The primary cause of Ulnar Deviation of the Metacarpal Phalangeal joints (MP) of the fingers, a chronic, irreversible condition, is Rheumatoid Arthritis (RA). The MP joints are a primary site of rheumatoid deformities due to several anatomical and bio mechanical factors. Chief among the factors are:
The shape of the metacarpal head allows for a certain degree of motion in an ulnar direction which contributes to the hands ability to create a strong grip
