Should I use a lower gear?

Hi
I've had a THR (Right) in Oct 2009 and am due to have a left THR and TKR whenever I agree to go on the waiting list.

All three joints have OA but the knee also has a lovely step following a climbing accident.

So far I've said I'm not ready for surgery and I'm doing okay. Since I started exercising more (mainly cycling but some pilates) I've stopped tramadol and mainly use heat to relieve pain with some anti-inflammatories.

However recently my knee has become more swollen and painful. This seems to have happened about the time I started using higher gears on the bike and am wondering if the increased workload is the cause.

Question is should I continue using the higher gears (mid-range on an 18 gear bike) or drop back to the low ones 1 - 6?

Or is it just coincedence and my knee just have one of its periodic moans

Thanks for any advice
Pamela