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Factor analysis of the SRS-22 outcome assessment instrument in patients with adult spinal deformity

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Abstract

Purpose

Designed for patients with adolescent idiopathic scoliosis, the SRS-22 is now widely used as an outcome instrument in patients with adult spinal deformity (ASD). No studies have confirmed the four-factor structure (pain, function, self-image, mental health) of the SRS-22 in ASD and under different contexts. Factorial invariance of an instrument over time and in different languages is essential to allow for precise interpretations of treatment success and comparisons across studies. This study sought to evaluate the invariance of the SRS-22 structure across different languages and sub-groups of ASD patients.

Methods

Confirmatory factor analysis was performed on the 20 non-management items of the SRS-22 with data from 245 American English-, 428 Spanish-, 229 Turkish-, 95 French-, and 195 German-speaking patients. Item loading invariance was compared across languages, age groups, etiologies, treatment groups, and assessment times. A separate sample of SRS-22 data from 772 American surgical patients with ASD was used for cross-validation.

Results

The factor structure fitted significantly better to the proposed four-factor solution than to a unifactorial solution. However, items 14 (personal relationships), 15 (financial difficulties), and 17 (days off work) consistently showed weak item loading within their factors across all language versions and in both baseline and follow-up datasets. A trimmed SRS (16 non-management items) that used the four least problematic items in each of the four domains yielded better-fitting models across all languages, but equivalence was still not reached. With this shorter version there was equivalence of item loading with respect to treatment (surgery vs conservative), time of assessment (baseline vs 12 months follow-up), and etiology (degenerative vs idiopathic), but not age (< vs ≥50 years). All findings were confirmed in the cross-validation sample.

Conclusion

We recommend removal of the worst-fitting items from each of the four domains of the SRS-instrument (items 3, 14, 15, 17), together with adaptation and standardization of other items across language versions, to provide an improved version of the instrument with just 16 non-management items.

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Notes

  1. The official Spanish and Turkish versions contained the SRS-22R formulation of item 18, whilst that of SRS-22 was used in all other languages (http://www.srs.org/professionals/online-education-and-resources/patient-outcome-questionnaires).

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Acknowledgements

Funding was provide by Depuy Synthes Spine research Grant.

Author information

Authors and Affiliations

  1. Spine Center Division, Department of Teaching, Research and Development, Schulthess Klinik, Lengghalde 2, 8008, Zurich, Switzerland

    A. F. Mannion & S. Richner-Wunderlin

  2. Institute for Psychology, University of Bern, Fabrikstrasse 8, 3012, Bern, Switzerland

    A. Elfering

  3. Spine Unit, Hospital Universitari Vall Hebron, Passeig Vall Hebron 119-129, Traumatology Building 2nd Floor, 08035, Barcelona, Spain

    J. Bago & F. Pellise

  4. Spine Research Unit, Vall Hebron Institute of Research (VHIR), Passeig Vall Hebron 119-129, Traumatology Building 2nd Floor, 08035, Barcelona, Spain

    A. Vila-Casademunt & M. Domingo-Sàbat

  5. Pellegrin Bordeaux University Hospital, Place Amélie Raba Léon, 33000, Bordeaux, France

    I. Obeid

  6. Ankara Spine Center, Iran Caddesi 45/2, Kavaklidere, 06700, Ankara, Turkey

    E. Acaroglu

  7. Department of Orthopaedics and Traumatology, Acibadem University School of Medicine, Büyükdere cad, 40 Maslak, 344457, Istanbul, Turkey

    A. Alanay

  8. Hospital Universitario La, Paz Paseo de la Castellana 261, 28046, Madrid, Spain

    F. S. Pérez-Grueso

  9. Department of Orthopedics, Washington University School of Medicine, St. Louis, MO, 63110, USA

    C. R. Baldus & K. H. Bridwell

  10. Norton Leatherman Spine Center, 210 East Gray Street, Suite 900, Louisville, KY, 40205, USA

    L. Y. Carreon & S. D. Glassman

  11. Spine Center, Schulthess Klinik, Lengghalde 2, 8008, Zürich, Switzerland

    F. Kleinstück

Authors
  1. A. F. Mannion
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  2. A. Elfering
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  9. E. Acaroglu
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  16. F. Kleinstück
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European Spine Study Group (ESSG)

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Correspondence to A. F. Mannion.

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Mannion, A.F., Elfering, A., Bago, J. et al. Factor analysis of the SRS-22 outcome assessment instrument in patients with adult spinal deformity. Eur Spine J 27, 685–699 (2018). https://doi.org/10.1007/s00586-017-5279-0

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  • DOI: https://doi.org/10.1007/s00586-017-5279-0

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