See video below for 3 clinical tools to screen for true frozen shoulder.
To sum up:
1. Pain at end range ER passively by side. No active motion here, only passive.
2. #1 can lead us to many disorders so I like to further narrow it down. 30 degrees of ER by side passively is my cutoff. Anything more usually is not frozen shoulder (give yourself a little wiggle room though).
3. No pain to provocation to anterior or lateral subacromial space. If this creates pain, more than likely rotator cuff.
Now there is usually a derangement of the shoulder that will put undue stress on the RTC and have pain arising from this dysfunction too. However, I do find these 3 clinical tools give me bang for my buck for true frozen shoulder.
Of course you need to consider the whole picture and not just these clinical tools but this is usually what I see (age, comorbidities, MOI, etc.) What do you think?