We have evaluated in vitro the accuracy of percutaneous and ultrasound registration as measured in terms of errors in rotation and version relative to the bony anterior pelvic plane in computer-assisted total hip replacement, and analysed the intra- and inter-observer reliability of manual or ultrasound registration. Four clinicians were asked to perform registration of the landmarks of the anterior pelvic plane on two cadavers. Registration was performed under four different conditions of acquisition. Errors in rotation were not significant. Version errors were significant with percutaneous methods (16.2°; p < 0.001 and 19.25° with surgical draping; p < 0.001), but not with the ultrasound acquisition (6.2°, p = 0.13). Intra-observer repeatability was achieved for all the methods. Inter-observer analysis showed acceptable agreement in the sagittal but not in the frontal plane. Ultrasound acquisition of the anterior pelvic plane was more reliable in vitro than the cutaneous digitisation currently used

Our aim was to assess the intra- and inter-observer reliability in the establishment of the anterior pelvic plane used in imageless computer-assisted navigation. From this we determined the subsequent effects on version and inclination of the acetabular component. A cadaver model was developed with a specifically-designed rod which held the component tracker at a fixed orientation to the pelvis, leaving the anterior pelvic plane as the only variable. Eight surgeons determined the anterior pelvic plane by palpating and registering the bony landmarks as reference points. The exact anterior pelvic plane was then established by using anatomically-placed bone screws as reference points. The difference between the surgeons was found to be highly significant (p < 0.001). The variation was significantly larger for anteversion (. sd. 9.6°) than for inclination (. sd. 6.3°). The present method for registering pelvic landmarks shows significant inaccuracy, which highlights the need for improved methods of registration before this technique is considered to be safe

Abstract. Objectives. The importance of cup position on the performance of total hip replacements (THR) has been demonstrated in in vitro hip simulator tests and clinically. However, how cup position changes during gait has not been considered and may affect failure scenarios. The aim of this study was to assess dynamic cup version using gait data. Methods. Pelvic movement data for walking for 39 unilateral THR patients was acquired (Leeds Biomedical Research Centre). Patient's elected walking speed was used to group patients into high- and low-functioning (mean speed, 1.36(SD 0.09)ms. −1. and 0.85(SD 0.08)ms. −1. respectively). A computational algorithm (Python3.7) was developed to calculate cup version during gait cycle. Inputs were pelvic angles and initial cup orientation (assumed to be 45° inclination and 7° version, anterior pelvic plane was parallel to radiological frontal plane). Outputs were cup version angles during a gait cycle (101 measurements/cycle). Minimum, maximum and average cup version during gait cycle were measured for each patient. Two-sample t-test (p=0.05) was used to compare groups. Results. Over a gait cycle the mean minimum, maximum and average version angles for the high-functioning group were −4.5(SD 4.4)°, 5.0(SD 4.3)°, 9.5(SD 4.0)° and for low-functioning group 2.0(SD 3.7)°, 6.2(SD 2.9)°, 8.1(SD 3.2)°. There were no significant differences for the minimum, maximum and average version angles between the two groups. Conclusions. The study shows that dynamic acetabular cup version changes substantially during gait and this must be considered clinically and in pre-clinical testing. There was no significant difference between the two groups; however, dynamic cup version was more negative in high-functioning compared to low-functioning patients. Further studies on a larger cohort are required to determine whether patients’ profiles can be stratified to provide enhanced inputs for pre-clinical THR testing. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

In vitro biomechanical tests allow obtaining important information about stresses and deformations inside the bone, and about the displacements of the prosthetic device under physiological load conditions. This information may be helpful for the development of innovative devices, for the improvement of the existing ones, and for defining optimized procedure for bone reconstruction depending on the typology of bone defects. The definition of a robust and reproducible reference frame is the first step in order to perform a consistent biomechanical test [1]. The aims of the current study was to define an anatomical reference frame for pelvis which can also be applied to a hemi-pelvis. A robust alignment method was sought so as to replicate the anatomical pose during in vitro applications. The intra- and inter- operator repeatability was quantified to corroborate the results. The anatomical reference frame was derived from the anterior pelvic plane [2] and was adapted for in vitro applications. It was based on the following anatomical landmarks: Anterior Superior Iliac Spine (ASIS, defined as the most prominent point on the external iliac surface); Posterior Superior Iliac Spine (PSIS) defined as the upper and most prominent projection on the posterior border of the iliac wing); Pubic Tubercle (PT, defined as the most medial point on the extension of inner line of upper oval foramen). The alignment procedure represented an improved version of a previous procedure [3]. The hemi-pelvis has been positioned on blocks of plasticine close to the landmarks on a 5-screws adjustable plate. Three steps were performed: position of the landmarks at the same height; alignment of the PSIS and PT on a horizontal line parallel to x- direction; position of the setup in front of a 6 degrees of freedom manipulator so that both the manipulator and the 5-screws adjustable plate are in the same reference frame. The manipulator was used to move the specimen in the following steps: clamping and lifting up of the specimen; rotation around x-axis in the posterior direction by 45°; rotation around y-axis in the medial direction by 90°; rotation around x-axis (antero-posterior direction) until PT and ASIS lay in the same vertical plane. Five operators performed the alignment of a male and a female hemi-pelvis, three times each. The repeatability of the current procedure was good, with uncertainties below 1.0° within the same operator, and of less than ±1.5° between operators for the male hemipelvis, and ±2° for the female one. Thanks to the good results the reference frame and the alignment procedure may be adopted for in vitro biomechanical testing on hemi-pelvic specimen, for example to test acetabular bone reconstruction or acetabular prosthetic devices

Objectives

Acetabular component orientation in total hip arthroplasty (THA) influences results. Intra-operatively, the natural arthritic acetabulum is often used as a reference to position the acetabular component. Detailed information regarding its orientation is therefore essential. The aim of this study was to identify the acetabular inclination and anteversion in arthritic hips.