Toward a Dynamic Approach of THA Planning Based on Ultrasound

Abstract

The risk of dislocation after THA reportedly is minimized if the acetabular implant is oriented at 45°i nclination and 15°anteversion with respect to the anterior pelvic plane. This reference plane now is used in computerassisted protocols. However, this static approach may lead to postoperative instability because the dynamic variations of the pelvis influence effective cup orientation and are not taken into account in this approach. We propose an ultrasound tool to register the preoperative dynamics of the pelvis for THA planning during computer-assisted surgery. To assess this pelvic behavior and its consequences on implant orientation, we tested a new 2.5-dimensional ultrasound-based approach. The pelvic flexion was registered in sitting, standing, and supine positions in 20 subjects. The mean values were -25.2°± 5.8°(standard deviation), 2.4°± 5.1°, and 6.8°± 3.5°, respectively. The mean functional anteversion varied by 26°and the mean functional inclination by 12°depending on the pelvic flexion. We therefore recommend including dynamic pelvic behavior to minimize dislocation risk. The notion of a safe zone should be revisited and extended to include changes with activity.

The Effects of Body Position on Pelvic Tilt Angles Measured with a Smartphone-Based Navigated Ultrasound System in Symptom-Free Young Adults

“…If cup alignment is only based on PT angles measured in the supine position, significant PT differences between the supine and upright positions may affect the stability of the hip negatively and lead to dislocations. Therefore, Dardenne et al [21] recommended that the notion of a "safe zone" should be revised to minimize the dislocation risk. PT changes with activity should be considered.…”

Intra‐ and Inter‐rater Reliability of Navigated Ultrasound in the Assessment of Pelvic Tilt in Symptom‐Free Young Adults

“…Pelvic tilt angles can assume posterior and anterior values, and they provide insight into the position of the pelvis in relation to the frontal plane. The question of whether pelvic tilt angles measured with the patient in the supine position are adequate for THA planning was addressed in some studies . In one of the studies, the acetabular components of 16 patients were orientated within the “safe zone” in the supine position but outside the safe zone in the standing position.…”

Ultrasound-based registration of the pelvic coordinate system in the lateral position using symmetry for total hip replacement

“…x 1 most anterior point of the ipsilateral ASIS y 1 most anterior point of the contralateral ASIS x 2 = y 2 fi rst arbitrary point of the symphysis x 3 = y 3 second arbitrary point of the symphysis x 4 = y 4 third arbitrary point of the symphysis x 5 = y 5 most posterior point of S1 (sacral spine) x 6 = y 6 most posterior point of S2 (sacral spine) x 7 = y 7 most posterior point of S3 (sacral spine) x 8 = y 8 most posterior point of L5 (lumbar spine) x 9 = y 9 most posterior point of L4 (lumbar spine) x 10 = y 10 most posterior point of L3 (lumbar spine) For each of these 11 points, the position chosen by the fi rst surgeon and the position chosen by the second one were averaged before further symmetry analysis to reduce the impact of interactive localization errors.…”

“…It has been argued that the patient-specifi c dynamic pelvic orientation in everyday life situations such as standing and sitting might play an important role for the functional outcomes of THR surgery. Whereas approaches based on X-ray imaging [1,8] and ultrasound imaging [6] have been suggested for the pre-operative measurement of the pelvic orientation, the question how to use these data for therapy planning still needs to be clarifi ed. For a summary of the current status of cup positioning in THR and open questions, the reader is referred to the literature (see, e.g., refs.…”