In reply to Chris the Tall:
ohhhh yes.
after lots of physio investigation, resulting in orthotics, I got fiendishly bad patella tendonitis, particularly in my right leg.
the patella strap was the main thing that sorted me out, together with exercise.
most knee supports are bollocks (particularly those neoprene ones - neither use nor ornament) but the patella strap made a significant difference to me. Mine had a 'lumpy bit' which pressed into the patella tendon, then it closed with a velcro closure at the back.
I recommend! I use mine in the gym, but don't use it when out on the hill as it gets in the way when stepping up (for instance when scrambling).