The US Pony Club has some stats on their kids while riding English:
http://ponyclub.org/pdfs/spring20042.pdf
Here is another study:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Retrieve&list_uids=11958244&Dopt=Citation
Injury during contact with horses: recent experience with 75 patients at a level I trauma center.
• Griffen M,
• Boulanger BR,
• Kearney PA,
• Tsuei B,
• Ochoa J.
Department of Surgery, University of Kentucky, Lexington, USA.
BACKGROUND: The objective of this study was to examine equine-related trauma at a trauma center servicing a region in which there is significant contact between horses and humans.
METHODS: Data were collected on all patients admitted to the University of Kentucky Medical Center from January 1994 to December 1998 for treatment of horse-related injuries.
RESULTS: Seventy-five patients were admitted to our center after injuries due to contact with horses (0.75% of all trauma admissions). There were 42 men (55%). The mean age was 37 years (range, 3 to 81 years). The majority of patients (67/75) were injured during recreational activities, and most fell or were thrown (40/75). Only 14% of patients were wearing helmets.
The most common injuries were extremity fractures and head injuries, but thoracic and abdominal injuries were not rare. Of the 75 patients, 34 required surgery. Five patients (6.7%) died, all of head injury. During the study period, 11 people died in Kentucky due to contact with horses.
CONCLUSIONS: Injury due to contact with horses is uncommon even at a center servicing a region with a large equine population. However, injuries are often serious and lead to significant morbidity and occasional mortality. Prevention of death from horse-related trauma is synonymous with prevention of head injury.
That's the key. WEAR YOUR HELMET - even when you're not jumping. You may get some orthopedic injuries (I have several) but you can get those in almost any sport. Head injuries are the real danger in riding.
I have always worn a helmet, my dad was a bug about it when I was a kid. They didn't have the real safety helmets in those days, so he sent off to New York for a jockey's racing helmet. UGLY - I got a racing silk cover for it.