I am coding an inpatient consult for infectious disease MD. The pt has a nonunion of a subtrachanteric fracture (RT femur) following an ORIF done 6 months prior to the consult. Infectious disease process was ruled out. There is no documentation in the entire inpt chart to determine if the fracture was traumatic or related to osteoporosis nor is there documentation to support an external cause code. The code M96.89 (other intraoperative and postsurgical complications and disorders of the musculoskeletal system) has been suggested. I think S72.21XK (diplaced subtrochanteric fx rt femur, nonunion) is the most accurate code however I cannot provide an ext cause code associated with the fx. Though I can’t find a specific statement, the guidelines for Chp 19 seem to indicate an ext cause code should be associated with codes from that chapter. Is it necessary to provide an external cause code for every Chapter 19 code? How would you code this?