We all hear about horses getting their hocks injected. I believe that the main reason for this is from trying to force them to stand 'straight'. The age old standard is that horses are supposed to stand with hind legs facing straight forward. But when you start to understand the proper bone structure, this is not right. 

Most horses stand naturally toed out.

Why? If you look at these horses they all stand with their stifle wider than their point of buttock. I believe this is normal for most horses. Therefore they should stand with their legs pointing the same way as their femur. This is actualy correct if you are balancing to the bone structure.

If you look at the horse from behind, the pelvic bones are the widest point (H). From this point they narrow to the point of the buttocks (B). From there they widen back out to the stifle joint (S).

This tells you that the leg and foot should be at the same angle as the femur. This means the cannon bone and foot should be at the same angle.

This illustrates femur, tibia, and cannon all in alignment.

This is a good example of hind leg high on inside turning foot to inside.
This is the same foot centered with leg. Shows balance and suport of bone column.

(Hind legs both high on the inside)

Farriers have been told to leave back hooves high on inside to make them stand straight (toes facing straight forward).

This is devastating to the horse. It puts pressure on the pastern, fetlock, and hock. I have seen horses with hock problems come sound just by balancing their feet to the cannon bone (using the t-square).

This is a balanced foot. This should be done front and hind.

I believe that hock injections could almost be eliminated by proper trimming and shoeing.