Found this interesting. It's from 2004, but I don't think anything has essentially changed in the meantime that would make the results invalid for the present time.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1725005/pdf/v039p00029.pdf
QUOTE:
CONCLUSIONS
(1) There is a threefold greater risk of injury in tae kwon do
than in Shotokan karate.
(2) Injury rates and types of injury in Shotokan karate and
kung fu are similar.
(3) Different martial arts have different distributions of
injury by body region.
(4) There are no significant differences in injuries between
sexes.
(5) Martial artists under 18 years of age are at significantly
lower risk of injury than older athletes.
(6) Athletes >18 years with at least three years of experience
are at greatest risk of sustaining major injuries (35%) and
multiple injuries (35%).
(7) Athletes ,18 years old with ,3 years of experience have
a low risk of multiple injuries (5%) and an extremely low
risk of major injuries (,1%).
END QUOTE
I thought it was interesting that the study concluded that older-than-18 martial artists with 3 or more years of experience were at significantly greater chance of injury than younger and inexperienced students.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1725005/pdf/v039p00029.pdf
QUOTE:
CONCLUSIONS
(1) There is a threefold greater risk of injury in tae kwon do
than in Shotokan karate.
(2) Injury rates and types of injury in Shotokan karate and
kung fu are similar.
(3) Different martial arts have different distributions of
injury by body region.
(4) There are no significant differences in injuries between
sexes.
(5) Martial artists under 18 years of age are at significantly
lower risk of injury than older athletes.
(6) Athletes >18 years with at least three years of experience
are at greatest risk of sustaining major injuries (35%) and
multiple injuries (35%).
(7) Athletes ,18 years old with ,3 years of experience have
a low risk of multiple injuries (5%) and an extremely low
risk of major injuries (,1%).
END QUOTE
I thought it was interesting that the study concluded that older-than-18 martial artists with 3 or more years of experience were at significantly greater chance of injury than younger and inexperienced students.