What's actually causing it
A tendon is the tough cord that joins a muscle to bone. Your gluteus medius and minimus sit on the side of your hip. Their tendons attach to the greater trochanter, the bony bump you can feel on the outside of your upper thigh 1.
This surprises most people: the tendons aren't normally inflamed, which is why rest and anti-inflammatory tablets often don't fix it 1. The nearby bursa, a small fluid-filled cushion, shows changes on scans in only a minority of people 3.
Load and compression are what aggravate it. Pain tends to flare with deep squats, stairs and impact exercise 1. Reducing compression on the tendons is one of the main principles of managing it 3. Patient guidance also lists everyday positions to avoid: crossing your legs, standing with your weight hanging on one hip, sitting in low chairs, and sleeping on the sore side 1.
It's recorded in about 1.8 of every 1,000 patients a year 6, and while it's most common in women over 40, younger people and men get it too 3.