Because of the big soft tissue space above the knee - the suprapatellar space - it is not uncommon for a knee graze to end up with infection within the knee.
A graze is a superficial injury where the knee is scraped along a rough surface, eg the road.
Because of the big soft tissue space above the knee - the suprapatellar space - it is not uncommon for a knee graze to end up with infection within the knee.