Objectives: To determine if an end-stage knee osteoarthritis (esKOA) measure, based on symptomatic and radiographic criteria, can indicate progression to severe KOA earlier and with fewer research participants than total knee replacement (TKR). We employed both interventional and observational study designs as examples to estimate the required sample sizes. EsKOA in a knee was declared if either of the following two conditions were met: 1) moderate, intense, or severe symptoms of KOA indicated by pain and disability measurement and severe KOA indicated by radiographically-assessed knee structure; 2) intense or severe symptoms of KOA indicated by pain and disability measurement and frequent knee pain with mild or moderate KOA as indicated by radiographically-assessed knee structure.

Methods: We examined the association between weight loss from baseline to 2-to-2.5-year and 4-to-5-year follow-ups and the odds of esKOA and TKR in 5,593 participants (10,357 knees) from the Osteoarthritis Initiative (OAI) and the Multicenter Osteoarthritis Study (MOST). We also estimated the sample sizes needed for interventional and observational study designs to detect a 10, 20, or 50% reduction in the incidence of esKOA and TKR.

Results: The association of weight loss with both esKOA and TKR was detected at the 4-to-5-year follow-up. However, at the 2-to-2.5-year follow-up, the association was detected for esKOA but not TKR. The required sample sizes for detecting associations of weight loss with the incidence of esKOA were 85% to 93% smaller than those for TKR at the 4-to-5-year and 2-to-2.5-year follow-ups, respectively.

Conclusion: The esKOA measure enables shorter and smaller studies compared to using TKR as an outcome.