Thanks for your question.
You are absolutely correct that degenerative changes to this extent are not expected at your age and therefore consideration must be given to other possible causes which would include some type of inflammatory arthritis as well as any infective etiology.
The diagnosis of degenerative changes should not be made based only on x ray changes.
You need to have blood tests for inflammatory markers like ESR and CRP Quantitative as well as tests to look for any inflammatory disorder including tests like rheumatoid factor, anti ccp antibody and ANA.
Advanced imaging like MRI may also give clues regarding the cause.
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