Hand joints without radiographic osteoarthritis maintain their joint space width over 4 years despite what's happening elsewhere in the hand

Objectives We aimed to determine whether hand OA is characterized by systemic cartilage loss by assessing if radiographically normal joints had greater joint space width (JSW) loss over 4years in hands with incident or prevalent OA elsewhere in the hand compared with hands without OA. Methods We used semi-automated software to measure JSW in the distal and proximal IP joints of 3368 participants in the Osteoarthritis Initiative who had baseline and 48-month hand radiographs. A reader scored 16 hand joints (including the thumb base) for Kellgren-Lawrence (KL) grade. A joint had OA if scored as KL >= 2. We identified three groups based on longitudinal hand OA status: no hand OA (KL <2 in all 16 joints) at the baseline and 48-month visits, incident hand OA (KL <2 in all 16 joints at baseline and then one or more joints with KL >= 2 at 48months) and prevalent hand OA (one or more joints with KL >= 2 at baseline and 48months). We then assessed if JSW in radiographically normal joints (KL 0) differed across these three groups. We calculated unpooled effect sizes to help interpret the differences between groups. Results We observed small differences in JSW loss that are unlikely to be clinically important in radiographically normal joints between those without hand OA (n=1054) and those with incident (n=102) or prevalent hand OA (n=2212) (effect size range -0.01-0.24). These findings were robust when examining JSW loss dichotomized based on meaningful change and in other secondary analyses. Conclusions Hand OA is not a systemic disease of cartilage.