From what I've read, there is a 2 in 3 chance of arthritis being the cause if you suffer less than 23 degree internal rotation.
When I saw my physio (for first time) a couple of weeks ago, she put me on the table and did the test and immediately said there is no rotation and I probably have arthritis.
Then I saw an orthopedist and he did the same tests and said 15 degrees in the right, 45 in the left, and referred me for an MRI scan with his initial diagnosis coxarthritis and tendanitis of the femur biceps ( been having pain in the inside hip and groin too).
Haven't had the scan yet. Trying to do various stretches at home. Hoping it's just a bit of tendanitis caused overtraining and by me being always stiff and sitting at a desk on a hard chair 8 hours a day since the lockdowns.
I'm 49 btw.
I'm surprised there isn't more discussion on hip problems here. I started a thread on this last week and nobody replied. When I searched 'internal hip rotation' here there is hardly anything, yet apparently it's fundamental to stride length.