My BT has this problem too. So far it's just I mild case worse on the right than the left. My vet says eventually over time he will have to have surgery on the right knee. The patella can pop in and out of socket. My vet also recommended glucosamine chondroitin when it does worsen to lubricate the joints (just like humans take). I have tried to restrict how much by BT jumps up and down off the bed and furniture and that has really helped along w/regular walks

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Juan Pablo