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The development, validation and internal consistency of the Norwich Patellar Instability (NPI) score

  • Knee
  • Published:
Knee Surgery, Sports Traumatology, Arthroscopy Aims and scope

Abstract

Purpose

No outcome measurements have previously been designed to assess patient-perceived patellar instability. The purposes of this study were to address this limitation and to describe the development and validation of the Norwich Patellar Instability (NPI) scores, a self-administered 19-item questionnaire to assess perceived patellar instability.

Methods

A previous study assessed activities that aggravated symptoms in individuals with patellar dislocation and instability symptoms. These reported activities were ranked in order of severity, and a weighting system was calculated. The NPI score was introduced to routine clinical practice in three institutions. One hundred and two people who had experienced a lateral patellar dislocation completed 102 NPI questionnaires. The completed NPI score was correlated with the Knee injury and Osteoarthritis Outcome Score (KOOS) to evaluate divergent validity and with the J-sign, patellar mobility, apprehension test, Beighton score, Kujala Patellofemoral Disorder Score and Lysholm Knee Score to evaluate convergent validity. Internal consistency of the 19 items was also calculated.

Results

The results indicated a moderate correlation between the NPI score and the Kujala Patellofemoral Disorder Score (rho = −0.66; p < 0.01) and Lysholm Knee Score (rho = −0.54; p = 0.03), suggesting good convergent validity. There was a little correlation between the KOOS and NPI score, indicating divergent validity (rho = −0.02 to −0.17; n.s.). There was high internal consistency (Cronbach’s alpha = 0.93).

Conclusion

These results indicate the NPI score to be a valid tool to assess patellar instability for individuals following patellar dislocation. Further study is now required in order to assess the reliability and responsiveness of this new outcome measure.

Level of evidence

III.

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Acknowledgments

We would like to thank Jo Stephens from the Queen Elizabeth Hospital, Gateshead, UK, and Julie Agel from the University of Minnesota, Minneapolis, USA, for their assistance during the data collection phase of the validation exercise. We would also like to thank Dr Christina Jerosch-Herold from the University of East Anglia, UK, and Julie Agel for their advice during the preparation of this paper. Whilst no licence fee is required before using the NPI score, the developers request that institutions register their use of this score for each patient population or study, by emailing the corresponding author (toby.smith@uea.ac.uk). This study forms part of a PhD undertaken at the University of East Anglia by one author (TS), which has been partly funded by Action Arthritis.

Conflict of interest

None.

Ethical approval

Original epidemiological study—Cambridgeshire 3 Research Ethics Committee (08/H0306/80) and the East Norfolk and Waveney Research Governance Committee (2008PHYS02S (106-08-08). Validation process—No ethical approval was required to adopt this outcome measurement in the UK hospitals. Institutional research board (IRB) approval was sought and gained for its adoption at the University Orthopaedic Clinic, Minneapolis.

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Authors and Affiliations

  1. Queen’s Building, Faculty of Medicine and Health Sciences, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK

    Toby O. Smith, Simon T. Donell, Allan Clark, Rachel Chester & Jane Cross

  2. Norfolk and Norwich University Hospital, Norwich, UK

    Simon T. Donell

  3. Queen Elizabeth Hospital, Gateshead, UK

    Deiary F. Kader

  4. Northumbria University, Newcastle upon Tyne, UK

    Deiary F. Kader

  5. University of Minnesota, Minneapolis, MN, USA

    Elizabeth A. Arendt

Authors
  1. Toby O. Smith
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  2. Simon T. Donell
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  3. Allan Clark
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  4. Rachel Chester
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  5. Jane Cross
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  6. Deiary F. Kader
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  7. Elizabeth A. Arendt
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Correspondence to Toby O. Smith.

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Smith, T.O., Donell, S.T., Clark, A. et al. The development, validation and internal consistency of the Norwich Patellar Instability (NPI) score. Knee Surg Sports Traumatol Arthrosc 22, 324–335 (2014). https://doi.org/10.1007/s00167-012-2359-x

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  • DOI: https://doi.org/10.1007/s00167-012-2359-x

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