Abstract / Summary
Background: Valid interpretation of disease-specific patient-reported outcome measures (PROMs), such as the Banff Patellofemoral Instability Instrument 2.0 (BPII 2.0), requires normative reference standards to enable comparison with posttreatment outcomes. Normative values are essential for activity-based measures such as the Marx Activity Scale (MAS). Purpose: To establish North American reference standards for the BPII 2.0 and the MAS using an age- and ethnicity-representative sample of individuals without a history of knee injury. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A Qualtrics panel was used to gather normative data for both the BPII 2.0 and the MAS. A target sample of 600 participants was distributed across 6 age bands, with equal numbers of men and women. Ethnicity-based stratifications were sought to align with the distributions of the populations of the United States and Canada. Descriptive normative values were generated, and an independent t test compared sexes and an analysis of variance compared ethnicities and age groups. Results: Normative reference standards for the BPII 2.0 and the MAS (n = 659) were established for a North American population aged 13 to 65 years. Patients without a history of knee injury who scored a mean of 77.5/100 on the BPII 2.0 and 7.2/16 on the MAS. The sample closely mirrored the regional ethnic population. No floor or ceiling effects were observed for either PROM. There were no mean sex differences for the BPII 2.0 (men = 77.7 ± 21.6; women = 77 ± 23.6) or for the MAS (men = 7.14 ± 3.82; women = 7.21 ± 3.85). There were BPII 2.0 differences between some mean age stratifications (55-65 years: 82.7 ± 21; 36-45 years: 73.6 ± 22.5; F = 2.23; P = .050), but post hoc testing and effect size were negligible (ie, < 0.2). There were MAS mean differences between 3 age groups (55-65 years: 6.1 ± 3.7; 13-18 years: 7.8 ± 4.1; and 26-35 years: 7.5 ± 3.8), but post hoc testing and effect size calculations indicated these were negligible. Conclusion: This study provides the first North American normative reference standards for the BPII 2.0 and the MAS, enabling clinicians to use standardized comparisons to assess treatment success in patients with lateral patellar instability.