I found the broken down percentages of orthopedic surgeons off Wikipedia (don't know how accurate the numbers are), so if you can figure out the percentage of ortho's compared to all the physicians in the U.S. then you probably have a good estimate.
Of orthopedic surgeons applying for certification with the American Board of Orthopedic Surgery between 1999 to 2003 these were the percentages of surgeons in each specialty area:
- General orthopedics: 54.8%
- Spine surgery: 11.3%
- Sports medicine: 10.8%
- Hands and upper extremity: 8.7%
- Adult reconstructive: 3.9%
- Pediatric orthopedics: 3.4%
- Foot and ankle: 3.1%
- Trauma: 2.6%
- Musculoskeletal oncology: 1.3%
