Children’s bones don’t grow by adding length along the whole shaft. They grow from a few thin layers of cartilage tucked near the ends of each bone. These layers, called growth plates, are the reason a child gets taller and the reason a teenager eventually stops. They are also softer than the bone around them, which makes them a weak spot: some childhood injuries are more serious than the same injury would be in an adult.
Where Growth Plates Are and What They Look Like
Doctors call the growth plate the physis, a word you may see on an X-ray or fracture report. It sits near each end of a long bone such as the thigh, shin, or forearm bones, in the stretch between the shaft and the rounded end. Smaller growth zones also sit in the wrist and ankle bones and at spots where tendons attach to bone.1PubMed Central. The acrophysis: a unifying concept for enchondral bone growth and its disorders. I. Normal growth. That’s why growth plate trouble can show up at the heel or the bump below the knee in active kids, not just mid-limb. On an X-ray, an open growth plate looks like a dark line across the bone, because cartilage doesn’t show up the way bone does.
It’s easy to mix the growth plate up with joint cartilage. Joint cartilage lines the bone surface where two bones meet and stays for life. The growth plate is buried a little away from the joint, inside the bone end, and it’s the only one of the two that disappears in adulthood. So pain at a joint in a child isn’t automatically a growth plate problem.
In people and other land animals, a separate knob of bone at the end of the bone keeps the growth plate apart from the joint cartilage.2bioRxiv. Evolution of the growth plate into a spatially separated structure allows bone growth on land That bony cap shields the plate, letting its cells withstand about six times more load before they are damaged.3bioRxiv. Evolution of the growth plate into a spatially separated structure allows bone growth on land The design lets bones keep growing while they carry body weight on land.
How a Growth Plate Makes Bones Longer
The plate’s cartilage cells are arranged in layers like a sandwich.4Folia Histochemica et Cytobiollogica. Morphology and physiology of the epiphyseal growth plate Nearest the bone end is a resting layer of small, quiet cells that act as a reserve.5Folia Histochemica et Cytobiollogica. Morphology and physiology of the epiphyseal growth plate Below it, cells divide quickly and stack into neat columns, like coins in a pile.6Folia Histochemica et Cytobiollogica. Morphology and physiology of the epiphyseal growth plate Further down, cells stop dividing and swell to several times their size.7Folia Histochemica et Cytobiollogica. Morphology and physiology of the epiphyseal growth plate So much of the lengthening comes from cells growing bigger, not only from more cells. These swollen cells are also the most sensitive to body weight pressing on them.8bioRxiv. Evolution of the growth plate into a spatially separated structure allows bone growth on land
The swollen cells lay down a material that begins to harden with minerals, then die.9PubMed Central. The growth plate: a physiologic overview10Folia Histochemica et Cytobiollogica. Morphology and physiology of the epiphyseal growth plate Blood vessels and bone-building cells move into the leftover scaffold and lay bone on it.11PubMed. Endochondral ossification: how cartilage is converted into bone in the developing skeleton New bone therefore forms on the shaft side while new cartilage keeps forming on the other side.12PubMed. Molecular mechanisms of endochondral bone development The plate stays roughly the same thickness while the bone behind it lengthens. Over the years the reserve cells are slowly used up, so the plate can’t keep this up forever.
Speed varies. Growth is fastest in infancy and again in the puberty spurt. Each bone, and each end of a bone, grows at its own rate, and the leg plates near the knee contribute much of the gain in height.
The plate only lengthens the bone. Thickness comes from a separate process on the bone’s outer surface, where new bone is laid down layer by layer. Without it, a longer bone would become a thin, fragile rod, so the two processes have to keep pace.
