Could be pano. Torn ACL in a pup seems a little extreme.
I would want diagnostics performed on my non weight bearing dog before monday. If for anything else just to give him pain meds and relief. I cant imagine a person on here thay would go 4 days without pain meds if their leg hurt so bad they couldnt walk on it. So I would call other day vets in your area and see if they can get you in. Or maybe call your vet and see if they can squeeze him in if you just drop him off for the day. That way they could check him out real fast between their appointments.
Xrays should be done though, IMHO, just to rule out any other bone/joint/soft tissue injury. A torn ACL won't show up on xrays but by manipulating the stifle (knee) a competent vet can easily rule out torn ACL or not.
Panosteitis usually causes a fever in dogs as well so that could be a good indicator. Doesn't always show up on xrays though.
If it is pano, then an NSAID like Carprofen (Rimadyl) and potentially something like tramadol for pain is really your only option. I've never had a dog so sensitive while teething so sounds like your poor pup may just be really reactive about pain, amplifying his symptoms in his leg.
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