I also wanted to see if there was a controlled study comparing running on pavement to running on soil or sand, in terms of osteoarthritis or acute injuries. In this I admit I was partly motivated by my snooty trail-runner's disdain for the very roadist culture of the San Diego running community.
Surprisingly at least to me, no such study has been done. Common sense (and expert opinion, i.e. orthopedic surgeons) say soil is better. Unfortunately in medicine, the weight of expert opinion isn't as good as good old data, and it's labelled as mere Class C evidence; in contrast, the Australian meta-analysis above is by definition Class A, because it draws from multiple controlled studies. That said, the Australian study is somewhat limited because it looks at anatomy correlates of knee damage, rather than at the clinical manifestations of osteoarthritis (as in the Stanford study), which is what we care about. That is to say, sure there are osteophytes, but how much more or less often do runners' knees hurt than non-runners'? This looks like a sports medicine study waiting to happen! (Incidentally, here's another post with some more information but which still found the same lack of data on this question.)
I had been coached in high school track that running frequently on sand was bad for your knees, and I'd long stuck with this belief. But I recently revisited that belief based on a conversation with a long-time distance runner patient of 70 years who prefers running on the beach, and whose knees are none the worse for it. There's no study there either, so again for now we'll have to provisionally go with common sense/weight of opinion, and I've now updated my belief that sand is bad for your knees, to sand is probably at worst neutral and maybe better than pavement.
1. Long Distance Running and Knee Osteoarthritis: A Prospective Study. Eliza F. Chakravarty, MD, MS, Helen B. Hubert, PhD, Vijaya B. Lingala, PhD, Ernesto Zatarain, MD, and James F. Fries, MD. American Journal of Preventive Medicine. 2008 August; 35(2): 133–138.
2. What is the effect of physical activity on the knee joint? A systematic review. Urquhart DM, Tobing JF, Hanna FS, Berry P, Wluka AE, Ding C, Cicuttini FM. Medicine and Science in Sports and Exercise. 2011 Mar;43(3):432-42.