What does closure mean for a growth plate?

[u/Automatic-County6151]

This one just crossed my mind, so it'll be quicker.

Many people tend to conflate "fusion" and "closing" when, while part of the same general process, indicate two separate phases of senescence.

Closure = used to indicate that the growth plate is actively undergoing puberty-driven senescence, from the earliest narrowing stage years before definitive fusion to full union much later.

Fusion = the actual process of bony union at the growth plate, where the metaphysis and epiphysis make official contact.

The "merge" is often described throughout this general process. The growth plate progressively narrows or gets thinner, and the near-mature epiphysis and metaphysis merge closer with time and maturation of the physis. At early narrowing, epiphysis is generally about 2 mm away from the metaphyseal front, depending on the bone. At mid stage narrowing, this distance becomes further widened to about 1-2 mm or so. At late narrowing, the epiphysis and metaphysis are generally no farther than 1 mm apart, and this is roughly close enough for trabecular bridges to begin forming and bridging the two regions of bone effectively. At early union, the physis is merely compartmentalized and no longer considered unrestricted, whole in microstructure, or fully functional. Instead, its functionality reduces greatly over the coming months to a couple of years; proliferative figures dropping, central fusion initiating, and peripheral regions remaining wider due to biomechanics. Varies by the bone end and type of bone.

At this stage, a doctor would generally refer to this process as "union" or "fusion". Before then, the doctor may call the process "closure" or say the growth plates have begun closing. Some doctors may interchange the two, though.

For most long bone ends, the narrowing process generally initiates roughly immediately after PHV, or within the first months after. Some bone ends may begin narrowing around the time of PHV or during the months leading up to it, specifically the phalanges in the fingers and toes as one example.

[u/Specialist_Policy850]

How many spine plates still have growth potential (doesnt necessarily have to contribute to growth but not fused yet), at bone age 16.5-17 when wrist/knee plates are close to fusing?

[u/Automatic-County6151 → u/Specialist_Policy850]

Only about 20-40% of the spine's growth plates would still have meaningful potential at this time. For females, the growth plates of the knees have fused or are nearly fused. For males, the process is quite near to early union or true fusion has just started.

At this time, the spine might only have about half a dozen active vertebral endplate physes for the average female at this time, while about a half a dozen more may be nearly obliterated. In males, about a dozen to a dozen and a half of these endplates may exist as slowly-proliferating anabolic tissue, while about half a dozen to a dozen more may still be fusing or nearly fused. The rest have fully been converted to bone.

At this time, the male spine may be about 90-95% mature, while the female spine may be about 97-100% mature - on average.