Establishing PASS Thresholds for the Knee Numeric-Entity Evaluation Scale (KNEES-ACL) Questionnaire Following ACL Reconstruction

Layne A. Jessup, Hana Marmura, Kevin R. Willits, Robert L. Litchfield, Alan MJ Getgood, Ryan M. Degen, Dianne M. Bryant

Abstract

Background:

The Knee Numeric-Entity Evaluation Score (KNEES-ACL) is a patient-reported outcome measure tailored to patients with anterior cruciate ligament (ACL) injury or reconstruction (ACLR). Clinically meaningful thresholds have not been established for the KNEES-ACL domains (Problems With Daily Activities, Mental Impact, Stability, Strength and Control, Pain, and Sport and Physical Activity).

Purpose:

To calculate Patient Acceptable Symptom State (PASS) thresholds for each KNEES-ACL domain at pre- and postoperative recovery time points following ACLR.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

This prospective single-center study included patients who had experienced an ACL rupture in the past 2 years. Patients completed the English version of the KNEES-ACL, Knee injury and Osteoarthritis Outcome Score (KOOS), International Knee Documentation Committee (IKDC), and PASS questionnaires at least one of the following time points: preoperative, 2 weeks, 6 weeks, and 3, 6, 9, 12, 18, and 24 months postoperative. KNEES-ACL scores were plotted across time and compared with KOOS and IKDC scores. Patients were classified as being in an acceptable (PASS (+)) or unacceptable (PASS (–)) symptom state using the PASS anchor question. PASS thresholds were calculated for each KNEES-ACL domain score at each time point using 3 methods: (1) mean score of patients reporting PASS (+), (2) 75th percentile score of PASS (+) patients (Tubach method), and (3) receiver operating characteristic (ROC) curve analysis using Youden’s index. Area under the curve (AUC) values with 95% confidence intervals were reported to assess the discriminative ability of the PASS scores to differentiate between PASS (+) and PASS (–) patients.

Results:

A total of 253 patients were included in the study (aged 27.1 ± 11.8 years; 47% female). KNEES-ACL, KOOS, and IKDC scores showed similar improvement trajectories over time. In general, PASS thresholds increased at later postoperative time points for each KNEES-ACL domain. AUC values ranged from 0.51 to 0.89, with acceptable discrimination (AUC ≥ 0.70) achieved between 6 and 12 months across all domains.

Conclusion:

ROC-derived PASS thresholds for KNEES-ACL domains with acceptable discrimination from 6 to 24 months postoperatively are recommended for clinical practice and research. PASS thresholds should be used alongside patient-reported goals, functional testing, and psychological assessments.