Veteran All Black Israel Dagg has used stem cell therapy on his damaged knee cartilage as he attempts to revive a long test career which hangs in the balance.

Hundreds of NFL players are among the athletes who have used the radical treatment, which also appears to have saved tennis star Rafael Nadal's career.

Outside back Dagg made his comeback in the Crusaders surprisingly tough 33-11 win over the Sunwolves, after he had two warm-up games for the University club, Stuff reported.

Dagg has been sidelined for seven months, since the All Blacks played Argentina when he scored a clever try in New Plymouth to underline that he could still be a test force.

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Dagg is only 29 but the rise of brilliant outside backs such as Rieko Ioane and Jordie Barrett, plus his own injury battle, leaves Dagg as probably an outside prospect for next year's World Cup.

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He had a tough re-introduction to top level rugby, getting few opportunities on the left wing in rough weather conditions in Christchurch on Saturday night.

The jury remains out, including on the injury and the effectiveness of stem cell therapy.

Some research says that it is unlikely to provide enough cartilage to correct a "bone on bone" situation, although it is anti-inflammatory and could at least provide pain relief.

Israel Dagg got few opportunities against the Sunwolves. Photo / Photosport
Israel Dagg got few opportunities against the Sunwolves. Photo / Photosport

Dagg said the injury was "knock knee" which means the joint is at an unusual angle. He had stem cells injected into the right knee at a Queenstown clinic.

"I have got no cartilage in my knee, so every time I jump it is just bone on bone; it just bruises, releases fluid," Dagg said.

"It would be alright if I just had to trundle around, but I have got to be explosive. But I am through it now, I am on the other side. I have just got to keep positive and deal with the new normal. I am not my old self, but I can still play footy. That is the main thing.

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"Hopefully that (stem cell treatment) works, and apparently it regenerates cartilage and that is what I need. I need cartilage in between my bones, because pretty much it is just bone on bone."

He has to ensure that the way he runs doesn't aggravate the problem.

Dagg said: "It is like starting to walk again. You have got to train yourself to use the same power out of each leg and things like that. It was a bit of a learning curve but I am just happy to be throwing the ball around again."

Nadal is among the sports people who have used stem cell therapy - the Spaniard had fat and bone marrow cells injected to treat his back issues in 2014. He has since risen back to the top of world tennis.

Even the 82-year-old Indianapolis 5000 legend A.J.Foyt had the therapy, on ankle and shoulder problems. But the procedure is considered so alternative that NFL teams for instance don't pay the medical costs, according to one Sports Illustrated report three years ago.

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