I find this highly fascinating because my acupuncturist and myofascial therapist told me a similar thing when I went in for treatment. She said that part of my problem was built up connective tissue in the back of my jaw. She felt around my face and the inside of my mouth (I know, weird) and said I had an overwhelming amount of it.
So I basically went under several months of myofascial release therapy where she released the connective tissue from the inside of my mouth by using pressure. The connective tissue started in the middle of my cheek and went back deep into my jaw and even as far back as the corner of my lower jaw. Equally important is we worked a lot on releasing tissue and tension around my whole upper body, and predominantly around my neck.
Many other forms of therapy such as rolfing and feldenkrais use similar methods of helping the body release tension. It was very very very painful releasing the tissue. But! It was definitely needed and it actually changed the way my face looked and felt (my right side of my lip and face looks more equal to my left now without the upper lip pulling back and upwards on that side, which gave me a weird appearance). I wish I had known about it before, even as a non-injured musician in the past! A professional European horn player told me that he also received this, even if he isn't injured because it's important to take care of the body. Warming-up is always not enough.
We have to treat our bodies like athletes, even if it's use of smaller muscles. A lot more goes into playing than we give credit because we are not aware, and tension can build up over the years....and not necessarily because we're doing anything wrong, but because it is natural. Some people can take a beating for years and years and not feel anything, whereas others are more prone to overuse because of their physical makeup, or even genetics in the case of onset of dystonia.
We just have to take extra measures that are not traditional to keep check on tension....which is hard to do since most often injuries sneak up on us and slowly degenerate our ability over time before we are even aware of it.
Also a lot more muscles come into play than we know. Most brass musicians consider their embouchure as only the use of the muscles around the lips, and never understand the actual anatomy or function of the muscles in the face (where the muscles connect to, what each on initiates) and that the neck and upper back muscles make a great impact on your playing too, since they tie into the facial muscles and nerves around the jaw.
Additional notes: Thank you to Scott King, DC for getting in touch with me! If any injured musicians are in the Denver/Colorado area and looking for soft tissue diagnosis and treatment, Scott is available and has trained with Dr. Brady who wrote the article I shared above. I offered to share his contact information below:
Scott King, DC
Novo Soft Tissue & Spine