Hi clasch,
As the short description on the link you attached mentions, prolotherapy is an injection intended to cause an inflammatory response, classically used in ligamentous instability. In all of the sound evidence based research related to ES, by it’s definition, no where is ligamentous instability (stylomandibular ligament or otherwise) noted as an etiology. If anything giving that kind of injection would cause more inflammation in an already inflamed region with loads of nerves in the area. The injection would not have any affect on the length or angle of the styloid or the calcification of the stylohyoid ligament if that is present, nor would it address any potential vascular stenosis (notice none of these characteristic finders of ES were mentioned in the article or video)
Watching the video clip in the link it was shocking to hear this man (not sure what it takes to qualify as a “prolotherapy doctor”) say you could diagnos ES by pressing behind your jaw, if it is tender that is ES and this injection is the answer…massive red flag.
I didn’t have the eyeballs or energy to dive into the references listed or the rest of the website but just the surface information is scary - to me anyways. Hope my 2 cents are helpful, just my opinion. Good luck and proceed with caution.