I second the walking stick suggestions. I used them for the first time in Nepal and they made a HUGE difference, especially down hill. And up hill :-}

I returned from my 20 month RTW trip a few weeks ago, so I thought I'd update this thread.

Overall, my knees were fine, but I did have a very sharp pain in one knee early in the trip, a few days after spending 5.5 hours hiking the Tongariro Crossing in New Zealand. I think my pace was too quick, and unnecessarily so because I was trying to keep pace with another person.

The pain was so bad on one short walk a few days later that I practically keeled over and wondered if I'd need to be carried back to the hostel. It scared me, but I decided to be over-cautious, rest it, and try not to worry. Instead of a day-long glacier hike, I took a helicopter up Franz Joseph and limited the actual cramp-on hiking to 1.5 hours. I still had to be ginger, especially on ice, but that experience was a non-negotiable! After another week or two, I was fine.

In Nepal, I did a 10-day Annapurna Sanctuary Trek. I had some soreness, but who doesn't trekking in the mountains? My guide gave me massages with Tiger Balm, and I used a walking stick. My body adopted to the new stresses, as occurred with most of the trekkers. Me and my friend had also hired a porter, which kept the weight I carried to a minimum.

I never had a recurrence of the runner's knee pain which lead me to physical therapy, despite going several months in flip-flops vs my sneakers (w/orthotics).

I am so glad I didn't let fear/anxiety stop me from taking the trip, or doing the activities I wanted once I was traveling.