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. 2025 Jun 25;7(1):36.
doi: 10.1186/s42836-025-00312-3.

Component orientation measurements in total hip arthroplasty using an inertial measurement unit-based smart trial system

Hao Tang  1 , Yixin Zhou  2 , Baojun Mai  3 , Binjie Zhu  3 , Ping Chen  3 , Yujia Fu  3 , Guangzhi Wang  4
Affiliations

Component orientation measurements in total hip arthroplasty using an inertial measurement unit-based smart trial system

Hao Tang et al. Arthroplasty. .

Abstract

Background: Intraoperative measurement of component orientation represents a basis for optimizing outcomes after total hip arthroplasty (THA). Although the use of computer navigation systems in THA has improved the accuracy of component positioning, they have not gained widespread popularity due to their complexity, time demands, and time-consuming protocols.

Methods: We developed an Inertial Measurement Unit-based Hip Smart Trial system (IMUHST) to assist with intra-operative monitoring of hip posture. An in vitro validation experiment was conducted using a sawbones with a three-dimensional (3D) measurement model as the reference standard.

Results: The absolute mean error, Bland-Altman analysis, and Intra-class Correlation Coefficient revealed that the accuracy and precision of this system meet the threshold for clinical application.

Conclusions: In conclusion, this in vitro validation demonstrates that the IMUHST system provides accurate component orientation measurements while eliminating the cost and complexity of optical navigation, offering a practical solution for widespread adoption. Video Abstract.

Keywords: Anteversion; Computer-assisted surgery; Inclination; Inertial measurement unit; Smart trial system; Total hip arthroplasty.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: Ethical approval is not required in this study. Consent for publication: All presentations provided consent for publication. Competing interests: Yixin Zhou is the Editorial Board Member of Arthroplasty, and other authors declare that they have no competing interests. All authors were not involved in the journal’s review or decisions related to this manuscript.

Figures

Fig. 1
Fig. 1
The inertial measurement unit-based hip smart trial system (IMUHST) is composed of a hollow trial head containing IMU sensors mounted onto a trial stem and reduced into the acetabular cup for assessment
Fig. 2
Fig. 2
Experimental setting and measurement protocol of the robotic system and IMUHST. A The cup is inserted and assessed by the MAKO robotic system as the reference method, and the neutral position of the stem is recorded by the IMUHST to measure the vertical angle between this position and the gravity axis to calculate stem version (SV); B The stem neck is then rotated into a position perpendicular to the cup opening plane, guaranteed by a circular plastic mold. The angle between the initial neutral position and the current position is measured as the radiographic anteversion (RA), and the angle between the current stem neck axis and the horizontal plane is measured for calculation of radiographic inclination (RI); C The neutral position of the femur is guaranteed by a gradient put on a metal pin passing the trans-epicondyle axis. D The stem version can be adjusted for 5° increments between − 50° and 80°, and measured using the robotic system as a reference
Fig. 3
Fig. 3
A schematic drawing of the algorithm for radiographic anteversion (RA), radiographic inclination (RI), and stem version (SV) calculations. The femur is first held at a neutral position, with SV measured as the difference between the axial projection of the neck and vertical line; the femur was then flexed and internally rotated to measure RA. RA = f (α − SV)
Fig. 4
Fig. 4
The Bland–Altman analysis of the measured results of the two systems in (A). cup radiographic anteversion (RA); B cup radiographic inclination (RI); and C. stem version (SV) with anteversion marked positive. IMUHST = Inertial Measurement Unit-based Hip Smart Trial system
See this image and copyright information in PMC

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