How tissue heals, and what regenerative therapy can offer
An ankle stops hurting at three weeks and gives way at nine, on flat ground, doing nothing dramatic. Nothing was missed on the scan. The part still under construction is the part that cannot be seen.
An ankle sprain stops hurting after about three weeks. The swelling is gone, walking is normal, a slow jog feels fine. Six weeks later the same ankle gives way on flat ground, doing nothing dramatic. Nothing was missed on any scan. The tissue was simply not finished, and the part still under construction is invisible.
By the end of this piece you will know the sequence tissue follows when it repairs, the three things it needs, and where regenerative treatments stand on the evidence ladder.
Why is inflammation the repair, not the problem?
Within seconds of an injury, tiny blood fragments called platelets plug the gap. They also release a burst of growth factors, the chemical messages that tell cells to start repairing. That clot is not only a stopper. It is the first scaffold and the first set of instructions.
Immune cells arrive within hours and clear the site of debris and dead cells. Then comes the part worth knowing. The clean-up cells change character. Cells that arrived to destroy switch roles and start directing the rebuild, calling in builder cells and new blood vessels. Inflammation is not the obstacle to healing but the first stage of it, and the same cells that cause the swelling later run the reconstruction.
That makes the instinct to shut down inflammation as fast as possible less obviously right than it feels. Whether strong early suppression slows tendon or bone healing in people is still being studied. The mechanism is clear, the data mixed. What is not in doubt is that clearing comes before building.
Why does recovery feel finished long before it is?
From roughly day three, builder cells called fibroblasts move into the clot. They lay down collagen, the rope-like protein that gives tissue its strength. The first collagen is a quick, disorganised type: present, but mechanically poor. New small blood vessels sprout behind it. Over about three weeks the gap closes, swelling settles and pain fades. This is where almost everyone declares the injury healed.
Then remodelling begins: slow, silent and long. The quick collagen is gradually replaced by a stronger type. Fibres line up along the lines of load instead of lying at random. Strength climbs in small steps over months. The visible part of healing ends in weeks, while the phase that decides the tissue’s final strength runs for months. Repaired tissue also rarely returns to its original specification.
At the moment pain disappears, how much of its final strength has the tissue recovered? Far less than it feels. Pain settles with inflammation, not with the maturity of the new tissue, and the two are months apart. That mismatch is why re-injury clusters just after someone feels better. It is also why remodelling is the phase people abandon: none of it is visible or feels like progress.
Remodelling explains the timescale. It does not yet explain what decides whether the rebuild ends well.
What are the three things every repair needs?
Strip away the branding and every repair depends on the same three inputs. The first is a signal: growth factors and chemical messengers instructing cells to arrive, divide and build. Mechanical load is a signal too, because tension along a healing tendon tells the builder cells which way to lay collagen.
The second is a scaffold: something for cells to crawl along and build into. If the gap is too wide, or movement keeps tearing the bridge apart, nothing else proceeds. The third is supply plus time. Oxygen, nutrients and cells arrive through blood, every step is expensive, and none of it hurries.
Almost every credible regenerative treatment is an attempt to supply one of those three, rather than to create tissue from nothing. Injections that concentrate growth factors supply signal. Grafts and matrix materials supply scaffold. Rehabilitation that loads tissue for months supplies the right signal over time. Ozone, dosed as a controlled stimulus, sits in the signal family too.
The useful question about any regenerative treatment is which of the three it supplies, and whether the target tissue can use it. A signal delivered into tissue with no blood supply and no dividing cells has nowhere to go.
That question also predicts, before any trial, which tissues will be hard.
Why do cartilage, tendon and disc heal badly?
Skin, muscle, bone and the gut lining share two features: generous blood supply and cells that divide readily. Bone is the standout. It heals close to its original architecture rather than as scar.
Now the difficult end. The smooth cartilage inside joints has no blood supply at all. Its cells are sparse, rarely divide, and are fed by slow seepage from the joint fluid. The middle of a tendon has a thin blood supply and few, slow cells, so it repairs through scar over months to years. The discs between the bones of the spine are the largest structures in the body without their own blood supply, and the seepage that feeds them falls with age.
Blood supply and cell turnover predict which tissues heal well, which is why cartilage, tendon and disc are the hard cases for every therapy. That ceiling is why the same treatment can help clearly in one condition and less in another.
Where does the evidence stand today?
Start with the treatment nobody advertises. Progressive loading, structured rehabilitation and enough time have the strongest and most consistent randomised evidence in tendon problems and knee osteoarthritis. Everything injected works with that foundation, not instead of it.
Platelet-rich plasma, or PRP, concentrates a person’s own platelets and returns them to the injured site as a rich dose of signal. Early results in knee osteoarthritis and some tendon problems are promising. Trials differ in how the product is prepared, what platelet concentration is used and how many sessions are given. So researchers are now working out which preparations suit which problems, and that research is in motion.
Cell-based injections use a person’s own bone marrow or fat. The most likely way they help is by signalling to local cells, rather than by turning into new tissue themselves. These treatments are being studied, with early trials small so far and larger controlled trials under way. Prolotherapy injects a mild irritant, such as a dextrose solution, to wake a fresh repair response. Its small trials lean positive, which makes the early evidence promising. The practical guidance is simple: choose a practitioner who explains what is in the syringe, how it was prepared, and how it fits your loading programme.
Proven: progressive loading and exercise-based rehabilitation for tendon problems and knee osteoarthritis, supported by randomised trials and consistent across them. Promising: platelet-rich plasma for knee osteoarthritis and selected tendon problems, and prolotherapy in small positive trials. Being studied: cell-based injections, where the signalling mechanism is plausible and larger trials are in progress. No current treatment rebuilds adult joint cartilage to its original tissue, which is why protecting what remains matters so much. Which option suits a particular person is a decision for them and their own clinician.
- Inflammation is the opening phase of repair, not an interruption to it.
- Pain settles with inflammation; strength arrives with remodelling, months later.
- Tissue needs a signal, a scaffold, and supply plus time. Credible therapies supply one of them.
- Blood supply and cell turnover set the ceiling: cartilage, tendon and disc are hard for every therapy.
- Injected treatments work best alongside graded loading over months, never instead of it.
Signal, scaffold and supply is the grammar underneath every therapy in this field. The knowledge check will show how steadily it holds once the labels come off.
