Table 1 Classification system for basal joint arthritis of the thumb.

Stage	Radiographic changes
I	Normal TM joint contours with <1/3 joint subluxation
II	TM joint narrowing and osteophytes or loose bodies <2 mm. Instability apparent on stress views. ⩾1/3 joint subluxation
III	TM joint narrowing, subchondral sclerosis, osteophytes or loose bodies >2 mm. ⩾1/3 joint subluxation
IV	Advanced disease of TM and scaphotrapezial joint

TM, trapeziometacarpal.