The psychometric properties of Functional Gait Assessment (FGA) in assessing walking ability in people with knee osteoarthritis.

OBJECTIVE

(1) Compare Functional Gait Assessment (FGA) scores between knee osteoarthritis (KOA) patients and healthy older adults; (2) assess FGA inter-rater/test-retest reliability in people with KOA; (3) examine the correlations between FGA scores and knee function measures; (4) identify the optimal FGA cutoff score for distinguishing people with KOA from healthy controls.

METHODS

This cross-sectional study included 63 individuals with KOA (mean age = 66.6 years) and 30 healthy older adults (mean age = 68.1 years). The participants were assessed by FGA, knee flexion/extension strength, Limit of Stability (LOS), Berg Balance Scale (BBS), Timed Up and Go (TUG), Five Times Sit to Stand (5STS), Activity-specific balance confidence (ABC) scale, Knee Injury and Osteoarthritis Outcome Score (KOOS), Falls Efficacy Scale-International (FES-I), and Oxford Participation and Activities Questionnaire (Ox-PAQ). The KOA group was assessed on Day 1 and Day 2 (7 days apart), whereas the healthy group was assessed on Day 1 only. Inter-rater and test-retest reliability of the FGA in the KOA group were evaluated using the Intraclass Correlation Coefficient (ICC). Correlations between FGA performance and other outcome measures were analyzed using Pearson's r or Spearman's rho. The optimal FGA cutoff score for differentiating between the KOA and healthy groups was determined using the Receiver Operating Characteristic curve.

RESULTS

People with KOA (mean ± standard deviation (SD) = 23.49 ± 3.87) had significantly lower(p < 0.001) FGA scores than healthy older adults (mean ± SD = 27.03 ± 2.51). The FGA demonstrated excellent inter-rater reliability (ICC = 0.986) and good test-retest reliability (ICC = 0.897). FGA scores showed moderate-to-strong positive correlations with affected knee strength, LOS, BBS, KOOS, and ABC (r = 0.36-0.70), and significant negative correlations with TUG, 5STS, FES-I, and Ox-PAQ scores (r = -0.32 to -0.69). The optimal FGA cutoff score was 25.5 (Area Under the Curve = 0.795-0.798, sensitivity = 0.867, specificity = 0.651-0.667) as a threshold to distinguish performance of people with KOA from healthy controls.

CONCLUSION

The FGA showed promising overall reliability and selected validity evidence in this sample, while further confirmation in larger, more diverse cohorts is required.