The hip is a ball-and-socket joint, where it is the largest weight bearing joint in the body. The joint allows for several types of movement in the body: Flexion, extension, abduction, adduction, external rotation, internal rotation and circumduction. Healthy hips should allow such movements easily, but there are some limitations to our movements due to bone compressions (bones bumping one another), ligamentous (near its end range, ligaments become taut), muscular (muscles generate passive tension near end range) and soft tissue compression (E.g. the abdomen pressing on your thighs during a forward bend). However, there are some anatomical issues that may affect your hip mobility such as the shape/angle of your femurs as well as limitations by your soft tissues.
Warrior II or Virabhadrasana II is a lunging standing pose. Vira means warrior, Bhada means friend and Asana means pose – it helps the mind and body create awareness as it builds strength and power. This pose does seem anatomically difficult as the front hip is externally rotated on bent knees while the back hip is internally rotated while straightened. This pose requires a good flexibility and mobility of the hips.
As a relatively new instructor, cueing this pose by squaring the hips is an easy way to get beginners to understand where the hips should face. However, for some of us when we square the hips, the pressure is transferred from the back leg to the front hip/knee due to constraints mentioned above. The front thigh would move inwardly, pulling the knee in which could result in knee/hip pain in the long run. It might be better to keep the front knee on top of the ankle and let that thigh dictate the position of the pelvis – if it is not squared, it is acceptable. Some cues might work for individuals who are more flexible, but as practitioners, we should find what position works for our individual body to be able to feel stable and strong.