Minimal important change in the Hip Disability and Osteoarthritis Outcome Score and the European Quality of Life 5 Dimensions in adults with hip osteoarthritis after 12 weeks of exercise

Background
Minimal important change (MIC) is the smallest change that can be considered important. In hip osteoarthritis (OA) several measurement instruments are recommended but lack MIC estimates.

Objectives
The objective was to estimate the MIC after supervised group-based exercise for the following measurement instruments; Hip Disability and Osteoarthritis Outcome Score (HOOS), European Quality of Life 5 Dimensions (EQ-5D-5L), 30-s Chair Stand Test, 40-m Fast-paced Walk Test, 9-step Stair Climb Test, Nottingham Leg Extension Power Rig, and unilateral One-Repetition-Maximum Leg Press.

Design
Secondary analysis from a randomized trial of 160 participants with hip OA randomized to two different exercise interventions.

Methods
Participants were assessed using the instruments at baseline and after 12 weeks of exercise. At follow-up the participants also rated their perceived change using a Global Rating of Change Score (GRCS). A correlation of >0.3 between the measurement instruments and the GRCS was a prerequisite for estimating the MIC using the predictive modeling approach.

Results
Only two measurement instruments had acceptable correlations and were included in the MIC analysis. The MIC for the five HOOS subscales ranged from 6 to 10 points (scale range: 0–100). The MIC for the EQ-5D-5L index (scale range: -0.757 to 1) and EQ-VAS (scale range: 0–100) were 0.054 (0.03; 0.08) and 4.83 (1.37; 8.48), respectively.

Conclusions
The reported MIC values indicate the minimal improvement that the average patient with hip OA would consider important after 12 weeks of exercise and will help clinicians and researchers interpret the clinical importance of the results of exercise interventions.