Abstract
Introduction: Correct placement of the acetabular cup is a crucial step in total hip replacement to achieve a satisfactory result and remains a challenge with free hand techniques. Imageless navigation may provide a viable alternative to freehand technique and improve placement significantly. The purpose of this study therefore was to assess and validate intra-operative placement values as displayed by the navigation unit to postoperative measurement of cup position using high resolution CT scans.
Methods: 32 patients underwent primary hip joint replacement using imageless navigation. The average age was 66.5 years (range 32–87). 23 non-cemented and 9 cemented acetabular cups were implanted. During surgery we aimed for 45 degrees of inversion and 15 degrees of anteversion. A pelvic CT scan using a multi-slice CT was used to assess the position of the cup radiographically.
Results: 2 patients were excluded because of dislodgement of the tracking pin. Pearson correlation revealed a strong significant correlation (r=0.68; p< 0.006), for cup inclination and a moderate non-significant correlation (r=0.53; p=0.45) between intra-operative readings and cup placement.
Discussion: These findings can be explained with possible introduction of systematic error. Even though the acquisition of anatomic landmarks are simple they must be acquired with great precision. An error of 1 cm can result in a mean anteversion error of 6 degrees and inclination error of 2.5 degrees. Whilst navigation results in highly accurate cup placements in relation to inclination, ante-version of the cup can not be determined accurately.
Correspondence should be addressed to: EFORT Central Office, Technoparkstrasse 1, CH – 8005 Zürich, Switzerland. Tel: +41 44 448 44 00; Email: office@efort.org
Author: Erik Hohmann, Australia
E-mail: ehohmann@optusnet.com.au
