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Estimation of the patient acceptable symptom state (PASS) threshold for the Banff Patellofemoral Instability
Per Arne Skarstein Waaler1,2, Eivind Inderhaug1,2,3, Thomas Birkenes1,2
1Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway.
Purpose:
There is a paucity of studies reporting patient acceptable symptom state (PASS) thresholds for patient reported outcome measures validated for patellar instability. The aim of this study was to determine the PASS threshold for the Banff Patellofemoral Instability Instrument 2.0 (BPII) following surgery for recurrent patellar instability.
Methods:
Patients who underwent patellar stabilisation surgery between 2013 and 2022 were included if they were ≥16 years of age and had ≥12 months of follow-up. The participants completed the BPII and a dichotomous PASS anchor question. The PASS threshold was then calculated using both the adjusted predictive modelling method and receiver operating characteristic (ROC) analysis.
Results:
Complete data were available for 218 knees of 182 patients, with a median follow-up time of 46 months. The PASS threshold was 62.4 (95% confidence interval [CI]: 58.8-65.9) using the adjusted predictive modelling method, and 66.3 (95% CI: 58.1-80.0) using ROC analysis. Overall, 173 patients (79.4%) reported satisfactory symptom states, while 72.9% and 70.6% achieved the respective PASS thresholds. The adjusted predictive modelling method yielded narrower 95% confidence intervals with minimal threshold variation across different approaches for handling bilateral cases compared to ROC analysis (1.3 vs. 8.1 points).
Conclusion:
The PASS threshold for BPII after patellar stabilisation surgery was 62.4 (out of 100 points). The adjusted predictive modelling method demonstrated superior precision and robustness in the PASS threshold calculation compared with the ROC analysis. This threshold provides a disease-specific reference for clinical decision making and research in patellofemoral instability.
Level Of Evidence:
Level III.
