Free Weights vs Machines

[TimM]

Everyone claims free weights are better, and I don't doubt that they do a better job in most cases. But my main concern is this:

"[F]ree weights require the help of a spotter, and result in more injuries than machines." LINK

Eventually I'd like to post about the machines I'm currently using and what I can do instead, but I will need to address the fact that a) I'm 40 years old, b) I have a prior knee injury which I am worried about re-injuring, and c) I won't have a spotter at the gym.