First, it's not clear your chiropractor could diagnose shoulder impingement (damage caused by injury and swelling to rotator cuff muscles) just by an x-ray. Physicians who diagnose this condition typically prescribe avoidance of repetitive activity that causes pain, stretching exercises/physical therapy and an anti-inflammatory drug (not all will help a given patient).

Willow bark contains salicin, similar to what's found in aspirin and can cause similar side effects (i.e. stomach distress and allergic reactions, as well as severe kidney problems in some people.

I'd look for a proper diagnosis before taking any more drugs, herbal or otherwise.

Here is a link that might be useful: Shoulder impingement syndrome