What Effect Is Really Being Measured? An Alternative Explanation of Paradoxical Phenomena in Studies of Osteoarthritis Progression

Response to ‘Does inflammation predict radiographic progression in hand osteoarthritis?‘ by Li et al

“…The analyses were performed at joint level, not at patient level, by generalised estimating equation, which account for intraperson dependency. We agree with Drs Li and Liu that analyses that explore risk factors for osteoarthritis (OA) progression are prone to null results, as elegantly described by Zhang et al 3. However, based on the fact that statistically significant associations between synovitis and radiographic progression were demonstrated in the current paper, this issue is not relevant.…”

Response to: ‘Correspondence on ‘Risk of venous thromboembolism in knee, hip and hand osteoarthritis: a general population-based cohort study’’ by Lin et al

“…2 Since postoperative immobilisation after knee/hip replacement is an intermediate variable, but not a confounder, between incident knee/hip OA and VTE, we felt it is inappropriate to adjust postoperative duration when the study goal is to assess the total effect of incident knee/hip/hand OA on the risk of VTE. 3 Second, we also agree that postoperative thromboprophylaxis is crucial for reducing VTE after joint replacement. We commented in the discussion section that 'more efforts (eg, early mobilisation following surgery) are still needed to further reduce the risk of VTE after surgery'.…”

Using multivariable Mendelian randomization to estimate the causal effect of bone mineral density on osteoarthritis risk, independently of body mass index

“… 29 Inconsistently with the results of our analysis, some previous studies have provided evidence to suggest that high BMD is related to reduced progression of OA, 30 , 31 although this could be explained by index-event bias, in which conditioning on OA leads to spurious associations between OA risk factors. 32 …”