To determine the possible relevance of intra-articular pressure in the
production of ulnar drift, metacarpophalangeal joints of fresh cadaver
specimens were injected with water to increase the intra-articular
pressure. Of the thirty-two joints tested, ulnar deviation was produced in
twenty-three, flexion in twenty-four, and simultaneous ulnar deviation and
flexion (ulnar drift) in nineteen. In two or three instances, the
displacement was in extension or radial deviation. These results suggest
that elevated intra-articular pressure may be a factor in the initiation of
ulnar drift in patients with rheumatoid arthritis.