Secondary hip dysplasia increases risk for early coxarthritis after Legg-Calve-Perthes disease. A study of 255 hips

Figures & data

Figure 1. Anteroposterior and axial radiograms of the patient after right-sided LCPD with obvious flattening of the articular surface in the anteroposterior direction; r represents the radius of the contour of the articular surface in the frontal plane, and r−δ represents the semiaxis of the elliptical contour in the sagittal plane. The axial radiograms were rotated to the extent that the vertical semiaxis of the ellipse in the sagittal plane (r, r−δ) was parallel to the horizontal semiaxis of the circle in the frontal plane.

Table 1. Comparison of hips diagnosed with Legg Calve Perthes Disease in childhood and contralateral hips with respect to biomechanical and geometrical parameters.

Parameter	Hips subjected to LCPD in childhood (141)	Contralateral hips (114)	Difference (%)	p
δ	0.192 ± 0.332	0.071 ± 0.125*	83	<10^−3
R	2.81 ± 0.52 cm*	2.46 ± 0.26 cm	13	<10^−9
ϑCE	24.9 ± 13.06 degrees	33.4 ± 7.28 degrees*	−29	<10^−13
WB	814 ± 163 N	804 ± 168 N	1	0.64
pmax	2.50 ± 1.21 MPa	2.28 ± 0.62 MPa	9	0.07
pmax/WB	3124 ± 1968/m^2	3061 ± 2023/m^2	2	0.80
Θ	22.9 ± 13.6 degrees	13.0 ± 7.27 degrees*	55	<10^−10
ϑf	92.0 ± 22.8 degrees	110.4 ± 13.7 degrees*	−18	<10^−12
A	24.8 ± 8.7 cm^2	23.5 ± 5.8 cm^2	5	0.15
Gp	3.84 ± 49.01 MPa/m	−28.94 ± 20.76 MPa/m*	<0	<10^−9
Gp/WB	3196 ± 55036/m^3	−36325 ± 26859/m^3*	<0	<10^−10

An asterisk denotes a more favourable outcome in statistically significant differences. In parameters G_p and G_p/W_B a sign is only given for the % difference, since these parameters can attain positive or negative values.

Table 2. Comparison of hips with frontal radius of the articular sphere larger than 2.65 cm, and hips with frontal radius smaller than 2.65 cm with respect to biomechanical and geometrical parameters.

Parameter	Hips with radius > 2.65 cm (90)	Hips with radius < 2.65 cm (165)	Difference (%)	p
δ	0.272 ± 0.390	0.063 ± 0.111*	125	<10^−9
r	3.09 ± 0.48 cm*	2.40 ± 0.16 cm	25	<10^−41
ϑCE	23.6 ± 10.6 degrees	31.5 ± 7.4 degrees*	−28	<10^−10
WB	858 ± 175 N	782 ± 154 N*	9	<10^−3
pmax	2.47 ± 1.38 MPa	2.36 ± 0.70 MPa	5	0.40
pmax/WB	2930 ± 2324/m^2	3189 ± 1777/m^2	−8	0.32
Θ	25.1 ± 15.0 degrees	14.8 ± 8.4 degrees*	52	<10^−10
ϑf	88.5 ± 25.1 degrees	106.7 ± 15.4 degrees*	−19	<10^−11
A	29.0 ± 9.8 cm^2*	21.6 ± 4.0 cm^2	29	<10^−14
Gp	11.15 ± 52.99 MPa/m	−23.00 ± 28.43 MPa/m*	< 0	<10^−9
Gp/WB	12055 ± 56181/m^3	−29192 ± 36771/m^3*	< 0	<10^−10

An asterisk denotes a more favourable outcome in statistically significant differences. In parameters G_p and G_p/W_Ba sign is only given for the % difference, since these parameters can attain positive or negative values.

Table 3. Comparison of hips subjected to Legg Calve Perthes Disease with frontal radius of the articular sphere smaller than 2.65 cm and contralateral normal hips with frontal radius smaller than 2.65 cm, with respect to biomechanical and geometrical parameters.

Parameter	Hips subjected to LCPD with radius < 2.65 cm (67)	Contralateral hips with radius < 2.65 cm (95)	Difference (%)	p
δ	0.084 ± 0.134	0.048 ± 0.088*	55	0.037
r	2.44 ± 0.13 cm*	2.38 ± 0.18 cm	2	0.016
ϑCE	28.6 ± 7.1 degrees	33.6 ± 6.89 degrees*	−16	<10^−4
WB	774 ± 138 N	789 ± 165 N	−2	0.55
pmax	2.43 ± 0.78 MPa	2.30 ± 0.78 MPa	5	0.23
pmax/WB	3161 ± 1009/m^2	3113 ± 1977/m^2	2	0.86
ϑf	100.9 ± 16.1 degrees	110.85 ± 13.68 degrees*	−9	<10^−4
Θ	17.8 ± 9.3 degrees	12.8 ± 7.1 degrees*	33	<10^−3
A	21.0 ± 3.9 cm^2	22.0 ± 4.1 cm^2	−5	0.123
Gp	−11.93 ± 33.74 MPa/m	−30.84 ± 20.85 MPa/m*	<0	<10^−4
Gp/WB	−14862 ± 43477/m^3	−39330 ± 27268/m^3*	<0	<10^−4

An asterisk denotes a more favourable outcome in statistically significant differences. In parameters G_p and G_p/W_Ba sign is only given for the % difference, since these parameters can attain positive or negative values.

