The ROM on flexion, extension, abduction, internal rotation, external rotation remarkably improved immediately after US-FHR on the CHL. The improvement after US-FHR on ROM was generally maintained throughout the consequent procedures. The total change at the end of the interventions was numerically higher than the change with the 1st US-FHR, which may support the idea that repeated US-FHR, or the combination of US-FHR and rehabilitation, may additionally improve shoulder ROM. Pain VAS at the maximal ER position showed an improving trend over time, which was not the case with VAS at rest. SPADI showed remarkable improvement between the 1st and 2nd visit. This result may indicate that US-FHR on CHL works for both pain on motion and disability of the patients with global limitation of shoulder ROM. We also observed recovery of CHL stretchability with US-FHR by dynamic ultrasound evaluation, which may explain why this technique facilitates improvements of shoulder ROM.
The mechanism of US-FHR is not fully understood yet. A previous study of US-FHR targeted the hyperechoic lesion in the multifidus muscle and assumed that the injected solution might affect pain receptors in the abnormal fascia visualized as a hyperechoic area 17. Another possible mechanism is that releasing (separating) “stacking” fascia in the CHL increased shear strain, leading to ROM recovery. Stacking fascia (also referred as “fibrosis” of the fascia) is usually visualized as thickened or high-echoic regions on Ultrasound 19, and a report showed these sonographic changes correlate with pain, a greater reduction in fascial shear strain, and also reduced lumber ROM in patients with low back pain20.
US-FHR differs from similar injection techniques in several ways: trigger point injection in myofascial pain syndrome usually does not use ultrasound and the needle tip does not target the fascia. The appropriate depth of injection for trigger point injection (TPI) is still under debate 21. Hydrodissection separates two anatomically adjacent components with a clear border, such as a peripheral nerve and its surrounding tissue, often using a larger amount of solution 22, whereas US-FHR injects as little as 2 mL of normal saline alone into the fascial tissue that looks thickened on ultrasound, intending to loosen and unglue it, without triggering a clear separation from the adjacent tissues. We assume that 2 mL is enough for this technique because a cadaveric study showed 1.0 mL of a pigment solution injected under ultrasound guidance separated two adjacent muscles (trapezius muscle and rhomboid muscle) and spread to the wide area within the interfascial space (24.5 cm2 on the deep side of the trapezius muscle and 18.8 cm2 on the superficial side of rhomboid muscle) 23. Hydrodilation is sometimes used to treat frozen shoulder; this involves the injection of large amounts (often as much as 30 ml) of normal saline and steroids inside the shoulder capsule, leading to rupture of the capsule 24. In contrast, US-FHR on the shoulder aims to release the fascial tissues outside the capsule, altering the sliding of the adjacent tissues. Prolotherapy triggers local inflammation by injecting dextrose, resulting in production of substances that promote tissue healing such as platelet-derived growth factors 25. Contrastingly, US-FHR does not seem to affect the inflammatory process or humoral factors as ROM and pain are altered immediately after the injection.
US-FHR has several advantages over the other injection techniques. First, the procedure takes a very short time (usually only 30 seconds), and the results appear immediately after the procedure. Second, it uses normal saline alone, which is cost-effective and safer than other drug solutions such as corticosteroid or local anesthesia. We also favor normal saline in US-FHR, as one study showed that normal saline was more effective than mepivacaine for TPI in myofascial pain syndrome 26. Third, ultrasound guidance enables clear visualization of the target tissue as well as the structures around, which makes the injection procedure safe. Moreover, comparing the sliding motion before and after the procedure by US informs us whether the injected target contributed to the functional impairment or not.
This study has several limitations. First, it was single-arm study and included only 11 patients due to relatively severe inclusion criteria. However, despite the small number of subjects, their ROM, pVAS at max. ER, and SPADI showed a statistically significant improving trend with US-FHR. Second, it is unclear if the effect of US-FHR lasts more than a week. Third, the response to the US-FHR varied widely among the subsects, and prediction models must be constructed to assess the efficacy.
Recently, the concept of “fascial system,” comprising the three-dimensional continuum of soft, collagen-containing, loose, and dense fibrous connective tissue that permeate the body and incorporate various type of connective tissues from adipose tissue to ligaments, has been proposed 27. In this novel point of view, both the CHL and adjacent peribursal fat are a part of the fascial system, therefore what we have called “capsulitis” (such as frozen shoulder, adhesive capsulitis, or periarthritis) is a problem of fascial system.
In conclusion, US-FHR on the CHL with or without rehabilitation might be an effective, less invasive, and inexpensive treatment for patients with global limitation of shoulder ROM. The safety and effectiveness of the procedure should be further evaluated with controlled trials with large number of patients and longer follow-up time. We would hope that our description of this novel treatment approach targeting the fascial system surrounding the shoulder sheds new light on the pathophysiology and treatment of this condition.