Reliability of principal components and discrete parameters of knee angle and moment gait waveforms in individuals with moderate knee osteoarthritis

Gait measures are used to evaluate change in patients with knee osteoarthritis (OA), but reliability has not been fully established in this population. This study examined test-retest reliability of knee angle and moment gait waveform characteristics captured using discrete parameters and principal component analysis (PCA) in individuals with moderate knee OA. Participants (n=20) underwent three-dimensional gait analysis on two occasions. Motion and force data were captured using two camera banks, infrared light emitting diodes and force plate during self-selected walking. Knee angle and moment waveforms were calculated and analyzed using discrete parameters and by identifying waveform characteristics using PCA. Intraclass correlation coefficients (ICC2,k) examined test-retest reliability of discrete parameters and PCA derived scores (PC-scores). ICC2,k values ranged from 0.57 to 0.93 for discrete parameters, 0.52-0.86 for knee angle PC-scores and 0.30-0.94 for the knee moment PC-scores. However, 10 of 13 discrete parameters, six of nine knee angle PC-scores and seven of nine knee moment PC-scores had ICC2,k values greater than or equal to 0.70. Discrete parameters and PC-scores from flexion angles and adduction moments had the highest ICC2,k values while adduction angles, rotation angles, and rotation moments had the lowest. Most knee angle and moment waveform characteristics demonstrated ICC2,k values that could be interpreted as acceptable. Caution should be used when examining adduction and rotation angle magnitudes and early/mid-stance rotation moment magnitudes due to lower ICC2,k values.