I'm currently sacrificing a book to save my knees. In a previous post I wrote about how I lock my knees while I'm playing (a result of nerves and habit I think). Well, this, combined with hiking, wrestling with my son, and yoga, have resulted in my right knee being in a lot of pain. I was told that the pain was, in part, due to locking my knees as it puts greater pressure on the knee. Now that I'm in a bit of pain, I lock my knee all the more when playing and then have to hobble away in even greater pain.
A solution: In trying to break this habit, I've been carrying Three Nights in Havana Pierre Trudeau, Fidel Castro and the Cold War World by Robert Wright to gigs and rehearsals. I put the book under my right foot. This forces me not to lock my knee, but rather have a small bend in my knee. (The book is about 300 pages.) As a result I'm taking notice of my knee-locking habit and, so I'm told, keeping a small bend in my knee will strengthen the muscles around my knee.