Just a reality check....my dad played soccer for 50 years and had about 3 or 4 knee surgeries where they removed cartilage. He cannot qualify for a cartilage transplant, but has tried gel injections. At most, they injections offer only temporary relief from chronic pain that he now and for the rest of his life will suffer from (although he attempts to hide it from everyone). Anyhow, my reality check is not to negative in such a way that discourages you from running (it as not as stressful on the knees as soccer anyhow), but get at least this message: I'm my dad, if he had the chance, would have chosen a non-ipact activity where he could go all out in and still managed a relatively pain-free retirement, if he had known the ultimate effects. Granted that you are young, that you don't play soccer, that you are in an entirely different context, it is still good to note this warning to stubborness. Theres a fine line between stubborness and determination, or maybe they're the same thing. Either way, check your values. What are you running for?