Computer navigation of the acetabular component

Abstract

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 degrees ) than for inclination (sd 6.3 degrees ). 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.

Six Sigma Analysis of Minimally Invasive Acetabular Arthroplasty: A Preliminary Investigation

“…For example, subtle differences for ASIS referencing would not alter anteversion considerably as long as these points remained in the APP. Spencer et al [35], however, reported higher variation for anteversion than for inclination, and substantial interobserver variability.…”

“…Only one cadaver was used. However, published studies and our prior study used only limited numbers of cadaver specimens [17,29,35,38,40]. In clinical practice, there undoubtedly would be more variability for imageless referencing if more specimens would have been used.…”

“…In our example, we chose 10°above and below the reference position based on the historical comparison of Lewinnek et al [25]. To analyze the comparative ability of the Six Sigma ratio, we evaluated other similar computer navigation acetabular studies that adequately reported descriptive statistics [9,17,29,35,37,40] ( Table 3). CT for navigation referencing provided satisfactory precision, whereas fluoroscopy was capable in some studies but not in others.…”

“…We believe the reference points of the ASISs are relatively broad surfaces and considerable error may be added by touch-point referencing [36,38]. Although some studies suggest this error is tolerable, Spencer et al [35] reported substantial variation using this approach [38]. From our prior work, we predicted the error with imageless referencing would be greater for inclination because this measurement is made in the coronal plane, which is colinear with the APP.…”

“…For computer navigation, the APP was determined. Recent studies have advanced the use of this structure because of the definable landmarks presented [19,26,29,35,37,43]. For purposes of this investigation, the APP was defined as the plane defined by the most anteriorly prominent aspect of the two ASISs and the most prominent anterior portion of the symphysis pubis.…”