Excellent question doc! :-)
First thing you should know is that hand measurement of x-ray has several inherent problems which are corrected by x-ray digitizing.
1. Foremost is the problem of covering up potential pathology. I know that it is a long shot, but none the less, a criticism which may have real-world overtones in a court of law. Many doctors use inappropriate size instruments, such as grease pencils, markers (often the indelible type :-( ) which might indeed cover a lesion, fracture or other pathology.Even digital analysis requires that you "landmark" the film with tiny dots, so you must take care to read [or have your films read] before you make any marks on the film to avoid this potential problem.
2. Even when time is taken to carefully measure distances, angles and curves, inter and intra-examiner reliability studies have consistently demonstrated a level of error that is unacceptable. In my own interpretation practice, I have seen such measurements where the number of millimeters representing a pathology (say 3.5mm) was actually 1.4mm on digitizing. Simply stated, hand measurement is prone to significant error as opposed to accuracy obtained from digitizing.
3. In order to measure enough different types of slippage, rotation ,etc, you would literally be spending too much time on the film, and it would begin to look like a road map. Digitizing allows you to tell the software which measurements you want and in what order and then you get a series of printouts that are not only quantitative, but easy for other clinicians, your patient or an attorney to understand.Dr. C