The one time I did NOT wear my Thor knee braces (in my smaller race boot) I hit the deck hard and the Jawa's steel fuel tank smashed my knee into the ground side on. It crushed the meniscus somewhat.
Would have been at very least cushioned well by these guards, they have had big hits and crashes before and no probs with knee damage - till now.
Favouring my sore knee caused damage to the 'good' knee so both a bit poor in the joint now although, time, resting, and condroitin and creams seems to be helping.