Hello I am Dr. Joey. Thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 15 years of experience. I look forward to working with you. I apologize no expert has jumped in to answer your question until now.
Great find to notice the asymmetry. So, this may be nothing to stress over and be a "normal" growth of the bone or even a bony spur as you suggest. Or, it might be something to worry about such as a true bone tumor, although most of the time these are very painful and at least cause some level of lameness. There are other atypical growths we can see that cause bony enlargement, sometimes infection related.
The absolute best step is to have your veterinarian perform and exam to determine if (s)he feels this is indeed abnormal and if so, then, if so, do radiographs (X-rays) that are sent to a board certified radiologist for review. That should give us an answer. It does not sound like this is an emergency such that you must rush in this weekend, unless he is quite painful and is limping. So, it could wait until next week.
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