The reliability, validity and responsiveness of an aggregated locomotor function (ALF) score in patients with osteoarthritis of the knee

Objectives. The aggregated locomotor function (ALF) score, a simple measure of observed locomotor function, using timed walking, stairs and transfers, was developed and evaluated for intra-tester reliability, criterion-related validity and responsiveness in a sample of patients with knee osteoarthritis. Methods. Patients with knee osteoarthritis (n = 214) were recruited for inclusion in a randomized controlled trial investigating two methods of exercise provision. Before treatment, patients completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Short Form 36 health survey (SF-36) questionnaires and were timed whilst performing an 8 m walk, ascending and descending a set of gymnasium stairs and completing a test of transferring in and out of a chair. A group of 15 patients also undertook a replicate test-retest reliability study of the above outcome measures. Standardized response means were calculated for the ALF, WOMAC and SF-36 from data from the clinical trial. Results. The ALF takes 10 min to administer and demonstrated excellent intra-tester reliability, with excellent intra-class correlation coefficient (ICC) statistics (ICC2,k 0.99; 95% CI 0.98-0.99), and low standard error of measurement (0.86 s) and smallest detectable difference (9.5%) values. Criterion-related validity with the physical function dimensions of the WOMAC and SF-36 was good, with correlation coefficients of 0.59 and -0.53 respectively. Standardized response means were higher for the ALF (0.49) than for both the WOMAC (0.39) and the SF-36 (0.12). Conclusions. This work has demonstrated that the ALF can be used as a measure of physical function status and as a means of quantifying treatment response. The measure offers a simple and convenient outcome in the assessment and treatment of locomotor dysfunction. The ALF score is a reliable, valid and responsive outcome measure over 12 months and can be recommended for use in the evaluation of patients with knee osteoarthritis.