There is no single formula used by every ortho program. Some probably heavily consider AOA status and class rank while others look more at Step I score others look heavily at other things. You just need to apply to enough programs to make sure that you can get enough interviews to match. I've never seen any specific info from any program about exactly how they weight the pieces of our apps though there is that generalized JBJS paper out there talking about what parts of the app are important.

The JBJS article is - Orthopaedic Resident Selection Criteria
Volume 84-A Number 11 Nov 2002, Bernstein et al.

Hope that helps