'arthritically' originates from 'arthritic', ultimately from New Latin/Modern medical formation based on Greek 'arthron' meaning 'joint' plus the suffix '-itis' (in 'arthritis') and English adjectival/adverbial suffixes '-ic' and '-ly'.

'arthritically' changed from the adjective 'arthritic' (formed in English from medical New Latin/Greek roots) and eventually became the adverb 'arthritically' by adding the English adverbial suffix '-ly'.

Initially related to the medical term for joint inflammation ('arthritis'), it evolved into an adjective 'arthritic' describing something affected by arthritis and then into the adverb 'arthritically' meaning 'in an arthritic manner'.