Welcome to Justanswer! I am Dr. Altman and happy to assist you both today!
So sorry Cookie is having difficulties with her rear leg
Causes can vary but the most common cause of this change is the knee which can be a patellar luxation or a cruciate or acl tear. Lastly if she is dragging the leg it can be related to her back as well but less likely with her history of having issues with the leg in the past.
Often with a patellar luxation they will occasionally "hop" on walks or going up and down stairs whereas with a partial cruciate tear it can be stiffness after getting up and stretching increased in frequency.
CLICK HERE for information on the patellar luxation
Click here for information on cruciate tears
Ideal is to have your veterinarian evaluate your dog to definitively diagnose the problem and start on appropriate medication to control the discomfort. In addition, they will be able to determine if surgery is warranted to manage the condition. Until you are able to do this please restrict activity (which often they are already doing themselves but that means no steps/ stairs and only carrying to go potty) and rotating warm and cool compresses on the leg in ten minute intervals to reduce pain and increase blood flow.
You can also do light circular massage up and down the leg to stimulate blood flow if this is not too painful and will allow it.
Please let me know if you have any additional questions I can assist with. I hope you are able to get your little one comfortable soon, truly.
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