Shoulder AC, commonly known as frozen shoulder, is a self-limiting condition that affects three to five percent of the population and up to 20 to 30 percent in persons with diabetes mellitus. Its aetiology is still being understood with evidence supporting a chronic state of low-grade inflammation and elevation of pro-inflammatory lipoproteins resulting in fibrotic changes in the glenohumeral capsule. This results in pain, reduced shoulder range of movement (ROM) and functional disability that can spontaneously resolve between one to three years, with 40 percent reporting persistent symptoms at long-term follow up (mean follow up time 4.4 years, range 2 - 20 years). AC can occur spontaneously, as a primary insidious onset, or secondary, following a post-traumatic event such as shoulder surgery or rotator cuff injury. Treatment for AC commonly consists of conservative management interventions including pharmacotherapy, physiotherapy, and corticosteroid injection, with referral to secondary care if symptoms persist for interventions such as manipulation under anaesthesia and arthroscopic capsular release.
The treatment interventions or surgical procedures for AC may not always be effective or suitable for all patients due to conditions that may increase risk of complications such as respiratory conditions, allergies, previous surgery complications, co-morbidities (e.g., liver, cardiovascular and kidney disease), and patient choice. Untreated conditions and long-wait times can lead to chronicity further impacting an individual's health and increasing costs to the National Health Service (NHS). Musculoskeletal (MSK) conditions are estimated to cost to the British government an estimated £7 billion per year, accounting for one third of the NHS budget. In a United Kingdom (UK) health survey evaluating the prevalence of chronic pain (duration of pain 12 weeks or more), labelled MSK conditions as a long-lasting illness, accounting for 81 percent of participants, and of this, 24 percent involving the shoulder. Chronic MSK pain has also been linked to 17.5 percent of work absences, anxiety, depression, and health inequalities.
Over the last 20 years, EWST, has gained popularity as a treatment modality for orthopaedics conditions such as chronic tendinopathies. EWST can be generated as focused high- energy (\>0.60 millijoules (mj)/mm2) shock waves or emitted as radial low (\<0.08 mJ/mm2) to medium-energy (\<0.28 mJ/mm2) shock waves. ESWT stimulates soft tissue healing via a biological response of mechanotransduction through neovascularisation, reduction of tendon matrix inflammatory markers such as metalloproteinases and interleukins, assists with the migration and differentiation of mesenchymal stem cells, and enhances the natural healing microenvironment. To date, therapeutic EWST has been shown to be clinically effective to treat bone non-unions, chronic soft tissue disorders such as tendinopathies and recalcitrant MSK conditions commonly involving the supraspinatus muscle tendon, patellar tendon, Achilles tendon and plantar fascia, and has become a favourable alternative treatment for individuals who have exhausted conventional conservative interventions.
A review of the literature exploring the use of ESWT as a treatment for chronic AC found seven randomised control trials (RCT) reporting significant improvements in function, pain and shoulder ROM in groups that received ESWT. The literature found improvements in all outcomes within 12 weeks when compared to a control group.
Although the literature demonstrates positive outcomes, due to the small number of studies, small sample sizes, and heterogeneity of treatment protocols, there is insufficient evidence for it to be a recommended treatment for AC by national health guidelines (e.g., National Institute for Health and Care Excellence). Further research is therefore required to determine the acceptability and viability of this intervention in the UK healthcare framework, with potential to conduct a full-scale RCT.
