Table 1 Patient eligibility criteria

   1. Pain upon abduction of the shoulder with painful arch;

   2. Shoulder pain as a recurrence of an episode with a maximum duration of 12 months in which a partial or good response is achieved with subacromial corticosteroid injection(s);

   3. A maximum duration of six months of shoulder problems prior to the first subacromial injection, possibly treated with non-steroidal anti-inflammatory drugs (NSAIDs) and/or physiotherapy;

   4. No shoulder problems for at least two years prior to the current episode of shoulder pain;

   5. Men and women, aged between 30 and 60 years;

   6. Being able to give an informed consent.

Exclusion criteria:

   1. Shoulder girdle pain;

   2. Shoulder pain not based on pain upon abduction of the shoulder;

   3. Signs of cervical root compression;

   4. Bilateral shoulder pain;

   5. Secondary subacromial impingement;

   6. Presence of specific rheumatic diseases;

   7. History of severe trauma of the shoulder within the previous two years (e.g. fracture, luxation);

   8. History and/or clinical symptoms of a large rotator cuff tear;

   9. Previous surgery of the affected shoulder;

   10. Extrinsic causes of shoulder pain;

   11. Presence of dementia or other psychiatric disorders;

   12. Not being able to fill in questionnaires in Dutch.