How does soft tissue distribution affect anteversion accuracy of the palpation procedure in image-free acetabular cup navigation? An ultrasonographic assessment

Figures & data

Figure 1. Symbolic depiction of geometric (w and o., blue), ultrasonographic measurement (li, r. i., and s. y., red) and geometric calculation (h, green). [Color version available online.]

Figure 2. Exemplary depiction of ultrasound examination of one patient. (a) Static, sagittal B-mode image of the anterior superior iliac spine. In this particular case, the distance from skin to bone measured 10 mm. (b) Static, sagittal B-mode image of the symphysic area. Here, the distance from skin to bone measured 17 mm.

Table I.  Summary of the patients' biometric data, ultrasound measurements, and statistical evaluation referring to misinterpretation of anteversion.

	Unit	Average standard deviation	Maximum	Minimum
(a)
Age	y	64 ± 11	88	36
Body weight	kg	78 ± 15	110	49
Body length	cm	168 ± 8	185	148
Body mass index	kg/m^2	27.7 ± 4.6	37.5	19.2
Distance between both ASIS	cm	25.1 ± 2.2	32.0	21.0
Distance between inter-ASIS line and symphysis	cm	8.6 ± 1.5	12.0	5.4
Soft tissue thickness in front of left ASIS	mm	7.9 ± 3.3	21.0	2.0
Soft tissue thickness in front of right ASIS	mm	7.9 ± 2.4	16.0	2.0
Soft tissue thickness in front of symphysis	mm	13.6 ± 4.1	26.0	6.0
Misinterpretation of anteversion due to soft tissue distribution	°	2.8 ± 1.8	8.0	− 1.2
(b) Misinterpretation of anteversion (°)
Average			2.8
Standard deviation			1.8
Minimum			− 1.2
Maximum			8.0
Median			2.4
Confidence interval of the median (95%)			2.2–3.0

Figure 3. Plots of the individual misinterpretation of anteversion (°) v. s. (a) body weight (kg), (b) body mass index (kg/m²), (c) pelvic width (cm), and (d) height of the triangle defining the frontal pelvic plane (cm). Data of male patients are depicted with black triangles (▴) and female patients with white circles (O).

Table II.  Data describing the earlier plotted correlations (Figure 3a–d).

	Error v. s. weight	Error v. s. BMI	Error v. s. pelvic width		Error v. s. pelvic height
Pearson's correlation coefficient (r)
Male	0.25	0.26	0.50	p = 0.011	− 0.25
Female	− 0.21	− 0.18	− 0.02		− 0.34	p = 0.019
All	0.01	− 0.03	0.20		− 0.30

Note: Misinterpretation of anteversion is simplified as ‘error’.