Other methods of treating open fractures
I might be able to help re: open fractures and closed treatment. Often an open fracture is initially treated with an external fixator to stabilize the fragments and closed reduction is performed (manipulation), with just a washout or debridement of the open wound site. You can code this with the appropriate external fixation code, for example, uniplane 20690, then the closed reduction code, for example 27825, and then code the fracture debridement, using a code that describes the deepest level tissue that was removed. Sometimes the fracture will heal with no open treatment after this, and eventually the fixator can be removed, and the wound treated until it heals. Or, the physician may plan to place internal fixation and you would use the ORIF code, with modifier 58, because this would be a staged procedure. If an IM nail is placed instead of a plate type of fixation, then you would use the appropriate closed treatment, IM nail fixation code. You can report debridement of the site of the open fracture separately with modifier 59, since the IM nail is inserted at a location on the body that is different than the open fracture wound.
Many closed fractures require open treatment, and many open fractures can be treated with manipulation or stabilization without needing any incision. CPT codes for open fracture treatment used to all be "Open reduction, internal fixation" but new techniques to surgically manage open fractures made the AMA change to "Open treatment" which will have in the descriptor, "with internal fixation, when performed".
Also, I might mention that open or closed fractures can be treated with percutaneous fixation. Percu fixation will tend to mention the use of fluoroscopy to guide pin placement into the fragments, and you usually see very small incisions just to admit the K-wire or screw or small plate. No debridement of an open fracture will be done. With open treatment, the op note will say the fracture was manipulated "under direct vision" and this may be either through the open fracture wound, or through an additional incision to approach the fracture site.
I am not able to explain why closed treatment with or without manipulation codes are paired with only closed fracture diagnosis codes in most coding books and software.