What Controls the Speed of Growth
Growth hormone acts directly on growth plates to boost growth.13PubMed. Insulin-Like Growth Factor-Independent Effects of Growth Hormone on Growth Plate Chondrogenesis and Longitudinal Bone Growth It works largely through a partner hormone, IGF-1, but can also act without it.14PubMed. Insulin-Like Growth Factor-Independent Effects of Growth Hormone on Growth Plate Chondrogenesis and Longitudinal Bone Growth In puberty, estrogen, present in both boys and girls, raises growth hormone and drives the growth spurt.15PubMed Central. Pubertal growth and epiphyseal fusion
Cells inside the plate also send chemical messages back and forth that decide how fast cells divide and when they swell.16Pediatric Research. Developmental Pathways in Musculoskeletal Neoplasia: Involvement of the Indian Hedgehog-Parathyroid Hormone-Related Protein Pathway This feedback loop keeps the columns orderly and growth steady.17PubMed Central. Organization of the Indian hedgehog – parathyroid hormone-related protein system in the postnatal growth plate
Long-term illness and stress hormones such as cortisol slow the growth plate.18PubMed. The effect of acute and chronic stress on growth Inflammation chemicals reduce cell division and blunt IGF-1’s effect on the plate.19PubMed Central. Chronic inflammation and the growth hormone/insulin-like growth factor-1 axis So steroid medicines and chronic inflammatory diseases, like bowel inflammation, can slow a child’s growth. Doctors focus on treating the illness and keeping steroid doses low.
Growth also needs fuel. Plates can only respond to growth hormone if the child gets enough overall calories and protein, since growth is one of the first things the body trims when supply is short. Long-term undernutrition therefore slows height gain even when hormone levels are normal. Thyroid hormone is another everyday regulator: a child whose thyroid is underactive can grow slowly, and treatment usually brings growth back toward its track.
Growth hormone treatment only works while growth plates are open. It is prescribed for proven deficiency or certain conditions, not for average height, and doctors check bone age before deciding.
When Growth Plates Close
Growth plates age on a built-in schedule, with cells dividing less over time.20PubMed Central. Effects of estrogen on growth plate senescence and epiphyseal fusion Closure, also called fusion, happens fast once cell division nearly stops: the remaining cartilage is quickly replaced by bone.21PubMed Central. Effects of estrogen on growth plate senescence and epiphyseal fusion Estrogen speeds up that aging rather than turning cartilage to bone directly.22PubMed Central. Effects of estrogen on growth plate senescence and epiphyseal fusion Low estrogen early in puberty fuels the spurt, while higher levels late in puberty bring closure.23PubMed Central. Pubertal growth and epiphyseal fusion This applies to boys too, since their bodies make estrogen from testosterone.
Most plates close roughly between 14 and 16 in girls and 16 and 19 in boys. Plates in different bones close at different times, and some not until the early 20s. Early puberty often means plates close earlier, so growth ends sooner.
Girls usually start puberty earlier, so their plates reach the high estrogen levels that bring closure sooner. Boys’ growth spurt comes later and runs longer, which gives them more total growing time and usually more adult height.
To see how much growing is left, doctors estimate bone age, which is how mature the skeleton looks, from an X-ray of the left hand and wrist.24PubMed Central. Bone age: assessment methods and clinical applications The hand has many bones and is easy to X-ray.25PubMed Central. Bone age: assessment methods and clinical applications MRI of the wrist growth plate gives similar results without radiation, and it’s used in some sports age checks.26PubMed. Comparison study of growth plate fusion using MRI versus plain radiographs as used in age determination for exclusion of overaged football players
A bone age younger than real age suggests more growing time left, and an older one suggests less. It helps predict adult height but has a margin of error.
Once plates close, height from bone length stops. Posture or spine changes may shift measured height slightly, but supplements and stretching cannot reopen plates.
Growth Plate Injuries and Why They Matter
Doctors grade growth plate fractures by Salter-Harris type, from I to V, which may appear on reports. The biggest risks are breaks that cross the cell-dividing layer, types III and IV.27Surgery. Physeal injuries in children High-energy crush injuries, type V, also often stop growth.28Surgery. Physeal injuries in children Inner-ankle fractures of types III and IV have a high rate of early closure.29PubMed. Prognostic factors for premature growth plate arrest as a complication of the surgical treatment of fractures of the medial malleolus in children A bridge of bone can form across the plate, stopping or tilting growth.
