You might consider more sophisticated conditional value lists than the basic design and there are also alternative methods for selecting from a dynamic list of values that you might consider. See the links that I've added at the end of this comment if you are interested in pursuing those options.
But another option that I've used with the Tutorial section of the Known Bugs List database also comes to mind. Each tutorial record is a "tip" for using FileMaker more effectively that I might use in creating a post here in the forum. I need to be able to find these very quickly. So I added a text field to the table where I enter a return separated list of key words. To apply it to your project, each of the different methods for naming Total Hip Replacement would be a different row of text in this key word field on your THR record in a table of such procedures.
I then set up a global text field with an auto-complete enabled drop down list of the key words from this text field. Each row of text in that field will be a different value in the value list. By typing just a few letters, the value list filters down to just a few possible options. When I select an actual value from this now narrowed list, a script uses the text thus entered into the global text field to perform a find to bring up that record. In your case, that script could return the ID of the procedure record thus found to enter into a corresponding ID field of the record you have just created to record a patient's treatment.
You might check out the Adventures in FileMaking series. Adventures 1 and 2. They are free to download.
Adventures in FileMaking #1 - Conditional Value Lists (includes details on how to set up a basic field based value list)
Adventures in FileMaking #2 - Enhanced Value Selection (what to do when a simple value list won't cut it.)