Pup health issue

[Rudedog]

I bred a litter of pups that are now 10 months old. Three of the pups had joint problems at 6 weeks. After running loose they would become gimp, two in the rear and one pup in the front. They seem to come out of it and I did not worry. Today, my female is gimp in the hind quarters from rabbit hunting. Please give me your take on what happened with these pups. The male I bred to was a very prominent stud hound and the owner said he has never seen this in any of his other litters. The female was one that I bred. Thanks in advance for your answer.