In a growing child the plate is softer than the bone and the ligaments around it, so force that would sprain a ligament in an adult can instead injure the plate. Doctors therefore treat a child’s possible plate injury as a fracture until imaging shows otherwise. The worry is less about the pain or the break healing and more about whether that plate keeps growing normally afterward.
Signs to look for include pain near the end of a bone rather than a joint ache, swelling, tenderness, or refusing to use the limb. Seek care rather than waiting to see if it settles.
Cartilage doesn’t show well on X-ray, so MRI can show injuries X-rays miss.30PubMed. MRI of pediatric growth plate injury: correlation with plain film radiographs and clinical outcome MRI can also track the plate’s condition and help predict limb deformity.31PubMed. Status of growth plates can be monitored by MRI Keep follow-up visits for months after healing, even if the child feels fine. Follow-up usually means repeat X-rays that compare both limbs, with doctors watching for length differences or angling. Early bone bridges can sometimes be treated surgically.
Scientists are testing engineered cartilage and scaffolds to repair damaged plates.32PubMed Central. Advances in tissue engineering for the repair of growth plate injuries In animals, these regrow cartilage, but its structure is disorganized.33PubMed. Treatment of growth plate injury using IGF-I-loaded PLGA scaffolds 3D-printed scaffolds reduced bone bridges and limb deformity in animals.34PubMed Central. 3D bioprinted hydrogel/polymer scaffold with factor delivery and mechanical support for growth plate injury repair These approaches are not yet standard treatment.
Sports, Weight and Pressure on Growth Plates
Steady extra pressure on a growth plate slows its growth, while less pressure speeds it.35PubMed Central. Growth Plate Mechanics and Mechanobiology. A Survey of Present Understanding Sustained compression of normal strength can cut growth by 40% or more, while pulling forces raise it only a little.36PubMed. Mechanical effects on skeletal growth This only holds within a normal range; very high pressure damages the plate.37PubMed Central. The true history of the Hueter-Volkmann law
Normal running, jumping, and play load the plate within its usual range, and a child’s bones respond by becoming stronger. The concern is a very different situation: repeated heavy loading, as in some intensive training, with too little recovery.
Ordinary play and sport help bone health. Year-round single-sport overuse without rest is worth avoiding, while supervised strength training with good form is considered fine. Persistent pain at a bone end means rest and evaluation.
Higher body weight raises the chance that the hip growth plate slips, a condition called slipped capital femoral epiphysis.38PubMed Central. A damage model for the growth plate: application to the prediction of slipped capital epiphysis A steeper tilt of the plate raises the risk too.39PubMed Central. A damage model for the growth plate: application to the prediction of slipped capital epiphysis A teen with a limp or knee or groin pain should be checked promptly.
Conditions That Affect Growth Plates
Achondroplasia, the most common cause of short-limbed dwarfism, comes from one change in a gene called FGFR3.40PubMed. Fibroblast growth factor receptor-3 as a therapeutic target for Achondroplasia–genetic short limbed dwarfism The change makes a growth brake signal overactive, slowing growth plate cell division.41PubMed Central. Knock-in human FGFR3 achondroplasia mutation as a mouse model for human skeletal dysplasia It disrupts both cell division and maturing, which delays bone age.42PubMed. Delayed bone age due to a dual effect of FGFR3 mutation in Achondroplasia
Rickets is poor hardening of bone at the growth plate, slowing growth.43BMJ Best Practice. Rickets Untreated, it causes bowed legs and thickened bone ends.44BMJ Best Practice. Rickets It most often comes from too little vitamin D, sometimes calcium or phosphorus.45BMJ Best Practice. Rickets That’s why it’s worth asking about vitamin D for breastfed babies and children with little sun. Growth concerns worth raising include a child falling across growth chart lines, bowed legs that worsen after age two, or limbs that look out of proportion to the trunk.
Rickets usually responds to vitamin D and calcium. Newer medicines for achondroplasia target the overactive signal. Both work only while plates are open.