Computerized ellipse method for measuring acetabular version after total hip replacement – a precision study using synthetic and real radiographs

Figures & data

Figure 1. Synthetic radiographs with (a) and without (b) the femoral head. Acetabular version was measured using Elliversion. The user can read the version from the upper label.

Figure 2. Post-operative radiograph of a United right total hip arthroplasty. Acetabular version was measured using Elliversion.

Figure 3. Post-operative radiograph of a United left total hip arthroplasty. Acetabular version was measured using Elliversion. In this case, half of the ellipse is not visible, and we could only assume the shape. This results in a bigger difference between the measurements. We defined radiographs of this kind as poor-quality radiographs.

Table I.  Absolute error of measurements for synthetic radiographs using the ellipse and trigonometric methods.

Measurement	Min. error	Max. error	Mean	SD	p-value
Ellipse with femoral head #1 & #2*	0	0.98	0.28	0.21	<<0.01
Trigonometric with femoral head #1 & #2*	0	2.06	0.73	0.45
Ellipse without femoral head #1 & #2	0.01	1.24	0.32	0.21	0.19
Trigonometric without femoral head #1 & #2	0	1.02	0.29	0.19

#1 & #2: We combined the calculated error of the first and second measurements.

*Statistical difference.

Table II.  Absolute difference for the repeated measurements.

Measurement	Min.	Max.	Mean	SD	p-value
Ellipse with femoral head #1 & #2	0.03	1.44	0.33	0.31	0.001
Trigonometric with femoral head #1 & #2	0.06	2.19	0.56	0.43
Ellipse without femoral head #1 & #2	0	0.88	0.24	0.19	0.17
Trigonometric without head #1 & #2	0.01	1.41	0.26	0.28
Ellipse real #1 & #2	0.01	1.89	0.44	0.43
Trigonometric real #1 & #2	0.01	2.11	0.58	0.55	0.12
Ellipse (good*) real #1 & #2	0.01	0.78	0.30	0.24	0.04
Trigonometric (good*) real #1 & #2	0.01	2.11	0.52	0.53

good* = after exclusion of the four poor-quality radiographs.