A novel mechanical inclinometer device to measure acetabular cup inclination in total hip arthroplasty

Abstract

It is well recognised that acetabular cup orientation influences patient function and implant survival post-THR. Reliable intra-operative determination of cup orientation remains a challenge. We describe the design and testing of a novel mechanical inclinometer to measure intra-operative acetabular cup inclination. The aim was to design a generic inclinometer to measure acetabular inclination to within + 5° without requiring modification to existing instrumentation while remaining easy to handle, robust/reusable, and sterilizable. The device was drafted using CAD software, prototyped using a 3D printer and constructed using stainless steel. Two experiments were undertaken to test accuracy: (1) the absolute accuracy was tested; (2) placement of an acetabular component using the device was compared to a freehand technique using a sawbone pelvis. 18 surgeons were asked to place an uncemented acetabular cup in a saw bone pelvis to a target of 40°. The average root-mean-square error was 1.1° (SD: 0.9°). Comparison showed that with the freehand component placement 50% of the surgeons were outside the specified range (35°–45°) where all participants achieved placement within range when using the inclinometer. This work demonstrates that the design and initial testing of a mechanical inclinometer which is suitable for use in determining the acetabular cup inclination in THR.

Keywords:

• Acetabular component inclination
• total hip replacement
• THR
• inclinometer

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. Professor Pandit is a National Institute for Health Research (NIHR) Senior Investigator. Mr van Duren is a BRC-NIHR Academic Clinical Lecturer. The views expressed in this article are those of the author(s) and not necessarily those of the BRC, NIHR, or the Department of Health and Social Care.