If either the pelvis or femur moves, we have movement of the hip joint. For this reason, when discussing hip openers, we must evaluate all potential movers & stabilizers of the hip & pelvis. This includes the adductors, abductors, flexors, extenders & internal & external rotators.
Our hips are the largest joints in our bodies. For that reason, our hips very often carry a great deal of mental & emotional trauma & unresolved pain. Too frequently, we avoid confronting these sensations & as a result, dump the weight into our surrounding joints. It is crucial that we be aware of any compensatory patterns in our practice & do our best to isolate the movement at the joint we are targeting. This becomes especially true in our hip-opening poses as often times, the joint that is being compensated is the knee. If we practice performance-based yoga, we try & match the external picture of the pose, instead of using our sensory awareness to locate & isolate the stretch at the intended location. This is a dangerous mindset & one that can leave us with torn tissues & damaged joints if we are not careful.
The knees (& shoulders) can be especially vulnerable joints. Respecting their capabilities with regards to our experience level & our bodies readiness for different poses can mean the difference between a fulfilling, lifelong practice, & that one time in class that you did lotus or pressed up into a handstand. Not that we should avoid those poses, but should approach with respect & only when our bodies are ready to receive them.