Have you noticed? When you go into an American Dojo you can hear the mechanical clicks of the knee braces throughout the class. Yet when I lived in Okinawa I never saw an Okinawan Shorin-Ryu practitioner with a knee brace on (unles they injured it outside of the dojo). Why?
The reason is both clear and disturbing. The infamous roundhouse kick: the mawashi-geri.
Okay here's the even bigger news: mawashi-geri is NOT a Mataubayshi-Ryu technique! Don't believe me? Look it up. Still most every Matsubayashi-Ryu dojo uses the roundhouse kick - and many of those dojo members have bad knees.
There is a reason Nagamine Hanshi did not include it in basis techniques when he developed Matsubayashi-Ryu: it's ineffective. Sure you can occasionally score a point in competition but Matsubayashi-Ryu is not about competition, its about fighting in the street. In a real fight, a kick targeted above the waist is an invitation to test your ground skills.
I know what you're going to say "But kickboxers use roundhouses all the time as do the Korean Arts." and you are absolutely correct. However remember Korean arts (regardless of what they say) came from Shotokan (Japanese) which came from the Okinawan arts. You never see a 60 year old Korean throwing roundhouse kicks but even Nagamine Hanshi could throw conventional kicks in his 80s.
I understand a beautifully executed mawashi-geri impresses your friends and influences judges, but its sort of like smoking; by the time the damage begins to show (i.e. your knees) its too late.
Again it boils down to a simple question: are you studying traditional Okinawan karate or a bastardized American version of the art. Art vs. sport.