BMCRI method for measuring cup anteversion after total hip replacement

Abstract

Study design: Prospective clinical study.

Back ground: In total hip replacement the cup placement is critical. Orientation is determined by anteversionand abduction. We have devised a simple geometrical method to calculate anteversion using simple instruments which does not require complicated conversion tables, scientific calculators, trigonometric tables and special x ray equipment.

Objectives: The aim of study is to evaluate the new method in terms of reliability and validity in comparison with other commonly used radiological methods against CT evaluation.

Methodology: In 30 hips of 25 consecutive patients, 13 females and 12 males who underwent primary total hip replacement in our institution, the component version in our method was calculated and compared with CT evaluation of angles. The intra and inter observer reliability were assessed.

Results: Average CT measurement was 23.28 for ante version.We found our method had good correlation with CT calculation with average variability of +/_ 3.9138⁰⁰ in planar anteversionand CT methods had excellent intra and inter observer reliability (C.I. = 0.884 to 0.947&0.866 to 0.963).

Conclusion: Our method is accurate in comparison with CT (P value > 0.05), which does not need any reference tables, conversiontables, scientific calculators, multiple radiation exposures and not time consuming.

Keywords: Abduction; Cup ante version; Reliability; Validity.

Fig. 1

Planar angle of anteversion.

Fig. 2

AP X-ray of the pelvis in neutral plane.

Figs. 3 and 4

Two plain AP radiographs, one focusing on pubic symphysis and another focusing on prosthetic head were taken between 3 to 10 days after surgery. Fig. 3 A-P x-ray centered on Pubic symphysis. Fig. 4 A-P x-ray centered on Prosthetic head.

Fig. 5

Superimposed image on trace paper centering on pubic symphysis.

Fig. 6

Superimposed image on trace paper centering on prosthetic head.

Fig. 7

Tracing the ellipseformed by the mouth of the cup.

Fig. 8

Tracing the cup dome.

Fig. 9

Major Axis (A-B) drawn from the edge of the ellipse.

Fig. 10

Completing the ellipse.

Fig. 11

The size of the ellipse formed in ‘PUBIC SYMPHYSIS CENTERED X-RAY’.

Fig. 12

The increased size of the ellipse (increased short axis) formed on the ‘PROSTHETIC HEAD CENTERED X-RAY’ indicating cup ANTEVERTED.

Fig. 13

L−L’ line = Intertuberosity line.

Fig14

A−B = Major Axis.

Fig. 15

C = center of the Major Axis and the ellipse completed by drawing the other half.

Fig. 16

Interpolated cirlcedrawn from the centre C.

Fig. 17

Half of the Minor axis C-D drawn.

Fig. 18

E-F = Tangential line to ellipse parallel to major axis, O = Point of intersection of EF to the interpolated circle.

Fig. 19

Anteversion, a = α.

Fig. 20

Lewinnek method.

Fig. 21

WIDMER radiological method of calculation of anteversion.

Fig. 22

HASSAN radiological method of calculation of anteversion.

Fig. 23

LIAW radiological method of calculation of anteversion.

Fig. 24

RITHEN radiological method of calculation of anteversion.

Fig. 25

CT method for measurement of anteveersion.

Fig. 26

Full ‘circle face’ of the cup.

Fig. 27

Anteverting cup (forming ‘ellipse’), X = variable point on the circle.

Fig. 28

The change of forming ellipse i.e., anteversion proportionate to changing rotation.

Fig. 29

‘Circle face’ (Sagittal face) of cup with its axis’A’ being perpendicular.

Fig. 30

Coronal face becomes ellipse(anteversion)- axis changes from A to B.

Fig. 31

(0⁰Anteversion).