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