Does An Augmented Reality-based Portable Navigation System Improve the Accuracy of Acetabular Component Orientation During THA? A Randomized Controlled Trial

Abstract

Background: We developed an augmented reality (AR)-based portable navigation system in which the surgeon can view the pelvic plane and placement angle of an acetabular cup on the display of a smartphone during THA.

Questions/purposes: (1) Is acetabular component placement more accurate using the AR-based portable navigation system compared with the conventional freehand technique? (2) Is intraoperative measurement of placement angle more accurate when using the AR-based portable navigation system compared with a goniometer?

Methods: Forty-six patients were randomly assigned to undergo acetabular cup placement during THA using the AR-based portable navigation system (AR navigation group) or placement of a mechanical alignment guide (conventional group). All surgeries were performed with the patient in the lateral decubitus position. We compared the absolute value of the difference between the targeted placement angle and postoperative measured placement angle between the groups using two types of imaging (radiography and CT).

Results: In terms of radiographic inclination, the mean differences between the targeted placement angle and postoperative measured angle were smaller in the AR navigation group than in the conventional group for both radiographs and CT images (2.3° ± 1.4° versus 3.9° ± 2.4°, respectively; p = 0.009 and 1.9° ± 1.3° versus 3.4° ± 2.6°, respectively; p = 0.02). There were no differences in radiographic anteversion between the two groups. No complications were associated with the use of the AR-based portable navigation system.

Conclusions: This system yielded no differences in acetabular anteversion accuracy, and no clinically important differences in acetabular inclination. Therefore, at this time we cannot recommend this device as its costs and risks cannot be justified based on the absence of a clinically meaningful difference in cup placement accuracy. Although we detected no complications, this was a small series, and this approach adds both surgical time and pins in the ilium.

Level of evidence: Level I, therapeutic study.

Fig. 1

This flow diagram illustrates patient enrollment, randomization, and analysis for this study.

Fig. 2

The anterior pelvic plane (APP) and functional pelvic plane (FPP) coordinates were acquired with the patient in the supine position. A guide marker with two 2-mm pins was placed at the iliac crest. The pelvis markers were placed at the right and left anterior iliac spine and pubic symphysis. The AR system acquired APP and FPP coordinates by recognizing the pelvis marker, and it copied their information to the guide marker (blue arrow). The APP and FPP were superimposed on the surgical field on the display of a smartphone.

Fig. 3

A-B (A) Each vector of the APP and (B) FPP and the gravitational vector are shown here. The vector is the direction vector from R (right anterior superior iliac spine) to L (left anterior superior iliac spine). The vector is the direction vector from R to P (pubic symphysis). The vector is the gravitational vector. The vector is defined as the normal vector of APP and is calculated with the cross product of and . The vector is defined as the cross product of and and it is perpendicular to both and . The vector is defined as the normal vector of FPP and is calculated with the cross product of and .

Fig. 4

The AR-based portable navigation system during THA (left hip in the lateral decubitus position) is shown. The assistant held the smartphone, which recognized the handle and pelvis markers. The surgeon placed the acetabular cup according to the AR-based portable navigation system.

Fig. 5

(A) Each vector of the FPP and the cup handle and (B) the top-down view of the FPP. The vector is the direction vector of the cup handle. The angle of radiographic anteversion is calculated with the inner product of and . The angle of radiographic inclination is calculated with the cross product of and and the inner product of and this cross product.

Fig. 6

This is a screenshot of the image in Fig. 4. The surgeon can see the placement angle of the acetabular cup, images of the FPP, and direction of gravity on the smartphone display in real time. The black arrow indicates the FPP image. The white arrow indicates the direction of gravity, which enabled the surgeon to determine the pelvic tilt or rotation.

Fig. 7

The conventional technique during THA (left hip in the lateral decubitus position) is shown. We used an alignment rod designed for 40° radiographic inclination and 15° or 20° radiographic anteversion.

Fig. 8

Measurement of acetabular component angles using a goniometer during THA (left hip in the lateral decubitus position) is shown. The assistant held the goniometer and measured the angle of the cup introducer.