Total knee replacement; minimal clinically important differences and responders.
OBJECTIVE
To provide new data on minimally clinical important difference (MCID) and percentages of responders on pain and functional dimensions of Western Ontario and McMaster Osteoarthritis Index (WOMAC) in patients who have undergone total knee replacement (TKR).


METHODS
1-year prospective multicentre study with two different cohorts. Consecutive patients on the waiting list were recruited. There were 415 and 497 patients included. Pain and function were collected by the reverse scoring option of the WOMAC (0-100, worst to best). Transition items (five point scale) were collected at 1-year and MCID was calculated through mean change in patients somewhat better, Receiver Operating Characteristic (ROC) and two other questions about satisfaction. Analysis was performed in the whole sample and by tertiles of baseline severity. Likewise were calculated the percentages of patients who attained cut-off values.


RESULTS
Global MCID for pain were about 30 in both cohorts and 32 for. By ROC these values were about 20 and 24 respectively. According to the other two transitional questions these values were for pain 27 and 20 for function. By tertiles the worst the baseline score the higher the cut-off values. Percentage of responders does not change when comparing responders to the global MCID with their own tertile MCID and were about 61% for pain and 50% for function.


CONCLUSION
Due to the wide variations, MCID estimates should be calculated and used according to the baseline severity score.