The 30-year-old injured his back in March 2010, returning to action a year later.
Onions told Sky Sports News: "I've played nine Tests and from 2009, when it looked potentially as if I might not play any more, I wanted to play one more Test and would have walked away a happy man.
"But when you get fit and strong again, you want to play as much as you can.
"Of course, I'd love to finish my career playing 50 to 60 Tests, but that might not happen. You've just got to be proud of what you've done so far and keep working hard to try to force your way into the side."