I have been doing ultrasound "trigger points" for about 3 years now, and have this to add to what I've previously posted in other threads:
Sometimes a trigger point isn't what you think it is. For the purposes of this discussion, I will define a TP as any area of radiating or localized point tenderness to palpation, whether you can feel a lump or not.
Occasionally you will see a calcified ball of muscle on ultrasound, and these usually respond to repeated needling attempts the way we were all trained. The benefit of using ultrasound is that you do the needling in a directed fashion. In 3 years I have only seen a handful of cases like this, but they all responded well.
More commonly, you will see nothing out of the ordinary on your ultrasound exam. No calcifications, masses, tears, etc.
Trigger points often occur over bony prominences or ridges. These cases may represent bursitis, ligamentous or tendinous pain (most frequent, IMHO), peripheral nerve entrapment, muscular irritation (??), or any of the above combined with centralized hypersensitivity (take your pick of etiologies).
In "bony prominence" pain problems, I will attempt to inject such as to lift the localized tissues away from the bone, and hydrodissect any localized tissue planes theorizing that this may enter a bursa, break down soft tissue adhesions, or treat an inflamed tendon sheath. One obvious example would be the common GTB injection. Performed under US I can not only inject the space between the GM muscle/tendon and the bone (the "bursa), but I can also inject the more superficial tendon sheath, watching the soft tissue planes open up as I do it. These are usually far more effective than the many blind injections these patients previously had before seeing me. They are less effective in the obese, inactive types with a million other pain complaints.
Another fairly obvious example would be the supraspinatous tendon sheath injection. If you're not doing these, you are missing a glaringly effective treatment option for shoulder pain. Patients with point tenderness over the SST insertion on the humerus (have them put their hand on the hip to roll the head of the humerus forward, then palpate the superoanterior aspect), pain with resisted abduction, and attempted "reach around the back" are excellent candidates. If there are tears apparent on the MRI, even more so. With ultrasound you can precisely guide the needle between the deltoid and SST and watch the injectate flow over the tendon and wrap around the back toward the SS muscle belly. Patients get immediate relief and can now raise their arm easily- very satisfying. I do these on my wife periodically and she uses terms like "friggin miracle" to describe how well it works. Of course, most durable results are achieved when you combine the technique with appropriate PT, exercise, and shoulder care.
I have often found trigger points in the chest wall to be localized to the junction of the abdominal wall musculature where it rides up over the ribs, particularly at the costal margin. Abdominal wall pain is frequently localized to the junction of the oblique muscles and rectus sheath. Inject carefully at these precise locations and you often see surprisingly good results.
I have been remarkably successful treating seemingly random foot pain in this manner. One recent patient was complaining of plantar fasciitis, but also pain along the anterolateral aspect of the mid foot. One injection along the soft tissue planes (likely placed over the various tendon sheaths) actually resolved this as of a 1-month follow up. The plantar fasciitis did not respond as well. I treated another patient a few days ago with pain just inferior to the medial malleolus, anterior aspect. I injected at this exact location and saw three tendon sheaths flood open. Instant relief. Now let's see if it sticks.
One unusual case I had recently involved a man who sustained a minor trauma to the extensor retinaculum along his ankle, and had two years of very painful foot ischemia with walking/running. He was referred from vascular who couldn't help him, although there were some minor seeming flow abnormalities in the ATA. They thought he might have CRPS. The patient had selfie pics demonstrating the ischemia. His entire food would go white below the retinaculum. After a single injection directed at expanding the tissues under the retinaculum, he was markedly improved. He could now walk 3 miles before his foot would start to get ischemic, and the pain would now stop when he ceased walking. Previously it took 30 minutes to resolve and was extremely painful. He continued to improve with two more injection sessions.
Sometimes you will find patients to have a painful lymph node or lipoma, but if you carefully dissect around it with anesthetic, the goal being mobilization, they will improve.
The two most common "TP" areas I see include the bilateral cervical trap points at the base of the neck about 4 fingers off the midline. I believe these are well described. Also, the tissues just overlying the PSIS. I have had varying degrees of success injecting these with my techniques ranging from complete durable relief to none at all. Getting immediate improvement with the anesthetic is common, but durable relief occurs maybe 40-50% of the time.
I hope this helps to explain why those of us who use ultrasound are so adamant about it's benefits. In my opinion any pain doc who isn't learning to do these procedures is a dinosaur.