Raynaud`s phenomenon can either be primary (no specific causes) or secondary to many other diseases.
Some connective tissue
disorders like SLE, Rheumatoid Arthritis
etc are seen associated with raynaud`s phenomenon.
Since you say he has swelling of joints, connective tissue diseases have to be ruled out.
Along with X ray, he might need some blood tests like a complete blood count
, CRP, ESR, Autoantibody
screening, Renal function etc.
You have not mentioned the details of the blood reports.
Please feel free with blood reports and x ray findings too.
Wish you son good health.