Introduction In lateral decubitus controlling the pelvic sagittal plane is critical in reducing outliers in radiographic inclination (RI). We have shown that Reality Based Navigation (RBN1) can consistently achieve an apparent operative inclination 35°±2.5°2. However, the range of RI in that paper was 23.4–53.9°. The aim of this study was to determine if the number of RI outliers could be reduced by using RBN in combination with the Belfast Sagittal Plane Positioner. Method As a service evaluation we measured RI in 180 THAs. RBN was used in every case but in group 1 (n=90) we used the Belfast Sagittal Plane Positioner (BSPP) as compared to a standard patient prop in group 2 (n=90). To account for the trigonometric impact of anteversion the chosen target for RI was (35+3) 38°±2.5°. Results All 180 patients achieved a target apparent operative inclination of 35o±2.5o. The RI range in group 1 was 30°–49.6° compared to 28.8°–57.2° in group 2. In group 1; 74.4% n=67 were 38 o±5o compared to 52.2% n=47 in group 2 (p=0.002). In group 1; 94.6% n=85 were within ±10° compared 83.3% n=15 in group 2 (p=0.031). All of these were values >48 o none <28°. Conclusion RBN1 uses inexpensive, reusable instruments. In this series using RBN in combination with the Belfast Sagittal Plane positioner further decreased the variation in RI. These results compare favourably with navigated or robotically assisted THA performed in lateral decubitus.
Beverland et al. (Thu,) studied this question.