Spanish version of the Northwick Park Neck Pain Questionnaire: reliability and validity.
OBJECTIVE
To validate a Spanish version of the Northwick Park Neck Pain Questionnaire (NPQ) and to prove its usefulness in clinical practice.


METHODS
We studied 58 patients with non-inflammatory neck pain of more than 4 months duration. A blind back translation of the NPQ was made, and the resulting back-translation version was then compared with the original. The NPQ comprises 9 questions with 5 statements of increasing difficulty. Patients completed the questionnaire 3 times: on their initial assessment; 8-10 days later (test-retest); and after physiotherapy treatment 3 months later. Neck pain was assessed by a visual analogue scale (VAS).


RESULTS
Fifty-three patients completed the questionnaire (90%). There was a good intra-class correlation between the test-retest NPQ (r = 0.63), indicating good agreement. For each of the 9 sections, agreement ranged from r = 0.43 to r = 0.85, p < 0.05 in all cases. Correlation with the VAS was also good, between r = 0.51 (test) and r = 0.74 (retest) (p < 0.05 in all cases). Pain measured by the VAS increased according to the NPQ score, grouped by percentages (p = 0.003). The mean scores for each section increased with that of the intensity of pain, in most sections showing good internal consistency. Pain and the NPQ score improved after treatment (56.1 +/- 20.2 to 29.9 +/- 20.1, p = 0.0001 and 45.9% +/- 12.7% to 28.9% +/- 15.3%, p = 0.0001 respectively), as did all the other items except for driving (p < 0.05).


CONCLUSIONS
The Spanish version of the NPQ is a feasible, reliable and valid instrument to measure pain in Spanish-speaking patients with chronic neck pain.