While I agree with most of what has been said in this review, the statement above is in error. In the novel Patriot Games (which I am currently rereading following the author's untimely death) Ryan's history is explained in some detail. This includes a brief time in the Marines that is ended when, as a newly commissioned lieutenant, the helicopter he is in crashes resulting in a major back injury. Ryan the works on Wall Street where he meets Cathy Muller who is studying to be an ophthalmologist and knows a surgeon who repairs Ryan's back. It is after this that he turns his back on Wall Street and starts teaching history at Annapolis before being recruited by the CIA.

This was not something thought up by the director, and while not being covered in "real-time" in any of the books, it is definitely part of the canon and a major part of the backstory of the character that is referred to multiple times throughout the rest of the series.