| I |
Synovitis phase, slight widening of the joint space (joint capsule distension), normal articular contours; less than 1/3 subluxation in any projection |
| II |
Significant capsular laxity, at least 1/3 subluxation of the joint; small bone or calcific fragments < 2 mm in diameter are present, usually adjacent to the volar or dorsal facets of the trapezium |
| III |
Greater than 1/3 subluxation; fragments > 2 mm are present dorsally or volarly, usually in both locations; slight joint space narrowing |
| IV |
Advanced degenerative changes; major subluxation and very narrow joint space, with cystic and sclerotic subchondral bone changes; the margins of the trapezium show lipping and osteophyte formation, and there is significant erosion of the dorsoradial facet of the trapezium |
