Title:
Initial validity and reliability of the Banff Patella Instability Instrument.

Abstract:
Patellofemoral instability is a well-recognized problem, but there are currently no published patient-reported quality of life outcome measures that are disease specific for the treatment of this population.
To establish the content validity, initial construct validity, and initial reliability of the Banff Patella Instability Instrument (BPII).
Cohort study (diagnosis); Level of evidence, 2.
The content of the BPII was validated using a modified 3-stage Ebel procedure and analysis of floor and ceiling effects. As a measure of internal consistency, the Cronbach α was utilized to assess how reliably the 32 items of the questionnaire measured a similar construct. Test-retest reliability of the BPII was calculated using an intraclass correlation coefficient (ICC). Construct validity was evaluated on 150 questionnaires completed by patients with a confirmed diagnosis of patellofemoral instability. A one-way between-group analysis of variance was employed to determine if the BPII was able to differentiate between patients presenting at the initial orthopaedic consultation relative to patients presenting at 6 months and 12 months postoperatively.
Content validity was clearly established as each item in the BPII achieved a minimum of 83.3% agreement (range, 83.3%-100%) for relevance among the expert panelists. The average agreement was 96.9%; 24 items achieved 100% agreement. There was no evidence of floor or ceiling effects. Reliability (internal consistency) of the BPII was established at the initial orthopaedic consultation (α = .91), 6 months postoperatively (α = .97), and 12 months postoperatively (α = .97). Test-retest analysis resulted in an ICC of 0.98 between tests. Construct validity was established as there was a statistically significant difference in BPII scores at the initial orthopaedic consultation and 6-month and 12-month postoperative appointments (F2,146 = 75.62; P < .001).
The BPII demonstrates content validity, strong initial reliability, and a statistically significant level of construct validity in patients with patellofemoral instability. This population includes patients with recurrent patellofemoral instability as well as surgically stabilized patients.