Classifications of good versus poor outcome following knee arthroplasty should not be defined using arbitrary criteria.

A recently published paper by te Molder and colleagues in BMC Musculoskeletal Disorders confirmed prior reports indicating that definitions of good versus poor outcome cutoff scores for relevant knee arthroplasty outcomes including pain and function are heterogeneous and that this heterogeneity prevents generalizable inferences. In this Correspondence, we highlight an additional and, in our view, a more important problem with the substantial literature on this topic. There also is high homogeneity in that all studies relied on arbitrarily defined cutoff scores to differentiate good versus poor outcome. We discuss this problem and propose a method to avoid repeating the same problem in future studies designed to group patients into those with good versus those with poor outcome following knee arthroplasty.