Two-Year Recall Bias After ACL Reconstruction Is Affected by Clinical Result

Recall bias is a systematic error caused by inaccuracy in reporting past health status and can be a substantial methodological flaw in the retrospective collection of data. Little is known about recall bias following anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to evaluate patients' recall bias regarding preinjury knee function at 2 years after ACLR.

Patients undergoing ACLR were enrolled in an institutional ACL registry. Preoperatively and at 2 years postoperatively, patients quantified their preinjury knee function on a scale of 0 to 10 (10 = best). Recall bias was quantified as the difference in the reported preinjury function between the 2 time points. The clinical result of ACLR was evaluated according to the International Knee Documentation Committee (IKDC) Subjective Knee Evaluation score. Patients meeting the minimal clinically important difference (MCID) in the IKDC score were considered to have had a good outcome, while patients who did not reach the MCID were considered to have had failure of treatment. Recall bias was compared between the 2 groups.

Of 2,109 patients enrolled in the registry, 1,219 were included in the study. Patients with a good outcome remembered their preinjury knee function on a 0-to-10 scale to be better than what they reported at baseline, by a mean difference of 0.40 points (95% confidence interval [CI], 0.22 to 0.58 points). The recall bias was stronger for patients with a poor outcome, who remembered their knee function to be worse than reported at baseline, by a mean difference of -0.81 (95% CI, -1.4 to -0.26). The mean difference in recall between the 2 groups was -1.21 (95% CI, -1.74 to -0.67) (p < 0.0001).

The recall bias of preinjury knee function following ACLR was small and not clinically meaningful for the majority of patients. However, patients with a poor outcome had a clinically relevant and significant recall bias.

Our findings suggest that patients with a poor outcome have a substantial recall bias. This has clinical relevance when considering treatment effects of revision surgery, whereby the clinical benefit of the treatment might be affected by recall bias.