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Sounds like this person had an injury, didn't treat it, and it got worse. It seems like a pretty huge, unsubstantiated leap to claim that running "causes significant health problems".

Supplemental strength training (see anatomy for runners) and carefully ramping up mileage.

Except you still don't know what's the matter with his knee, and you definitely don't know what caused it. It seems a bit premature to assume that overtraining was the cause, and it's pretty ridiculous to imply that because some runners have hurt their knees, it is unsafe, or pointless.