Hi Xue,
Take a look at the “joints” webinar as this will help with this question.
The supraspinatus can get enthesopathic changes as a result of chronic traction injury and this indeed commonly can lead to enthesis based partial then full thickness tears.
Seronegative patients can also get enthesopathic based disease which may similarly result in partial and then full thickness tears.
So there is some overlap for sure.
The times I suggest it is from seronegative origin is when the following things come into my consideration.
Enthesis disease in someone who has a desk job and is not active enough to have traction injury.
Patients with clinical skin psoriasis
Patients with multi locational disease
This may be multiple enthesis involvement in the same shoulder (eg supra and subscap) or multi seperate joints with enthesopathy
Patients with prior scaro-iliac joint inflammation previously
Patients with haematology evidence of seronegative disease
Patients with nail pitting, sausage finger, conjunctivitis etc
So I am looking for a pattern rather than features at a single tendon.
The clinical history, occupation and recreational activity is a good context for how much traction change you can expect.
Steve