THE USE OF INCLINOMETERS AND REALITY-BASED NAVIGATION FOR ACCURATE ACETABULAR COMPONENT POSITIONING: A RETROSPECTIVE CASE CONTROL STUDY

Accurate positioning of acetabular components in total hip arthroplasty (THA) is linked with good outcomes. Previously, methods used to achieve correct orientation including anatomical landmarks (transverse acetabular ligament), mechanical alignment guides, inclinometers, navigation and robots have been shown to improve positioning to varying degrees. The purpose of this study was to evaluate whether the use of a “Reality-based Navigation” (RBN) recently introduced by Depuy Synthes TM is effective in 1) improving accuracy of placement 2) reducing the number of outliers. From patients who underwent primary total hip arthroplasty in a tertiary referral centre three groups designated by the method used to determine acetabular component orientation were identified: 1) combination of anatomical landmarks and mechanical alignment guides (MAG) 2) inclinometer 3) reality-based navigation (RBN, Depuy Synthes TM ). Two reviewers independently assessed the post-operative radiographs obtained for each patient to measure the inclination and version of the acetabular component using TraumaCad TM software. The angles utilised as standard were safe zones (40 o +/- 10 o for inclination and 15 o +/- 10 o for version). In the first cohort (MAG), the average inclination angle was 39.98 o (SD 4.68) and the average version angle was 17.21 o (SD 6.79). The second cohort (inclinometer) had an average acetabular inclination of 45.21 o (SD= 5.11) and an average version of 22 o (SD 7.12). Finally, the third cohort (RBN) had an inclination angle of 42 o (SD= 5.78) and a version angle of 19.2 o (SD 8.05). The average values for all cohorts were within safe zones. Dislocation rate was 1–2 cases per sample (total = 4). This study showed no significant difference in accuracy or precision between the three different methods used to aid acetabular component positioning. Conventional methods (a combination of anatomical landmarks and mechanical alignment guides) were as effective as inclinometers and reality-based navigation in aiding accurate acetabular cup positioning. MAG and reality-based navigation had lower numbers of outliers for inclination and MAG outliers were lowest for version.