Rear fetlock joints “knuckling over”

[Hpacres440p]

Had a calf last year that did it when walking, hind fetlock joint would "knuckle" than "pop" as heels dropped. He went to butcher, hocks got "poppier" as he aged also. Just noticed it on a steer purchased from same herd as the previous calf (1 year old) and now on a totally unrelated 5 month old calf. His half-sister and dam have no issues. The calf has no interest in feed, but is growing beautifully and has minerals available, which he does lick. Nutrition, growth rate, or just dumb luck?

 

[ccr]

Stifle injury?

 

[Hpacres440p]

Both rears. Otherwise walks fine. Almost like he starts a step on his toes then his heels pop down. Stifle wouldn't affect three different unrelated animals, I wouldn't think?