Hello. I'm Dr. Clark and I'm happy that you have asked me to assist you with your child and hope that you can benefit from my many years of helping parents like you.
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Great. Growing pains are very common in kids, boys and girls alike, but are usually limited to just above and below the knees. It is usually a dull ache that is helped by massage and ibuprofen, more often in the evening or after lying down at night, and no one knows the cause.
The fact that his pains have been in his ankle is a bit different than typical growing pains and for that reason I'd have his doctor take a look at him.
A good physical with some limited lab work would be a good idea then.
I'd ask his doctor to do the following blood work just to rule out anything more serious such as rheumatoid arthritis: CBC, Sed Rate, CRP and also a urine analysis.
This will rule out lots of things that I'm sure have crossed your mind as you likely have consulted the infamous Dr. Google, which is always a bid Idea for parents!
Xrays are not really necessary as long as his physical exam and lab work are all normal, which I'm sure will be the case.
Great but so often parents plug in symptoms and then get page after page of links to all kinds of bad information.
Happily you landed on the right website where experts like me can give you good advice based on evidence-based medicine.
No need to hurry home as you can just wait until he can see his regular doctor.