The synovial membrane of the hip joint should be white. When the hip joint is irritated or painful, it becomes red and is often because the joint lining (Synovium) is irritated or inflamed.
During the hip arthroscopy procedure, we clean out the redness and get rid of the inflammation that has been causing the pain. Cortisone injections can sometimes get rid of the inflammation (just like Visine eye drops can get rid of the redness), but if there is damage inside the hip, the cortisone is usually ineffective or the pain just comes back after a short while.
Arthroscopic synovectomy, CPT 29823, is one of the few recognized codes covered by most insurance carriers. The key to treating this condition is to treat the underlying problem (labral tear, FAI, loose bodies, etc.), which causes the synovitis to be present in the first place. Once that underlying condition is successfully treated, the inflammation usually resolves and does not come back. The inflammation can be limited to the capsule/synovium or it can extend onto the labrum. In either case, a hip that is red and inflamed inside is a hip that hurts!
In almost all cases of hip arthroscopy, we encounter synovitis and we clean it out. If you've had hip arthroscopy elsewhere, take a good look at your pictures and see if you can understand where your synovitis was and how intense it was. That will likely give you useful information and insight into your condition.