My Golden had the same symptoms Kiki. He just got up one morning and his joint was all swollen and could hardly walk on it. Took him in and the vet did a lymes and something else (I can't remember the name, sorry) that they can get from ticks. While it tested negative for lymes it did however test positive for the other. Even though he was on Advantix, the medicine has no affect on stopping what ever the other thing is that ticks can pass onto animals. Vet game him medicine and within a couple of days it was getting better.
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