84. PRELIMINARY EXPERIENCE WITH THE EOS SYSTEM FOR EVALUATING PATIENTS WITH HIP PROSTHESES

Abstract

Purpose of the study: The analysis of hip prostheses often remains limited to standard x-rays taken in the upright position or a CT scan taken in the supine position. The EOS^® system enables imaging the entire body for head to foot in a lateral and anteroposterior views, in an upright or sitting position. The purpose of this work was to compare the standard radiographic work-up with the EOS system for the analysis of postural elements in patients with hip arthroplasty.

Material and method: This prospective study included 50 patients free of complications. The standard radiographic work-up included AP and lateral views in the upright and sitting positions. The standard then EOS imaging protocols were performed in two different locations. Images were acquired with the patients in a comfortable position: for the sitting position, the knees were flexed 90°. Two operators took measurements to be able to analyse reproducibility of the morphological parameters (incidence, sacroacetabular angle, and the positional parameters (version, sacral slope, Lewinnek angle, sagittal and frontal cup inclinations, pelvifemoral angle and orientation of the prosthetic neck on the lateral standing then AP sitting position). Pelvic rotation was determined on the AP view by comparative measurement of the projected width of the iliac wings in each pelvis. Hip extension reserve was calculated on the hyperextension lateral view.

Results: Reproducibility of position was excellent for different times and locations. Twelve hip (24%) presented significant reproducible rotation in the AP view; for eight of these hips (16%), the phenomenon disappeared in the sitting position. Four hips (8%) had pelvic rotation in the sitting position on the AP view. On the AP pelvic view in the sitting position, three patients had a femoral neck in functional retroversion while the anatomic femoral anteversion was normal on the scanner. The pelvic parameters were equivalent to those already described. The reproducibility of the measures was excellent between the standard x-rays and the EOS images with the exception of measurements involving the centre of the femoral head (incidence, pelvifemoral angle). It was easier to align the femoral axis on the EOS lateral images, particularly for additional calculation of extension reserve. The Lewinnek angle could not be measured in the sitting position in 32 hips (60%) because of insufficient resolution.

Conclusion: The overall evaluation of the pelvis and the subpelvic sector provides new information concerning the respective positions of the cup and the femur in functional situations.