Abstract

Purpose Response shift is the phenomenon by which an
individual’s standards for evaluation change over time. The
purpose of this study was to determine whether patients
undergoing autologous chondrocyte implantation (ACI)
experience response shift.
Methods Forty-eight patients undergoing ACI participated.
The ‘‘then-test’’ method was used to evaluate
response shift in commonly used patient-reported outcome
measures (PROMs)—the SF-36 Physical Component Scale
(SF-36 PCS), WOMAC, IKDC, and Lysholm. Each PROM
was completed pre- and 6 and 12 months post-surgery. At
6 and 12 months, an additional ‘‘then’’ version of each
form was also completed. The ‘‘then’’ version was identical
to the original except that patients were instructed to assess
how they were prior to ACI. Traditional change, response
shift adjusted change, and response shift magnitude were
calculated at 6 and 12 months. T tests (p\0.05) were used
to compare traditional change to response-shift-adjusted
change, and response shift magnitude values to previously
established minimal detectable change.