Psychometric properties of the Norwich Patellar Instability Score in people with recurrent patellar dislocation

T O Smith; A Choudhury; R Navratil; C B Hing

doi:10.1016/j.knee.2019.10.021

Psychometric properties of the Norwich Patellar Instability Score in people with recurrent patellar dislocation

Knee. 2019 Dec;26(6):1192-1197. doi: 10.1016/j.knee.2019.10.021. Epub 2019 Nov 23.

Authors

T O Smith¹, A Choudhury², R Navratil³, C B Hing²

Affiliations

¹ Nuffield Department of Rheumatology, Orthopaedics and Musculoskeletal Sciences, Botnar Research Centre, University of Oxford, Windmill Road, Oxford, UK. Electronic address: toby.smith@ndorms.ox.ac.uk.
² Department of Trauma and Orthopaedics, St George's Hospital, St George's University Hospitals NHS Foundation Trust, Tooting, London, UK; St George's University of London, Tooting, London, UK.
³ Department of Trauma and Orthopaedics, St George's Hospital, St George's University Hospitals NHS Foundation Trust, Tooting, London, UK.

PMID: 31767513
DOI: 10.1016/j.knee.2019.10.021

Abstract

Background: Patellar dislocations account for two percent of all knee injuries with a 17% chance of re-dislocation. There are few validated scores specific to instability. One of these is the Norwich Patellar Instability Score. There has been limited assessment of the validity, floor-ceiling effect and responsiveness of the Norwich Patellar Instability (NPI) Score from an independent centre. The purpose of this paper is to address this limitation.

Methods: Data from 90 patients referred to a tertiary referral patellofemoral clinic were analysed. All routinely completed data including NPI Score, Kujala Patellofemoral Disorder Score, and demographic outcomes during appointments, up to 36 months following initial clinical assessment was analysed. Convergent validity was assessed by correlating outcomes of the Kujala Patellofemoral Disorder Score to the NPI Score. Effect size (ES) was determined between baseline to 12-month and 12 to 36-month assessments to determine responsiveness. Floor-ceiling effect was evaluated at baseline, 12-month and 12 to 36-month follow-up.

Results: NPI Score demonstrated good convergent validity to the Kujala Patellofemoral Disorder Score (p < .001; 95% confidence interval (CI): -0.71 to -0.52). NPI Score demonstrated good responsiveness to change both between baseline to 12 months (ES: 0.43; 95% CI: 0.42 to 0.10) and 12 to 36 months (ES: 0.67; 95% CI: 0.60 to 0.15). Whilst the NPI Score did not demonstrate a ceiling effect, there was moderate risk of a floor-effect where 13% of the cohort reported the lowest levels of NPI scores.

Conclusions: The NPI Score is a valid and responsive outcome for people with recurrent patellar dislocation.

Keywords: Floor-ceiling; Patellar dislocation; Patient-reported outcome measure; Responsiveness; Subluxation; Validity.

MeSH terms

Adolescent
Adult
Cohort Studies
Female
Humans
Joint Instability / complications
Joint Instability / diagnosis*
Joint Instability / psychology*
Male
Patellar Dislocation / etiology
Patellar Dislocation / psychology*
Patellar Dislocation / therapy*
Patellofemoral Joint*
Patient Reported Outcome Measures
Psychometrics
Young Adult