My left shoulder feels like it is slipping slightly out of joint when I do downward dog. Even if my form is good, I still feel pain. Does anyone know a good variation for the pose that would rotate the shoulder differently?
sssvvvsss,
How are you rotating now? Are you turning your armpits hard toward the floor? Toward one another? Elbows straight? Are you driving your head toward your feet?
The reason why I ask is it’s not just about the shoulder. It’s the whole thing, from the heels of your hands to the heels of your feet. What does your teacher tell you?
Siva
Hello and welcome to the forum,
There are quite a few good threads that address the shoulder in [I]Adho Mukha Svanasana [/I](downward dog) already on the forum. Here is a link to one: Weak Shoulders in DD and you can find plenty more by searching for downward dog and[I] Adho Mukha Svanasana. [/I]This might be a good place to get you started, but as always, please add your own questions to get the information that you need. Adapting to the individual is what keeps us safe in Yoga practice.
Kind regards,
Nichole
For such a simple pose it is a very complex pose 
Welcome to the duality that IS yoga.
In the world of yoga we currently live in there is a surplus of instruction for this pose which is, in fact, completely inaccurate and quite dangerous. I know this will bunch someone’s undergarments so I’ll provide an example.
“Rotate your biceps toward the ceiling”. “Turn your upper arms out.” “Externally rotate the upper arms”. These are very common. The issue here is that the instruction(s) give a seemingly proper result from an absolutely incorrect action. And while that result looks proper the joint suffers over time.
When the only the humerus is rotated externally it IS taken out of the shoulder joint. To then bear weight on that limb is a recipe for joint laxity in an already lax joint. Instead the awareness is moved into the deeper muscle known as the serratus anterior. The humerus is secured into the shoulder joint and the rotation is achieved (as though there’s achievement in yoga - HA!) by contracting or shortening the serratus, thus increasing the space between the medial borders of the shoulder blades.
So in the final pose yes the arms appear in such a way but the action comes not from the rotation of the arm bones but from the contraction of the serratus and the subsequent the abduction of the scapulae. Find a teacher who knows this and you’ve struck gold.
A picture is worth a 1000 words 
Excellent tip InnerAthlete. I tend to bring my attention mostly to my trapezius, infraspinatus and latissimus dorsi. I'll will bring more attention to the serratus tomorrow morning and see how it feels.
Thank you. That is very kind.
Here’s another image worth viewing.
Contracting the lats can actually take the humerus out of the shoulder joint as one of its actions in internal rotation of the humerus.
The trapezius is a large muscle and the actions are split among its fibers. Therefore only the mid to lower fibers actually affect the shoulder blade and its action is retraction not protraction. Even if that were not the case, the upper fibers attach near the occipital ridge therefore tension in the trapezius can adversely affect the neck (for yoga, in Adho Mukha).
The infraspinatus is part of the rotator cuff muscle group and laterally rotates the femur thus stabilizing the shoulder joint. However it does not abduct the scapulae nor is it a very powerful muscle which is why there are three others helping it - supraspinatus, teres minor, subscapularis.
Add to this that the last two muscles are considered superficial rather than deep and you’d see how in this pose, for yoga, they would not bring the most effect nor the most safety.
Finally these three muscles do not build the appropriate actions for Sirsasana, Pincha Mayurasana, Phalakasana (Adho Mukha Dandasana) Chaturanga Dandasana, and Adho Mukha Vrksasana. Now that I think about it, you’re correct. It IS an excellent “tip”.
tried it this morning and it is an excellent tip for me! After a lot of years of weight lifting its easy to get focused on muscles like traps and lats and forget about others like the serratus. I have never been to the gym saying today I’m gonna work on my serratus LOL!!!
Once again thanks for this tip!
[quote=InnerAthlete;16251]
The infraspinatus is part of the rotator cuff muscle group and laterally rotates the femur thus stabilizing the shoulder joint.[/quote]
Leg bone connected to the…that’s very “humerus.” Get it? LOL
I’m not picking on you, but it’s very easy to get lost in this kind of minutia. Focus on this muscle group or that, and you lose the larger picture: how are you directing force/energy?
For example, the slipping you feel in your left shoulder could be what’s going/not going on in your hips and legs. Make sure your legs are rotating inward and your driving your heels down parallel: strong quads, knees straight. What happens when you change the distribution of weight from one foot to the other? You may be driving much harder with the right, or you might be weak in the left. You have to look at the thing as a whole.
Where to focus?
Siva
I’n not suer if the “you” you mention is him or me:-)
I agree with you completely anatomy is useless when it cannot be applied and often it is completely wrong for yoga.
I merely responded to JLG’s points of emphasis in his pose and did so in a rational way so his mind could grasp it. If he had said “I just listen to my heart in the pose and do whatever feels right” I’d have given a different answer.
I’ll further add that focus on how you are directing force or energy would be secondary if you are weight bearing on a limb that is out of joint. You’ll wind up with a lot of time on the recovery table after surgery to contemplate your force.
I don’t know exactly what is going on with the OP’s shoulder. What I do know is SAFETY FIRST!