Cartilage loss in unaffected ‘healthy’ joints support systemic nature of hand OA
TORONTO — Measuring joint space width as a surrogate for cartilage thickness provided researchers with some evidence that hand osteoarthritis impacts all joints in the hand systemically, and not just the joints that have radiographic evidence of the disease, according to findings presented here.
Immanuel Onuoha, a research assistant at Brigham & Women’s Hospital, raised the simple clinical question that drove the researchers to conduct the study, “Are healthy joints really healthy?”
Onuoha told attendees at the OARSI 2019 World Congress on Osteoarthritis that unlike hip or knee OA, hand OA is assessed at many joints, and not just a single joint. This, then, begs another clinical question about hand OA: “Is it systemic or does it affect individual joints?” he said.
The researchers aimed to test the hypothesis that patients with generalized hand OA will have less cartilage thickness, not only in the joints that have radiographic OA, but also in their seemingly unaffected joints.
“We wanted to investigate cartilage thickness as a systemic factor of hand OA,” Onuoha said. “We used [joint space width (JSW)] as a surrogate for cartilage thickness.”
The researchers used a custom software to assess joints in fingers 2 through 5. They assessed JSW in the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP). The software has a reader that places one set of landmarks that indicate the joint region, another set of landmarks are placed at 25% and 75% of the joint width, and then places markers distally and proximally. “JSW is defined as the distance between these delineated margins,” Onuoha said, or an average of the measurement region.
“We found that if you divide this measurement region into five sub-regions, you can determine the relevance for different sub-regions in the different joint types,” Onuoha said. He added that sub-regions 1 through 5 are most relevant for PIP and DIP, while sub-regions 2 through 4 are relevant for the MCP.
The case-control study included 479 patients with interphalangeal OA and the same number of controls without OA. Cases and controls were matched by age and gender, according to Onuoha.
The study was a joint-level analysis which excluded joints of OA patients with a KL score of 2 or greater, and only assessed the so-called “healthy” joints of those patients. The full data set included 9,463 joints examined out of a possible 11,496 joints.
According to study results of all joints that underwent evaluation, the JSW average among cases was 1.305 mm, compared with 1.391 mm for controls. This was a difference of 6.4% (P < .001). In terms of individual joints, the average thickness of MCP were 1.769 mm in cases and 1.840 mm in controls, for a difference of 4.0% (P < .001). PIP thickness measurements were 1.184 mm in cases and 1.266 mm for controls, for a difference of 6.7% (P < .001). For DIP, cases were 0.962 mm and controls were 1.067 mm, which led to a difference of 10.3% (P < .001).
“We see that we have less DIPs than PIPs, and less PIPs than MCPs,” Onuoha said. “We expect that this is in line with the disease, because the disease affects the more distal joints.”
Onuoha added that the percent difference grows moving upwards along the hand. “This is also in line with what we expect from the disease,” he said. “We expect that there would be more narrowing in cases than controls.”
These findings provide a new understanding of the systemic nature of hand OA, which is cartilage thickness, Onuoha concluded. “This study also further validated the JSW software method,” he added. —by Rob Volansky
Onuoha I, et al. Abstract #34. Presented at: OARSI 2019 World Congress on Osteoarthritis; May 2-5; Toronto, Canada.
Disclosure: Onuoha reports no relevant financial disclosures.