Most of the prior research on AKOA was confined to the OAI, which was enriched with people with symptomatic KOA or risk factors for KOA. This was our first endeavor to explore if AKOA is present in a community-based cohort. Furthermore, we sought to confirm our prior findings regarding the incidence of AKOA and its relationship with key risk factors (i.e., age, BMI, blood pressure) [1, 8, 9] and outcomes (total knee replacement) . We found that AKOA represented more than 1 in 7 women with incident KOA. Furthermore, women with AKOA were more likely to have greater age and BMI prior to disease onset and perhaps more likely to receive a subsequent knee replacement. These findings offer the first estimates of the incidence of AKOA among a community-based cohort and confirm associations previously detected among OAI participants.
The pooled estimate of cumulative incidence of AKOA over 5 years was 3.9% in Chingford, which was comparable to the cumulative incidence from the OAI cohort over 4 years (3.5%) . However, the percent of incident KOA attributable to AKOA may be slightly lower in the population-based cohort (15%) than the OAI (22%) . It is unclear if the difference in the proportion of AKOA to incident KOA is attributable to Chingford participants being slightly younger or less obese than those in the OAI, other selection criteria, or the additional year of observation used to define AKOA in the Chingford Cohort (5 vs 4 years). Future endeavors that explore AKOA through cross-cohort collaborations may help explain the difference in proportion of AKOA between cohorts. Regardless, it is alarming that we consistently observe that at least 1 in 7 adults who develop KOA may experience an accelerated onset and progression of disease. The implications of this for clinical trials and epidemiological studies warrants further exploration.
Previously reported risk factors and outcomes related with AKOA in the OAI may be generalizable to a broader population. The current analyses supported prior findings that adults with AKOA are likely to have a greater age and BMI than adults with no KOA . Furthermore, we’ve previously observed that age, and not BMI or blood pressure, was associated with AKOA when compared with typical KOA . Within the OAI, we found a trend that blood pressure may be related to AKOA but post hoc analyses failed to support those findings . Similarly, in the Chingford Cohort, we found no association between AKOA and blood pressure in our meta-analysis. Finally, we observed in Chingford and OAI that adults with AKOA may more frequently receive a knee replacement than their peers.
While the Chingford Cohort offered an excellent opportunity to explore AKOA, it is important to acknowledge several limitations. Firstly, the definition of AKOA was adapted to permit AKOA and typical KOA to develop over 5 years versus 4 years. However, we believed this was acceptable since 98% of people developed AKOA over 3 years in the OAI . Secondly, the inter-observer agreement for radiographic severity was moderate to substantial. While the moderate agreement may increase the chance of misclassification, we believe this had minimal impact on our findings since our results complement prior results from the OAI. Thirdly, we could not determine the precise timing of AKOA and therefore it is unclear how much time elapsed between the onset of AKOA and total knee replacement. This limits our ability to compare the incidence of knee replacements after the onset of AKOA between Chingford and the OAI. We also could only explore 4 risk factors and one outcome in Chingford because we focused on variables that were consistently collected overtime in the OAI and Chingford. Despite this limitation, we showed considerable agreement in the findings between Chingford and OAI. The sample size also limited our ability to explore innovative questions about whether risk factors have different associations between those who develop bilateral or unilateral KOA. Future cross-cohort collaborations may provide a more nuanced understanding of risk factors and outcomes; such as the complex interactions among risk factors, which were observed in the OAI [8, 9] and may be inferred from Table 3.