. And a normal X-ray doesn't rule an injury out: in 50 boys with inner elbow pain, ultrasound found small avulsions in 78%, and 72% of those had normal X-rays.
Sources 18, 5, 6, 4, 16, 14, 19, 20, 21, 22, 23
Pain on the outer elbow is a different problemEmerging evidence
Pain on the outer side of a young thrower's elbow can come from osteochondritis dissecans (OCD), where throwing squashes and damages the joint surface on that side. On ultrasound screening of primary-school-age players in Japan, 1.4% had it, only about a third of them (34.4%) had ever had elbow pain, and 73% were at the earliest stage. Early, stable lesions in children whose growth plate is still open usually heal with months off throwing (16 of 17 in one series), though healing on X-ray took over a year on average; unstable ones often need surgery. X-rays can miss early lesions, so outer elbow pain needs checking. Our elbow OCD guide covers it.
Sources 24, 2, 40, 41
How it usually goes
Rest usually works. In 268 children with the growth plate form at one hospital, the median return to sport was 12 weeks, with half returning between 7 and 18 weeks. Pain came back in 13%, at a median of 2 years, more often in children who had had symptoms for longer before they were diagnosed, and one child who didn't rest went on to pull the bump off.
Over 5 years in another group of 44 children, 84% returned to competition, 20% changed position, 21% had pain again, and fewer than half were still playing baseball; very few needed arm surgery. Left untreated, it can lead to loose fragments, deformity and early arthritis.
Sources 8, 25, 5, 4
