Putting together my 38 years of nursing experience and common sense, I suggest that avoiding repetitive strain injuries means avoiding the *repetitive* strain. I believe that an occupational therapist or physical therapist who is willing to watch how you position your hands and arms to play your guitar might be able to suggest alternate ways to hold the instrument or position your hands and arms to decrease the strain. You may need to shift your hand/arm positions around, that is, not use exactly the same positions for the same chords all the time, use different guitars, learn to relax muscles and joints when you're not actively using them, and do your playing in short sessions with stretching and relaxing exercises in between. Best of luck.