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If it is not related to the spondylosis
he could be having rotator cuff tendinitis
and resultant developing frozen shoulder
, He needs to consult a Rheumatologist/Orthopaedician as he may require an MRI to confirm. Also steroid injections will help in frozen shoulder. Which analgesic is he getting. He needs to avoid motion of that joint if painful. He can continue his analgesic as directed by the Doctor and consult his Orthopaedician. You can apply warm compress on the painful area which will offer relief for now.