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Behind the 'inside of elbow', is the ulnar nerve
- probably it is getting irritated in certain position.
Full and painless movements exclude elbow joint involvement.
There could be minor injury
to ligament, muscle or even a hair-line fracture
Rest to the part helps in early stages.
If you do not improve in 4 or 5 days, you should see a doctor and get examined.
Wishing speedy recovery