Related Experiment Video
Updated: May 16, 2025
Individualized Stem-positioning in Calcar-guided Short-stem Total Hip Arthroplasty
Published on: February 27, 2018
Reducing variability in apparent operative inclination (AOI) during total hip arthroplasty: comparing the ball in
Christopher W Goodland1, Andrew Crone1, Mark Robinson1
1Primary Joint Unit, Musgrave Park Hospital, Belfast, UK.
Introduction:
When operating in lateral decubitus apparent operative inclination (AOI) is the angle between the handle of the acetabular cup introducer and the theatre floor. A digital inclinometer has demonstrated optimal control of AOI. This study aims to compare the deviation from a target AOI with a novel autoclavable ball-in-cage mechanical alignment guide (MAG) as compared to a digital inclinometer.
Methods:
90 primary total hip arthroplasty cases performed in lateral decubitus using a posterior approach were included. The ball-in-cage mechanical alignment guide on a standard Pinnacle cup introducer handle was used to achieve the target AOI of 35° ± 2.5°. Final AOI was measured with a digital inclinometer. These readings were compared to a published historical series of 90 patients using a digital inclinometer.
Results:
The ball-in-cage MAG mean inclination was 35.0° (range 32.5-37.4°), with 100% falling within target. This compared to a mean inclination of 34.0° (range 27.5-37.5°), with the digital inclinometer where 87.8% fell within target. However, the range of postoperative radiographic inclination for the ball-in-cage MAG was 23.4-53.9° with 31.1% being outside a ±5° target.
Conclusions:
These results indicate that this simple autoclavable ball-in-cage MAG consistently achieves an intraoperative AOI within target range. In isolation this does not guarantee a postoperative radiographic inclination within target range.
