Radiocarbon dating shows adult cartilage collagen is almost never replaced

What they did

The bomb-pulse method uses the spike in atmospheric carbon-14 caused by nuclear tests: a tissue records the carbon-14 level present when it was made. The researchers measured carbon-14 in collagen from tibial plateau cartilage (the top of the shin bone inside the knee) from 23 people born between 1935 and 1997, 15 with osteoarthritis and 8 with healthy cartilage, and compared regions across the joint surface.

What they found

Carbon-14 levels showed that virtually no replacement of the collagen matrix happened after skeletal maturity. Neither osteoarthritis nor tissue damage changed collagen turnover. Collagen in the centre of the joint surface was formed several years earlier than collagen at the edges. The authors conclude that the collagen matrix of adult human articular cartilage is an essentially permanent structure with no significant turnover, even with disease.

What it can't tell us

Twenty-three people, from one site in the knee, is a small sample. The study measured collagen only, not aggrecan or the other parts of cartilage, and it tested no treatment, so it cannot say whether anything changes turnover.

Why it matters

It confirms with a different method what Verzijl's 117-year half-life suggested: the collagen in adult cartilage is essentially the collagen laid down by the time the skeleton stopped growing. Type II collagen that MMP13 cuts is not replaced, which is why research focuses on protecting what is there.

The paper

1. Heinemeier KM, Schjerling P, Heinemeier J et al. Radiocarbon dating reveals minimal collagen turnover in both healthy and osteoarthritic human cartilage. Sci Transl Med 2016.
   PMID 27384346DOI 10.1126/scitranslmed.aad8335

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