What Can Cause A Deep Indentation On Buttock?

Hello. I am 39 years old, 5.5 feet tall and weigh 145 pounds. I have a very deep indentation in my left buttock/hip. I have been fighting back pain with radiating pain down my leg/foot for the past 2 years. I have had multiple surgeries for herniated disc at L5/S1 with nerve root compression, to no avail. On my most recent films, the nerve root is displaced to the rear, I have bulging disc at L4, L5, mild central canal stenosis at multiple levels, moderate central canal and left neuroforaminal stenosis at L5/S1 level. Trace retrolisthesis at L3/L4, mild scoliosis to the left, exaggerated curvature. What is causing the deep indentation? What is the next step in treatment for me?