Knee joint sagittal plane movement in cerebral palsy: a comparative study of 2-dimensional markerless video and 3-dimensional gait analysis

Figures & data

Figure 1. The 4 knee-flexion and extension variables selected for the analysis (stance and swing phase in percentage of the gait cycle on the X-axis). 1: Knee flexion at initial contact (0% of the gait cycle) important for step length, which can be limited by hamstring spasticity and/or short hamstring muscles; 2: maximum knee flexion at loading response (0–40% of the gait cycle) manages force absorption; 3: minimum knee flexion in stance (25–75% of the gait cycle) describes degree of crouch; 4: and maximum knee flexion in swing (50–100% of the gait cycle) contributes to foot clearance.

Figure 2. Procedures needed for the estimation of the knee flexion and extension angles with the 2-dimensional markerless video system: image pre-processing calibration (a), segmentation (b), participant-specific multi-segmental model (c), and joint-center tracking (d).

Figure 3. Bland–Altman plot for minimum knee flexion in stance on the left side (2D ML, 2-dimensional markerless; 3D GA, 3-dimensional gait analysis).

Figure 4. Bland–Altman plot for maximum knee flexion in swing on the left side (2D ML, 2-dimensional markerless 3D GA, 3-dimensional gait analysis).

Table 1. Variables, side, and mean angles for the 2-dimensional markerless (2D ML) method and 3-dimensional gait analysis (3D GA)

Gait variables (°)	2D ML	3D GA	Difference				Correlation
	and side	mean (SD)	mean (SD)	mean (95% CI)	p-value^a	95% LoA	coefficient	p-value^b
Knee flexion at initial contact
	Right	26.1 (9.5)	19.1 (9.8)	7.0 (5.0–9.0)	< 0.001	–0.9 to 14.8	0.16	0.5
	Left	26.8 (10.6)	20.6 (8.5)	6.3 (4.2–8.2)	< 0.001	–1.6 to 14.1	0.47	0.05
Knee flexion at loading response
	Right	32.4 (9.5)	26.3 (8.7)	6.1 (4.2–8.0)	< 0.001	–1.1 to 13.4	0.22	0.4
	Left	34.0 (9.3)	27.7 (7.1)	6.3 (4.2–8.2)	< 0.001	–1.6 to 14.1	0.49	0.04
Knee flexion in stance
	Right	17.3 (11.7)	10.6 (12.5)	6.7 (4.9–8.3)	< 0.001	–0.2 to 13.5	–0.19	0.4
	Left	17.5 (9.1)	12.2 (9.1)	5.3 (3.1–7.6)	< 0.001	–3.5 to 14.1	–0.052	0.8
Knee flexion in swing
	Right	60.3 (11.4)	55.4 (9.8)	5.0 (2.7–7.3)	< 0.001	–4.1 to 13.9	0.26	0.3
	Left	59.6 (8.4)	56.4 (7.2)	3.3 (1.3–5.2)	< 0.001	–4.5 to 11.1	0.31	0.2

Mean difference calculated by subtracting the 3D GA angle from the 2D ML angle in degrees (SD, standard deviation; CI, confidence interval; LoA, limits of agreement).

a p-value of the mean difference.

b p-value of the Spearmen correlation coefficient.

Table 2. Comparison of estimates from the 2-dimensional markerless (2D ML) method and 3-dimensional gait analysis (3D GA)

	Gait variables	2D ML	3D GA
	Side	ICC (95% CI)	ICC (95% CI)
Knee flexion at initial contact
	Right	0.85 (0.67–0.94)	0.87 (0.70–0.95)
	Left	0.96 (0.92–0.96)	0.95 (0.89–0.98)
Knee flexion at loading response
	Right	0.83 (0.62–0.93)	0.73 (0.41–0.89)
	Left	0.93 (0.84–0.97)	0.95 (0.89–0.98)
Knee flexion in stance
	Right	0.89 (0.74–0.96)	0.88 (0.73–0.95)
	Left	0.93 (0.85–0.97)	0.97 (0.93–0.99)
Knee flexion in swing
	Right	0.92 (0.82–0.97)	0.90 (0.78–0.96)
	Left	0.94 (0.87–0.98)	0.94 (0.87–0.98)

The 18 participants completed 3 trials for each side.