Correction of Pelvic Tilt and Pelvic Rotation in Cup Measurement after THA – An Experimental Study

Abstract

ZUSAMMENFASSUNGZiel Nach Hüft-TEP-Versorgungen ist die korrekte Vermessung der Pfannenstellung in postoperativen Röntgenaufnah-men wichtig für die Qualitätskontrolle. In dieser Studie stellen wir eine neue Methode vor, mit der wir Messungenauigkeiten, die sich durch die Beckenverkippung und -verdrehung ergeben, korrigieren können.Methode In einem experimentellen Ansatz implantierten wir eine Prothesenpfanne in ein Kunststoffbecken und bestimmten die tatsächliche Pfannenstellung in einer CT. Um die Auswirkung der Beckenverkippung und -verdrehung auf die Pfannenstellung in AP Röntgenbildern darzustellen, wurde das Becken auf einer Halterung fixiert, mit der eine graduelle Vor-und Rückwärts-Kippung (± 15°) sowie eine Beckenverdrehung (0°bis 20°zur Gegenseite) umgesetzt werden konnte. Zur Korrektur von Messfehlern, die sich aus der Beckenverkippung und -rotation ergeben, entwickelten wir gemäß der Definitionen der Anteversion und Inklination nach Murray ein neues Korrekturverfahren, mit dem die Pfannenstellung in einem Becken bezogenen Koordinatensystem (Anterior Pelvic Plane) vermessen werden kann. This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. ABSTR AC TPurpose Accurate assessment of cup orientation on postoperative pelvic radiographs is essential for evaluating outcome after THA. Here, we present a novel method for correcting measurement inaccuracies due to pelvic tilt and rotation.Method In an experimental setting, a cup was implanted into a dummy pelvis, and its final position was verified via CT. To show the effect of pelvic tilt and rotation on cup position, the dummy was fixed to a rack to achieve a tilt between + 15°a nterior and -15°posterior and 0°to 20°rotation to the contralateral side. According to Murray's definitions of anteversion and inclination, we created a novel corrective procedure to measure cup position in the pelvic reference frame (anterior pelvic plane) to compensate measurement errors due to pelvic tilt and rotation.Results The cup anteversion measured on CT was 23.3°; on AP pelvic radiographs, however, variations in pelvic tilt (± 15°) resulted in anteversion angles between 11.0°and 36.2°(mean error 8.3°± 3.9°). The cup inclination was 34.1°o n CT and ranged between 31.0°and 38.7°(m. e. 2.3°± 1.5°) on radiographs. Pelvic rotation between 0°and 20°showed high variation in radiographic anteversion (21.2°-31.2°, m. e. 6.0°± 3.1°) and inclination (34.1°-27.2°, m. e. 3.4°± 2.5°). Our novel correction algorithm for pelvic tilt reduced the mean error in anteversion measurements to 0.6°± 0.2°and in inclination measurements to 0.7°(SD± 0.2). Similarly, the mean error due to pelvic rotation was reduced to 0.4°± 0.4°for anteversion and to 1.3°± 0.8 for inclination.

A Novel Method for Correcting Pelvic Tilt on Anteroposterior Pelvic Radiographs

“…They concluded that the measurement of the vertical distance between the pubic symphysis and the sacrococcygeal joint was the most accurate estimator; however, we noted that the sacrococcygeal joint was visible in only a small proportion of cases, making this method difficult to apply broadly. Additionally, other proposed methods of estimating tilt require additional input or measurement, such as lateral views [20] or additional data on the angle of the central beam of the X-ray [27], information that may be difficult to obtain and/or is beyond the current standard of care. In our study, we chose landmarks that are much more likely to be visible on standard AP radiographs, i.e.…”

3D Simulation of Radiographic Projections to Test and Reduce the Effect of Pelvic Tilt on the Accuracy of Cross-table Lateral Radiography

“…To reduce this effect, we derived a correction formula, which can convert the measured values under different PTs into the actual VA values under the natural pelvis, and it was veri ed to be reliable after comparison with the CT values. Several methods have been described for correcting the error of VA measurementowing to the PT in previous studies [15,21,22]. Some of them used formulae as we did [15,21], while othersmodi edmethods using special techniques, such as normograms [22].However, these methods are relatively complex and cumbersome.…”

“…Several methods have been described for correcting the error of VA measurementowing to the PT in previous studies [15,21,22]. Some of them used formulae as we did [15,21], while othersmodi edmethods using special techniques, such as normograms [22].However, these methods are relatively complex and cumbersome. In contrast, our method can achieve reliable correction only through a simple equation.…”

Three-dimensional acetabular orientation during periacetabular osteotomy: a video analysis of acetabular rim position using an external fixator as navigation tool during reorientation procedure

“…Whereas Liu et al considered three-motion components in the sagittal, coronal, and transversal plane, Pflugi et al measured acetabular orientation by means of its anteversion and inclination. Assessment of acetabular orientation by means of anteversion and inclination is well known from total hip arthroplasty [22][23][24]. Description of spatial orientation of a 3D object (acetabular cup) using 2 parameters only (anteversion and inclination) is just possible if the object has an axis of symmetry.…”