Response shift in self-reported functional scores after knee microfracture for full thickness cartilage lesions.

OBJECTIVE: Our aim was to determine whether response shift (RS), a change in the internal standards of a patient, occurs in patients treated for full thickness knee cartilage defects. We have also evaluated the effect of functional scores on patient satisfaction after surgery.
DESIGN: Self-administered questionnaires were used to evaluate pre- and post-operative and retrospective post-operative scores of 53 patients following knee microfracture. Patient satisfaction, Lysholm, Visual Analogue Scale (VAS) for pain and modified International Knee Documentation Committee (IKDC) scores were evaluated. RS (pre-test-then-test), unadjusted and adjusted treatment effects (UTE and ATE) and their effect sizes were calculated.
RESULTS: All four functional outcome measures had a positive RS. The effect size of the RS ranged from around 0.35 for the Lysholm and IKDC2 score to over 0.9 for the VAS pain score. Gender, age, smoking status and time since follow-up did not significantly affect the RS. RS did not differ significantly between the three patient satisfaction groups (P>0.05). Post-operative Lysholm and IKDC1 scores differed most significantly between the satisfaction groups.
CONCLUSIONS: All four scores had a significant shift, implying that patients thought they felt worse before the operation in retrospect than they did at the time. The traditional way of assessing treatment effect, difference between post-intervention and pre-intervention functional scores, may be confounded by change in the internal standards of the patient and should take this into account. RS did not affect the clinical interpretation in this case series. Patient-reported satisfaction after surgery is only related to post-operative scores.