Ambulant adults with spastic cerebral palsy: The validity of lower limb joint angle measurements from sagittal video recordings

BackgroundIn the development of a clinical program for ambulant adults with cerebral palsy (CP), we investigated the validity of joint angles measured from sagittal video recordings and explored if movements in the transversal plane identified with three-dimensional gait analysis (3DGA) affected the validity of sagittal video joint angle measurements.MethodsTen observers, and 10 persons with spastic CP (19-63 years), Gross Motor Function Classification System I-II, participated in the study. Concurrent criterion validity between video joint angle measurements and 3DGA was assessed by Bland-Altman plots with mean differences and 95% limits of agreement (LoA). Pearson's correlation coefficients (r) and scatter plots were used supplementary. Transversal kinematics ≥2 SD from our reference band were defined as increased movement in the transversal plane.ResultsThe overall mean differences in degrees between joint angles measured by 3DGA and video recordings (3°, 5° and −7° for the hip, knee and ankle respectively) and corresponding LoA (18°, 10° and 15° for the hip, knee and ankle, respectively) demonstrated substantial discrepancies between the two methods. The correlations ranged from low (r = 0.39) to moderate (r = 0.68). Discrepancy between the two measurements was seen both among persons with and without the presence of deviating transversal kinematics.ConclusionQuantifying lower limb joint angles from sagittal video recordings in ambulant adults with spastic CP demonstrated low validity, and should be conducted with caution. This gives implications for selecting evaluation method of gait.

► We studied concurrent validity of joint angles measured from video screens. ► Quantifying joint angles from a video recording demonstrated its shortcomings. ► This gives implications for selecting evaluation method of gait. ► We suggest that a qualitative approach is preferable for the video-analysis. ► Continuous quantitative data should be derived from other methods.