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

Where Are We Now?

Definitions are fundamental to clear communication, and augmented reality is defined as “digitally superimposing virtual objects onto physical objects in real space so individuals can interact with both at the same time” [1]. Augmented reality involves unique hardware and software that allows the surgeon to have a real-time computer-generated image overlaying real life objects displayed onto a computer, tablet, headset, or in the case of the current study, a smartphone. The essential components in surgical augmented reality include tracking, display, and software systems [9].

Augmented reality has the potential to shorten surgical time, reduce radiation exposure, and improve accuracy in fracture care, while also making complex open and arthroscopic surgery more intuitive [4]. I note that we should consider augmented reality more broadly under the larger umbrella of computer-assisted surgery (CAS). Broadly classified into three systems, passive, active and semi-active, CAS is based on the degree of assistance provided [3]. Active and semi-active systems involve robots to either autonomously (active) or haptically (semi-active) perform the surgical steps. Most of the studies on CAS in hip arthroplasty pertain to passive navigation systems, which provide the surgeon preoperative planning and/or live information regarding the implant position but does not actively prepare or place the implant. Navigation systems can be further sub-categorized as either imageless, CT-based, or fluoroscopy-based; in my observation, CT-based systems are the most-frequently reported on navigation technique. The theoretical benefit of augmented reality navigation in the current study is having the familiarity and accuracy of a CT-based navigation system in a portable, potentially low-cost system that utilizes a smartphone.

I found only one clinical study on augmented reality in acetabular component alignment [10], a pilot study from 2018, which found that the use of AR provided greater radiographic accuracy in mean anteversion compared to a goniometer (2.7° versus 6.8°) but no difference in the mean inclination measurement (2.1° versus 2.6°). The theoretical benefits of tighter limits on component positioning include fewer dislocations and greater survivorship; however, with such small observed differences and so many questions about whether any “safe” zone in THA really is all that safe, we should not assume that the theoretical benefits will materialize.

In the current study of one augmented reality system, Ogawa and colleagues [11] performed a randomized trial in 41 patients comparing the accuracy of acetabular component placement using either a portable augmented reality system (augmented reality navigation group) or a mechanical alignment guide (conventional group) in THA. The authors did not identify any radiographic- or CT-measured differences in the acetabular anteversion accuracy or any clinically important differences in acetabular inclination. Specifically, the mean differences between targeted and post-operative acetabular inclination measurements were smaller in the augmented reality navigation group compared to the conventional group (2.3° versus 3.9° for radiographic measurement and 1.9° versus 3.4° for CT measurement) [11]. The lack of substantial improvements in component placement does not support widespread adoption of augmented reality navigation in routine arthroplasty at this time

Where Do We Need To Go?

Perhaps most importantly, we need to determine whether the incremental improvements in alignment that may be possible when computer navigation (and by extension, virtual or augmented reality systems) will reduce the risk of dislocations, bearing-surface wear, or any other endpoint that a patient might perceive; the available evidence, as yet, is unconvincing on those points [2, 8, 12].

Another niche that augmented reality may help to fill is that of education and training. Augmented reality may improve the learner’s psychomotor skill acquisition and ability to conceptualize what is typically invisible, in an environment that poses no risk to patients [6]. One study found that augmented reality helped medical students place acetabular components as accurately as they did when receiving hands-on instruction from an expert, leading the authors to conclude that augmented reality can assist skill acquisition without direct supervision [7].

An unmet clinical need that navigation (and by extension, perhaps augmented reality) might address is the dynamic or virtual assessment spinopelvic mobility and its implications on component placement. The goal, of course, would be to improve impingement-free motion and reduce the risk of dislocation in patients with abnormal spinopelvic mobility. Understanding the shortcomings of the Lewinnek safe zone acetabular has led to an updated concept of “functional stability”; and navigation (with or without augmented reality) may help us achieve it [5], but as of now, this is speculative.

Finally, we need to see how augmented reality as a navigation tool compares to other computer navigation or robotic systems. In particular, we need preclinical and clinical studies to determine whether this technology adds value in THA.

How Do We Get There?

From the education and training perspective, learning curve studies should assess whether augmented reality reduces the time to achieve steady state with surgical time, cost, complications and patient-reported outcomes. Regarding comparing augmented reality to current navigation techniques, testing must go beyond accuracy measurements and needs to include complications (such as dislocations), operative time, and start up and disposable costs. Any putative benefits of augmented reality must be tested before it is deployed. Studies with various tracking, display, and software systems are needed to identify ideal applications and system configurations of the three critical components. Comparison testing should assess the utility of augmented reality to current techniques and systems. Any studies on this must go beyond accuracy measurements, and must include complications (such as dislocation), operative time, and start up and disposable costs. Rather than run away from such a daunting challenge, surgeons and specialty societies should follow the lead of Ogawa and colleagues [11], and partner with other researchers, clinicians, and companies to answer these questions for the benefit of our patients and society.