I'm a city girl so I don't understand the term "cow-hocked" so perhaps you can explain that one to me, but after TPOL the leg will be at a new angle permanently and the dog will get used to laying different ways to accommodate the new angle (they can't curl in as tight a ball). I mentally looked at it that surgery as taking a joint in an animal that is weak because it bends slightly and fusing it in the most advantageous position, which requires the "leveling" as represented by the L in the name of the procedure. Our dog held each leg after surgery in a new position, but the paw faced straight ahead which it had not before and I would call her more "bow-legged" by the time we did the two sides, so they use it to correct the direction that foot heads. She had more of an outward swing to her gait after both were done than a dog normally has, or rather, than SHE had prior to the surgery. But it worked fine! That leg is probably already stronger than you realize, as soon as those things knit together, he will have like a "bionic leg"........
edited for typo