28 September 2023

Is hand OA systemic or localised?


Researchers investigating radiographically normal joints in people with hand osteoarthritis have concluded that hand OA is not a systemic disease of cartilage.

The team compared joint space width [JSW] loss in unaffected joints over four years among people with incident or prevalent OA and without hand OA and found only small differences that were unlikely to be clinically important.

“[We] found no evidence among radiographically normal joints that hand osteoarthritis is a systemic disease of cartilage,” wrote the authors in Rheumatology.

“The onset of osteoarthritis at one or more joints elsewhere in the hand did not elicit JSW changes in radiographically normal joints. Furthermore, people who had prevalent hand osteoarthritis had similar rates of JSW loss in radiographically normal joints than those without hand osteoarthritis.

“Local conditions (e.g. aberrant joint loading) may be needed to elicit cartilage loss in a susceptible joint.”

The US multicentre cohort study involved analysing radiographs from over 3000 participants in the Osteoarthritis Initiative to determine changes between visits at baseline and four years. Joints were graded using a Kellgren-Lawrence grading scale to determine radiographic severity and JSW was measured for distal interphalangeal and proximal interphalangeal joints at both time points.

Three groups of patients emerged: around 1000 people with no hand OA at both visits, around 100 with incident hand OA (those who developed it between baseline and four years) and 2200 with prevalent hand OA.

Researchers calculated the average joint space and frequency of meaningful change in JSW among the radiographically normal joints for each group.

The average change in JSW in normal joints across all participants for all joints ranged from ‑0.018mm (loss) to 0.057mm. The effect sizes comparing those with incident or prevalent hand OA to those with no hand OA at either visit ranged from -0.01 to 0.24, which the authors described as a small effect. The frequency of meaningful change in JSW was similar across the three groups.

The findings are contrary to a widely held conceptualisation of hand OA as a systemic disease with patients predisposed to general cartilage loss.

The study authors reported previously finding that people with hand OA had narrower JSW in radiographically normal joints than people without hand OA, leading them at the time to conclude it was systemic.

There were some limitations to the study. The authors pointed out that changes in JSW can be bidirectional: JSW can decrease due to cartilage loss or increase due to excess fluid within the articular cartilage.

“Future studies must grapple with the challenge of analysing hand JSW if both an increase or decrease in hand JSW represents pathologic changes,” they suggested.

Another potential limitation was that the Osteoarthritis Initiative study cohort was not representative of the general population as it included people with or at risk of knee OA. They also relied on a single hand joint to define incident OA, so didn’t account for distinct hand OA endotypes, such as thumb-base OA or distal interphalangeal OA.

The authors suggested that the findings could have an impact on future research.

“While contrary to our hypothesis, these findings are clinically intuitive and have important implications for hand osteoarthritis research,” they wrote.

“For example, investigators performing future clinical trials focused on structure modification – such as preventing the onset of osteoarthritis in hand joints – may find that recruiting people with at least one affected hand joint may fail to enrich the study sample for people likely to progress within the next 4 years.”

Rheumatology 2023, online 11 September