The Effect of Arthroscopic Subacromial Decompression in Patients Who Are Non-responders to Non-operative Treatment.

Inclusion Criteria: * SIS diagnosis (Consultant's clinical diagnosis of SIS + at least 3 out of 5 positive tests from the following: Hawkin's, Neer's, Jobe's, Painful arc and external rotation resistance test) * Positive subacromial injection test * Insidious onset of shoulder pain * Considered a surgical candidate by an orthopedic shoulder specialist. * Symptoms for at least 6 months * Completion of at least 3 months supervised shoulder training * No improvement in symptoms for at least 3 months * The patient must be expected to be able to attend rehabilitation and post-examinations. Exclusion Criteria: * Terminal illness or severe medical illness (ASA score higher than or equal to 4), systemic musculoskeletal disease, inflammatory joint disease (e.g. rheumatoid arthritis), symptomatic cervical spine pathology or thoracic outlet syndrome. * Full-thickness rotator cuff tear, calcified tendonitis, labral tear, frozen shoulder, biceps tendon pathology, acromioclavicular osteoarthrosis, glenohumeral osteoarthrosis or other concomitant shoulder pathology. * Previous surgery or radiotherapy on the affected shoulder. * Pregnancy * Ongoing workers compensation case or job rehabilitation process