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to muscle, ligament and/or joint capsule is common in such situation..
However, an X-ray is necessary to exclude fracture
MRI will pin point the problem - should be done, if you don't improve..
You have not stated your age, gender, personal habits, family history or co-morbidities
See an orthopaedician
Rest to the part (Splinting if necessary & avoiding weight bearing) is important
Non Steroidal Anti Inflammatory Drugs like ibuprofen
reduce pain & inflammation
compress in first days / later warm compress - help
Wishing speedy recovery