Why is “Wild Thing” so popular? Is it because it looks cool, but is more accessible for many people than handstand or arm balances? There has been a lot of debate around this posture, primarily focusing on the very real risk to the shoulder joint. I don’t do it because it’s a twist within a backbend, which is a movement with an increased risk of vertebral subluxation (in this case, displacement of a vertebra anteriorly). And, in "Wild Thing," this increased risk is not rewarded with any benefit you can't get from much more anatomically sound postures.
In backbends, the spinal vertebrae should move anteriorly (forward) as the front of the spine opens into the posture. The action of the backbend (especially when not done with a proper understanding of how to traction the spine in the posture) will tend to go into the part of the spine that is already open, and the vertebrae in that area will receive more anterior pressure. (Check out the photo above and you can see that the majority of the backbend is in a few vertebrae; most every picture of backbends you see verifies this tendency, which calls for refinement of backbending technique.)
Add the rotational action of the twist, which will also go into the spine's open area, and you end up with a very few discs potentially getting a huge amount of anterior pressure. Unlike the sides and back of the spine, there are no muscular attachments to the front to help prevent a vertebra from slipping forward. For me, this is an unacceptable risk of potential injury, the results of which might not show up for years. So, I just don't teach it or do it.
I always think of shelling peas when I watch this posture (from the downward facing dog I stay in): open the front of the hull, bend it backwards to expose the pea, and then give it a good twist to pop the peas out.
Do a twist. Then do a back bend. Don't combine them. Your spine will love you for it.
2. Uttitha Hasta Padangusthasana B (a.ka. "The Psoas Wrecker")
In this pose, you’re essentially cantilevering the weight of the entire front leg from the lower back. That’s a lot of stress on an area where most people are already prone to pain. And what’s holding that leg up? Your hip flexors. Westerners are chronically tight in the hip flexors from being seated. Really, no one needs shorter, tighter hip flexors.
And, again, what’s the point of the pose? Some people profess to use it for abdominal strength, but there are no abdominal muscles connected to the leg. You can strengthen your abdominals much more effectively, and much more safely, with other poses.
3. Eka Pada Rajakapotasana (folding forward version)
When it comes to the hip joint, balance is at least as important as openness. When the joint is open in one direction and closed (tight) in another, the imbalance creates postural misalignment of the pelvis, which in turn misaligns the spine.
As mentioned above, most of us sit. A lot. (Or else we have tight hip flexors for some other or additional reason.) Sitting closes the front of the hip joint and opens the back. Folding forward in eka pada rajakapotasana reinforces this pattern of imbalance: the more you lean forward, the more the front of the hip joint closes off, and the more the back of the hip joint is opened.
Yes, it might feel great, but that's not really the standard we should go by. We have to look at the long-term effects of an asana on the body, and we should always be seeking balance. Would I ever do it or teach it? Only if the student can do the full backbend version, tilting the pelvis back enough to comfortably hold the foot. That would indicate the front of the hip joint is also open, and coming forward for a few breaths would be fine. Otherwise, this version of pigeon is just creating greater imbalance in the hip joint.