There is no magic pill. Those injections were what allowed him to play and win slams despite his poor knees. If it weren't for those injections maybe his career or slam titles would've stopped in 2009 after he pulled out of wimbledon.
But there is a limit. Medical treatments can only do so much. nadal has definitley taken advantage of all the state of the art treatments there are out there.
That's certainly what one would expect at his level and likely the case he get's the best treatment available. But it can only do so much against a failing body.