I had a similar experience with George (my male BTS) when he was about 6 months old (?) initially diagnosed by a vet as a sprain, didn't improve, different vet took xrays and discovered it was a broken bone in his upper left arm, and he was put on pain relief/antiflamatories (IM injections) the break pinned and arm and left shoulder immobilized (all done under a general) , well immobilized much as is possible with a boisterous little juvenile lizard.
Several weeks later, caste removed , arm good as new.
And at about 15 months old Puff was seen to be limping when on the floor , so straight off to the same vet as who fixed George's arm ,and when he placed him on the floor , no more limp .... little bugger was making a liar of me .... his gate was perfect in the presence of the vet and afterwards.
Keep an eye on it, if it doesn't improve in a few days, I think it will be a good idea for a good reptile vet to see him.