Table 4. Comparison of dysplastic (Gp positive) and nondysplastic (Gp negative) hips according to the HIPSTRESS classification, with respect to biomechanical and geometrical parameters.

Parameter	Dysplastic hips with Gp > 0 (66)	Normal hips with Gp < 0 (189)	Difference (%)	p
δ	0.25 ± 0.40	0.10 ± 0.19*	86	<10^−4
r	3.00 ± 0.60 cm*	2.53 ± 0.31 cm	17	<10^−13
ϑCE	16.42 ± 6.32 degrees	32.99 ± 5.93 degrees*	−67	<10^−50
WB	812 ± 171 N	814 ± 180 N	0	0.92
pmax/WB	3721 ± 1382/m^2	2878 ± 2122/m^2*	26	0.003
pmax	3.08 ± 1.28 MPa	2.17 ± 0.75 MPa*	35	<10^−10
Θ	35.29 ± 9.76 degrees	12.66 ± 6.04 degrees*	94	<10^−60
ϑf	71.16 ± 15.69 degrees	110.38 ± 11.34 degrees*	−43	<10^−59
A	22.0 ± 7.65 cm^2	25.1 ± 7.38 cm^2*	−13	0.005
Gp	38.51 ± 53.13 MPa/m	−28.04 ± 16.74 MPa/m*	< 0	<10^−36
Gp/WB	45171 ± 55560/m^3	−35300 ± 21427/m^3*	< 0	<10^−41

An asterisk denotes a more favourable outcome in statistically significant differences. In parameters G_p and G_p/W_B a sign is only given for the % difference, since these parameters can attain positive or negative values.

Table 5. Comparison of hips with ϑ_CE smaller than 20 degrees and normal hips with ϑ_CE larger than 20 degrees, with respect to biomechanical and geometrical parameters.

Parameter	Hips with ϑCE < 20 degrees (42)	Normal hips with ϑCE > 20 degrees (213)	Difference (%)	p
δ	0.26 ± 0.36	0.10 ± 0.21*	89	<10^−3
r	3.07 ± 0.52 cm*	2.55 ± 0.34 cm	19	<10^−13
ϑCE	13.72 ± 4.64 degrees	31.86 ± 6.49 degrees*	^−80	<10^−43
WB	796 ± 182 N	810 ± 160 N	^−2	0.61
pmax/WB	3721 ± 1382/m^2	2878 ± 2122/m^2*	26	0.003
pmax	3.08 ± 1.28 MPa	2.17 ± 0.75 MPa*	35	<10^−10
Θ	38.54 ± 8.73 degrees	14.27 ± 7.40 degrees*	92	<10^−48
ϑf	65.21 ± 12.88 degrees	107.64 ± 13.34 degrees*	^−49	<10^−59
A	21.72 ± 7.67 cm^2	24.72 ± 7.48 cm^2*	−13	0.020
Gp	53.25 ± 60.83 MPa/m	−24.03 ± 19.72 MPa/m *	<0	<10^−35
Gp/WB	63328 ± 62554/m^3	−29921 ± 25452/m^3 *	<0	<10^−39

An asterisk denotes a more favourable outcome in statistically significant differences. In parameters G_p and G_p/W_B a sign is only given for the % difference, since these parameters can attain positive or negative values.

Table 6. Correlation coefficients and corresponding probabilities between parameters. All hips (255) were considered.

	δ	ϑCE	Θ	ϑf
r	0.73 (p = 0)	−0.49 (0)	0.51 (0)	−0.51 (0)
δ		−0.24 (<10^−4)	0.26 (<10^−4)	−0.26 (<10^−4)

All correlations are statistically significant (p < 0.05).

Figure 2. Correlation between deformation of the articular surface and radius of the femoral head in the frontal plane. Blue crosses pertain to hips subjected to Perthes Disease in childhood and red crosses pertain to control (contralateral) hips.

Figure 3. Correlation between index of stress gradient normalised with respect to body weight G_p/W_Band deformation of the articular sphere δ. Blue crosses pertain to hips subjected to Perthes Disease in childhood and red crosses pertain to control (contralateral) hips.