Here is a question and answer from an avid runner who is a member of the Veterans running Club of Hong Kong. It is an interesting case study:
I noticed that when do the weighted leg raises in the lying position (the 3 different angles of the leg exercise), when I do the backward angled leg - very noticeably on the left side I am not getting any glute activation. When I do this leg raise all the work is being done by the hip//lowerback/QL area muscles! On the right side it is less pronounced, but still might be a similar thing going on. In fact its only really in the centre position that I really feel the glutes kicking in and getting tired.
Is this right? I assume not.
If I do it from a standing position (less gravity of course) it feels like the glute is working and the lower back is more relaxed.
Do you have any advice?
Great observation as the hip abduction with slight hip extensuion should be addressing the lateral Gluteus Maximus and the Gluteus medius.
If you are recruiting muscles in the lower back it explains the theory that when a primary muscle is not firing the secondary synergist muscles take over.
You can see clearly from the MRI that you have had effusions on the insertions of both Gluteus Medius and Minimus whiuch indicate an overload on those tendons. It seems like they have shut down and will need to be carefully nurtured back to a functional state. I would work on straight leg hip extensions with resistance and bent leg hip extensions to reactivate the gluteals and the hamstrings.. Carry on with the simple squats with foot turned out and foot straight as this really engages the Gluteals. If you want to add some dynamic action add a small jump to the squat. This really kicks in all the Gluteals.