How to regenerate knee cartilage naturally?

The astronaut and the runner: what happens to knee cartilage when it is unloaded and when it is moderately loaded, and what that proves

How to regenerate knee cartilage naturally is a question that the shelf answers with a tub and the honest page answers with two people, the astronaut and the runner, because between them they show exactly what knee cartilage can and cannot do and the honest answer lives in the space between their cases. Start with what cartilage is. The articular cartilage of the knee is a few millimetres of glassy tissue capping the ends of the thigh bone and shin bone and the back of the kneecap, made of a collagen framework holding a dense mesh of proteoglycans whose glycosaminoglycan chains carry so much negative charge that they draw water into the tissue and swell against the collagen, so that cartilage is around three-quarters water held under pressure, which is what lets it bear the loads of walking and running with almost no friction. It has no blood supply and no nerves, and its cells, the chondrocytes, sit locked in the matrix they made, unable to move; they are fed by the joint fluid, which is squeezed out of the cartilage when it is loaded and drawn back in, carrying nutrients, when the load comes off, so that every step is a pump stroke and a cartilage that is not loaded is a cartilage that is not fed. Now the astronaut. Months without gravity remove the load from the knee, and the cartilage responds as unloaded tissue does: on MRI it thins and its glycosaminoglycan content falls, with the same changes seen within weeks to months in people on prolonged bed rest, in people with spinal cord injury whose legs no longer bear weight, and in a leg that has spent six weeks in a cast after a fracture, and with only partial recovery when loading returns, especially after long unloading. The astronaut's cartilage has not been injured and has not been starved of any nutrient; it has been unloaded, and unloaded cartilage wastes, because the maintenance of the matrix is a response to the load that squeezes the pump and strains the chondrocytes. Now the runner, or more precisely the people in the exercise trials, since the honest page does not claim more than the trials did: in people at risk of knee osteoarthritis, who had had a meniscus operation or carried extra weight, a moderate supervised exercise programme over several months raised the glycosaminoglycan content of their knee cartilage on contrast MRI, the imaging method that measures it, while the comparison group who stayed sedentary saw theirs fall, and the observational imaging in habitual runners finds cartilage no thinner and in some studies compositionally richer than in non-runners. Cartilage reads load the way bone does: it adapts its composition, the glycosaminoglycan and water that let it resist compression, to the load it receives, upward under moderate cyclic load and downward under none. That is the proof, and it cuts both ways. It proves that knee cartilage can be improved naturally, in the sense of restoring composition and function to cartilage that has been unloaded or under-loaded, and the water and glycosaminoglycan account of that improvement is on the increase cartilage naturally page. And it sets the limit, because in none of these studies did adult cartilage grow thicker than it had been or fill a defect, and the honest page turns to that limit next.

What cartilage cannot do, the two meanings of regenerate, the four natural levers and how to dose them, and where supplements sit

What adult knee cartilage cannot do is thicken or regrow a defect, and the reason is the same biology that makes it waste when unloaded: its cells cannot move and nothing can bring new ones. A chondrocyte sits in its lacuna in a matrix it cannot migrate through, so when a patch of cartilage is worn away or gouged out by an injury there are no cells at the edge that can crawl across the defect and lay new tissue, and there is no blood supply to deliver the stem cells or the inflammatory response that would start a repair elsewhere; the defect stays, or fills at best with fibrocartilage, a scar-like tissue that lacks the compressive properties of the original, if it reaches down to the bone and the marrow bleeds into it. That is why cartilage repair is a surgical field, cell implantation, microfracture and grafts for focal defects in the right knees, whose existence is itself the proof that no natural or oral route regrows it, on the knee cartilage repair page, and why the supplement imaging trials, glucosamine, chondroitin, collagen hydrolysate, vitamin D and fish oil measured by MRI and X-ray in knee osteoarthritis, found no regrowth and no meaningful slowing of loss, on the supplements rebuild cartilage page. So regenerate has two meanings and the honest page separates them. Regenerate in the shelf's sense, growing back cartilage that has gone, is not available to an adult by any natural means and by no supplement, and a reader with a worn knee on X-ray is managing the cartilage that remains, not regrowing what has gone. Regenerate in the astronaut's sense, restoring the composition and the function of cartilage that has been unloaded or under-loaded, which is most cartilage in a reader who has been resting a sore knee, is available and the levers are natural. The first lever is moderate cyclic load, and the dose is the word moderate: walking and cycling pump the joint fluid through the cartilage thousands of times an hour without the impact that a sore knee resents, so a reader begins with daily walking and cycling at a volume the knee tolerates with no more than mild pain that settles by the next day, and raises the volume as tolerance grows, with running added later for those whose knees take it and not forced on those whose do not. The second lever is quadriceps strength, because the quadriceps absorbs the load of each step before it reaches the joint surface and a weak quadriceps is one of the strongest predictors of knee osteoarthritis progressing, so leg presses, squats to a tolerable depth, step-ups and straight-leg work, two or three times a week, are cartilage work as much as muscle work. The third lever is body weight, because each kilogram carried adds around four kilograms of load across the knee with every step, so that a reader who loses five kilograms has removed twenty from each stride and some seven million kilograms from a year of walking, which is the single largest lever available to a heavier reader and the one the osteoarthritis guidance puts first. The fourth lever is never being immobilised for longer than an injury requires, since the astronaut's lesson is that weeks of unloading cost cartilage that months of loading only partly buy back, so that a knee after an injury or an operation is moved and loaded as early as the surgeon or physiotherapist allows and a sore knee is walked within tolerance rather than rested until it stops hurting. Where supplements sit is beneath all four: no oral agent has changed knee cartilage on imaging, with one small pilot of collagen hydrolysate reporting a glycosaminoglycan change on contrast MRI in some knee regions that has not been replicated, the joint questionnaire trials at around 10g a day reporting a point or two less pain with no cartilage change on the scans that looked, and the astronaut's cartilage recovering by walking and not by eating. The worked example is the adjunct with no cartilage imaging result, stated on its true terms: two capsules, 1200mg hydrolysed type 1 marine collagen with 12mg vitamin C at 15% of its reference value plus zinc, 120 for £16.99 at 28p a day, lab tested and UK made, below the 10g joint trial dose, carrying vitamin C's collagen formation sentence for the normal function of cartilage and no cartilage claim of its own. How to regenerate knee cartilage naturally: not in the shelf's sense, and in the astronaut's sense by walking, cycling, a strong quadriceps, a lighter body and no cast a day longer than needed.

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