What a growth plate actually is
A growth plate, or physis, is a layer of cartilage near the end of a long bone where new bone is laid down. While it remains open, the bone can lengthen. When growth finishes, the cartilage is replaced by bone and the plate 'closes' or fuses, after which that bone cannot get any longer.
There is a second type worth knowing: the apophysis. This is a growth area where a tendon attaches, rather than one that adds length. The tibial tuberosity below the kneecap, the calcaneal apophysis at the back of the heel and the lower pole of the patella are all apophyses, and they are the sites involved in Osgood-Schlatter, Sever's disease and Sinding-Larsen-Johansson respectively.
Physis (growth plate)
- Adds length to the bone
- Sits near the ends of long bones
- Closure ends height growth in that bone
- Relevant to fracture risk in youth
Apophysis (traction site)
- Where a tendon attaches to bone
- Knee, heel, hip, elbow
- Sensitive to repeated pull during growth
- Site of the common growth-related conditions
Typical closure ages
Closure happens bone by bone rather than all at once, and consistently earlier in girls than boys, a difference of roughly two years on average. The figures below are typical ranges rather than deadlines; individual variation of two years either side is entirely normal.
| Site | Girls (typical) | Boys (typical) | Associated condition |
|---|---|---|---|
| Calcaneal apophysis (heel) | 12-14 | 14-16 | Sever's disease |
| Tibial tuberosity (knee) | 13-15 | 15-17 | Osgood-Schlatter |
| Lower pole of patella | 12-14 | 14-16 | Sinding-Larsen-Johansson |
| Distal femur / proximal tibia | 14-16 | 16-18 | Long bone length |
| Iliac crest / pelvic apophyses | 14-16 | 16-18 | Hip and groin traction pain |
| Spine ring apophyses | 15-17 | 17-19 | Growth-related back pain |
Ranges are approximate. Maturity timing shifts every row by a year or two in both directions.
Why the window before closure matters
During the years leading up to closure, the growth area is the mechanically weakest link in the chain. Bone lengthens quickly, the muscle-tendon unit crossing the joint is pulled tighter, and the attachment site absorbs repeated traction from sprinting, jumping and kicking. The result is the familiar pattern of activity-related pain at the knee or heel in an otherwise healthy, active young athlete.
It also changes what an injury looks like. In an adult the tendon or ligament often fails first; in a growing athlete the growth area is more likely to be the site of complaint, which is why persistent bony point tenderness in a young athlete deserves a proper assessment rather than a stretching routine.
Phase 1
Pre-spurt
Plates wide open, growth steady, tolerance generally good. Ideal time to build movement skill and bodyweight strength.
Phase 2
Rapid growth
Fastest lengthening, tightest soft tissue, highest rate of apophyseal symptoms. Hold volume, reduce impact repetition, keep strength work in.
Phase 3
Approaching closure
Growth velocity slows, symptoms typically start settling, capacity for strength and power work rises quickly.
Phase 4
Closed
Growth-plate pain resolves at that site. A visible bony lump at the knee may remain permanently and is usually harmless.
Does pain always stop at closure?
For apophyseal conditions, symptoms usually settle as the growth area fuses, that is one of the reasons these conditions are described as self-limiting. It is a genuine reassurance, but it is not a reason to wait it out passively. The months of reduced training, lost fitness and lost confidence matter, and they can be substantially reduced with sensible load management and strength work.
A minority of athletes have residual symptoms after closure, most often at the knee where a prominent tibial tuberosity can be tender when kneeling. That is worth assessing rather than assuming it will disappear.
What this means for training
- Do not stop training in the growth window, modify the ingredients instead.
- Reduce repeated high-impact volume, particularly jump landings and hard running on unforgiving surfaces.
- Keep progressive strength work going; it is well tolerated at this stage and protects capacity.
- Use symptoms during and 24 hours after activity as the guide to whether the dose was right.
- Expect gradual improvement over weeks rather than a fix in days.
When to get it checked
Seek an assessment if
Pain wakes the athlete at night, appears without activity, comes with swelling, redness or fever, follows a single traumatic incident, or persists beyond a few weeks despite reducing load. These features do not fit a routine growth-related picture.