The assessment of symptoms and functional limitations in low back pain patients:: validity and reliability of a new questionnaire

Many of the existing low back pain (LBP) questionnaires of function and symptoms have a content of different domains of disability presented as a single sum score, making it difficult to derive changes within a specific domain. The present study describes the development of a clinically derived back-specific questionnaire incorporating both a functional limitation and a symptom scale, with a further subdivision of the symptom scale in separate indices for severity and temporal aspects. The aims of the study were to assess the overall reliability and validity of the new questionnaire, named the Profile Fitness Mapping questionnaire (PFM). A total of 193 chronic LBP patients answered the PFM together with five validated criterion questionnaires. For the internal consistency of the questionnaires, the three indices of the PFM had the highest Cronbach's alpha (0.90-0.95) and all items had item-total correlations above 0.2. The correlation coefficients between the PFM and the back-specific criterion questionnaires ranged between 0.61 and 0.83, indicating good concurrent criterion validity. The best discriminative ability between patients with different pain severities was demonstrated by the functional limitation scale of the PFM. Well centered score distribution with no patient's score at the floor or the ceiling level indicates that the PFM has the potential to detect the improvement or worsening of symptoms and functional limitations in chronic LBP patients. Classification according to the International Classification of Functioning, Disability and health (ICF) of WHO revealed a high degree of homogeneous item content of the symptom scale to the domain of impairments, and of the functional limitation scale to the domain of activity limitations. The present study suggests that the PFM has a high internal consistency and is a valid indicator of symptoms and functional limitations of LBP patients. It offers the combination of a composite total score and the possibility of evaluations within specific domains of disability. Complementary evaluation of test-retest reliability and responsiveness to change is warranted.