Factor analysis of the North American Spine Society outcome assessment instrument: a study based on a spine registry of patients treated with lumbar and cervical disc arthroplasty.

Aghayev, Emin; Elfering, Achim; Schizas, Constantin; Mannion, Anne F. (2014). Factor analysis of the North American Spine Society outcome assessment instrument: a study based on a spine registry of patients treated with lumbar and cervical disc arthroplasty. Spine Journal, 14(6), pp. 916-924. Elsevier 10.1016/j.spinee.2013.07.446

[img] Text
1-s2.0-S1529943013013673-main.pdf - Published Version
Restricted to registered users only
Available under License Publisher holds Copyright.

Download (219kB) | Request a copy

Background context
Studies involving factor analysis (FA) of the items in the North American Spine Society (NASS) outcome assessment instrument have revealed inconsistent factor structures for the individual items.

This study examined whether the factor structure of the NASS varied in relation to the severity of the back/neck problem and differed from that originally recommended by the developers of the questionnaire, by analyzing data before and after surgery in a large series of patients undergoing lumbar or cervical disc arthroplasty.

Study design/setting
Prospective multicenter observational case series.

Patient sample
Three hundred ninety-one patients with low back pain and 553 patients with neck pain completed questionnaires preoperatively and again at 3 to 6 and 12 months follow-ups (FUs), in connection with the SWISSspine disc arthroplasty registry.

Outcome measures
North American Spine Society outcome assessment instrument.

First, an exploratory FA without a priori assumptions and subsequently a confirmatory FA were performed on the 17 items of the NASS-lumbar and 19 items of the NASS-cervical collected at each assessment time point. The item-loading invariance was tested in the German version of the questionnaire for baseline and FU.

Both NASS-lumbar and NASS-cervical factor structures differed between baseline and postoperative data sets. The confirmatory analysis and item-loading invariance showed better fit for a three-factor (3F) structure for NASS-lumbar, containing items on “disability,” “back pain,” and “radiating pain, numbness, and weakness (leg/foot)” and for a 5F structure for NASS-cervical including disability, “neck pain,” “radiating pain and numbness (arm/hand),” “weakness (arm/hand),” and “motor deficit (legs).”

The best-fitting factor structure at both baseline and FU was selected for both the lumbar- and cervical-NASS questionnaires. It differed from that proposed by the originators of the NASS instruments. Although the NASS questionnaire represents a valid outcome measure for degenerative spine diseases, it is able to distinguish among all major symptom domains (factors) in patients undergoing lumbar and cervical disc arthroplasty; overall, the item structure could be improved. Any potential revision of the NASS should consider its factorial structure; factorial invariance over time should be aimed for, to allow for more precise interpretations of treatment success.

Item Type:

Journal Article (Original Article)


04 Faculty of Medicine > Pre-clinic Human Medicine > Institute for Evaluative Research into Orthopaedic Surgery
07 Faculty of Human Sciences > Institute of Psychology > Work and Organisational Psychology

UniBE Contributor:

Aghayev, Emin, Elfering, Achim


600 Technology > 610 Medicine & health
100 Philosophy > 150 Psychology
300 Social sciences, sociology & anthropology


1529-9430, 1878-1632






Diana Cristina Romano

Date Deposited:

25 Mar 2015 10:04

Last Modified:

02 Mar 2023 23:26

Publisher DOI:


Additional Information:

On behalf of the SWISSSpine Registry Group

Uncontrolled Keywords:

NASS, Outcome, Total disc arthroplasty, SWISSspine, Factor analysis





Actions (login required)

Edit item Edit item
Provide Feedback