"Tendinitis of the Shoulder" is pretty vague to start with. The question/query needs to be more specific. In general, when a physician, particularly an Orthopedic Surgeon, speaks of "Tendinitis of the Shoulder," he/she is usually meaning "Rotator Cuff Tendinitis," which does not even have a specific code in ICD-10. In general, ICD-10 has made a real mess of this whole concept of Tendinitis, Bursitis, Synovitis, and/or Tenosynovitis of the Shoulder (but not it alone). It is far too complicated, fragmented, and confusing for anybody to figure out. I note that none of the previous responders to this has even mentioned the M75. Code Set for "Shoulder Lesions." Unfortunately, it/M75 does not include "Rotator Cuff Tendinitis" in its list of shoulder disorders, even if it is probably the most frequent diagnosis made to explain shoulder pain. In one of my Blogs (Shoulder Pain and ICD-10) at icd10orthocoder.com, I have "tried" to sort this out as best I can, but even then there is room for confusion &/or debate. I would suggest reading it.
Respectfully submitted, Alan Pechacek, M.D.
icd10orthocoder.com