The lower limb tasks questionnaire: is it useful in the assessment of function in low back pain sufferers?
Objective: The objective of this study was to investigate selected measurement properties of the Lower Limb Tasks Questionnaire (LLTQ) in a sample of acute Low Back Pain (LBP) subjects, and compare these findings to the Roland Morris Questionnaire (RMQ). The primary aim of the study was to investigate the responsiveness and minimal clinical important difference (MCID) within this population. Additionally, an analysis of the content and construct validity of the LLTQ was undertaken. Study Design: A quantitative prospective evaluation of outcome measures, assessing limitations in physical function change over a course of treatment. Background: Low Back Pain (LBP) is a common condition associated with a loss of function. As restoration of function is a major aim of physiotherapy management and the utilisation of outcome measurements is a fundamental requirement of practice, clinicians must have measures that can detect meaningful change in this construct. The LLTQ is an outcome measure which has been used for populations with lower limb conditions, and in this population it has been shown to demonstrate sound psychometric properties. It offers potential advantages to clinicians and researchers relating to its scoring system, its ability to delineate functional tasks relating to activities of daily life and recreation and to assessing the importance of tasks to the individual. Methods: Sixty nine subjects who presented for physiotherapy treatment with acute LBP completed the LLTQ and RMQ at the initial visit, when a level of ‘improved’ had been reached using a 7 point Global Perceived Effect score (GPE), and at discharge. Statistical procedures included, analysis of importance rating data and correlation analysis between baseline LLTQ and RMQ scores to investigate content and construct validity respectively. Responsiveness was estimated using distribution based analyses of effect size, the standardised response mean (SRM) and the minimal detectable change (MDC) for both measures. An anchor based receiver operating characteristic (ROC) curve was generated to establish best cut off points to estimate the MCID of the LLTQ, and was repeated for variations of baseline scores. Results: The LLTQ was found to cover a wider spread of important functional tasks specifically relating to social, work and employment activities than the RMQ when contrasted with the International Classification of Functioning (ICF) model. A moderate correlation of RMQ scores with both domains of the LLTQ was found (r= .56 and .67), with a significantly stronger correlation demonstrated with the Recreational domain. There was a significant increase in LLTQ scores between the baseline and ‘improved’ level (p<0.05) and baseline and discharge (p<0.05). The measure demonstrated high levels of responsiveness, with an effect size of 1.6 and 1.7 for the ADL and recreational domains respectively and an SRM of 1.5 for both domains. The MDC was 2.5 and 2.1 points respectively for the ADL and recreational domains. The MCID was 3 points for both domains of the measure, with a likelihood ratio over 10. Further analysis demonstrated a significant relationship between lower baseline scores and higher change scores, however an MCID of 3 points was generated for both domains of the measure regardless of baseline score category. Conclusion: The results of this study set important benchmarks regarding the ability of the LLTQ to detect both statistical and clinically meaningful change in an acute LBP population. Through contrasting the measure with an external framework of function and the widely employed RMQ, the LLTQ has been shown to have sound content that reflects the limitations of function and priorities of this population. As a practical, valid and responsive measure that can be applied across various clinical populations, the LLTQ thus has the potential to address issues related to the utilisation of outcome measures by clinicians.