Participants will be randomised on a 1:1:1:1 basis to one of four treatment groups : ( 1 ) ultrasound-guided subacromial corticosteroid injection and a physiotherapist-led exercise programme , ( 2 ) ultrasound-guided subacromial corticosteroid injection and an advice and exercise leaflet , ( 3 ) blind subacromial corticosteroid injection and a physiotherapist-led exercise programme , or ( 4 ) blind subacromial corticosteroid injection and an advice and exercise leaflet .