Hi Sandy,
Personally I don’t see much impingement of subscapularis.
To assess for subscap impingement you need to use internal and external rotation and look for impingement under the coracoid process.
There is usually plenty of space for the tendon to pass through , hence impingement is fairly uncommon.
I have seen impingement associated with gross tendinosis of subscap or even with large hydroxyapatite depositions in the subscap tendon. In both of these examples the subscap tendon is much larger than usual and hence the impingement.
I also like the internal and external rotation dynamic assessment to assess that the subscap tendon is actually attached to the humerus and moves in step with the humerus. If it is ruptured the humerus will rotate between the stationary and retracted tendon and no collagen will slide with the bone.
There is a clinical test for subscap rupture called the “lift off test”
Place the back of your hand against the small of your back and try to move your hand away from your back. If you have an intact subscap you can do it, if you have a ruptured subscap you can not.
Steve.