Computer Navigation in Shoulder Arthroplasty

The Importance of Accurate Component Placement

In shoulder arthroplasty, accurate placement of the components is universally agreed to be critical for a successful outcome. Multiple studies have demonstrated that deviations in glenoid inclination contribute to post-operative instability after reverse total shoulder arthroplasty while deviations in glenoid inclination and version contribute to loosening after anatomic total shoulder arthroplasty, and lack of component seating contributes to loosening after anatomic total shoulder arthroplasty (4,3). However, when performing shoulder arthroplasty, it can be a struggle for the surgeon to assess these factors. The glenoid is one of the most difficult aspects of the shoulder to expose and version and inclination are measured relative to the body of the scapula, which the surgeon cannot see during surgery. So, it’s no surprise the article by y by Schoch, et al. showed that even expert shoulder surgeons often fail to accurately place glenoid components (2).

Pre-Operative Planning Software: A Step Forward

Multiple companies have released pre-operative planning software that allows the surgeon to view a three-dimensional reconstruction of the scapula and to measure the version and inclination of the glenoid. The surgeon can then virtually “implant” components, and measure their version, inclination, seating, and test the achieved range of motion in the virtual joint. While this motion may not directly correlate with patient range of motion, it allows the surgeon to visualize potential sources of osseous impingement that may lead to changing the position of the components or removing the impinging bone intra-operatively. While this software is great, once the plan is made, it is still up to the surgeon to attempt to replicate the plan intra-operatively. This remains a challenge, with at least one study showing that even in expert hands, deviations from the plan of >10° in version and inclination can occur (2). So planning, while helpful, may not be enough to consistently achieve accurate component placement.

Bridging the Gap Between Planning and Execution

There are several options available to help bridge the gap between pre-operative planning and intra-operative execution such as patient-specific instrumentation and custom glenoid implants. However, these incur significant expenses, require a delay for manufacturing, can still result in inaccurate component placement if the instruments do not fit well, and PSI still only guides version and inclination without determining implant seating, while custom implants are even more costly, have variability in the ingrowth provided and, in my experience, have the added challenge of requiring a perfect fit or they will have even less bone-implant contact than traditional components with eccentric reaming.

The Role of Intra-Operative Navigation

The best solution to allow the surgeon to execute their pre-operative plan would be inexpensive, rapidly deployable, quick, and would allow the surgeon to replicate not just the planned version and inclination of the component, but also the seating. This is why I believe intra-operative navigation, such as ExactechGPS, is the technology that currently best meets these needs. Once a CT is obtained, it allows the surgeon to plan immediately prior to surgery with no lead time, is much less expensive than both PSI or custom-made implants, adds only 3 additional minutes of operative time, in my experience, and allows the surgeon to replicate the pre-operatively planned version and inclination within +/- 2 degrees (6). It also allows the surgeon to confirm that their planned version and inclination was achieved and confirms final component placement. It shows the surgeon their planned reaming depth and allows live screw guidance in reverse total shoulder arthroplasty, optimizing screw length and trajectory (5).

Evidence Supporting Navigation in Shoulder Arthroplasty

Cheung and Ramakrishnan’s review article nicely highlights these aspects but also reviews a large portion of the literature on navigation to date. The reviewed literature is conclusive in showing that navigation allows the surgeon to replicate their plan (6), that it is safe (1), and that it has a short learning curve (7). While long-term follow up is still needed, the promise of this technology to reduce complications in shoulder arthroplasty in the short term is clear. A study by Youderian, et al. comparing navigated and non-navigated cohorts demonstrated a 50% reduction in complication and revision rates for both anatomic and reverse shoulder arthroplasty (1).

Conclusion: Why Navigation Matters

Our obligation as surgeons is always to do our best to improve the lives of our patients, and to make use of whatever tools are at our disposal to achieve this goal. Navigation is just such a tool to improve the accuracy of component position and seating in shoulder arthroplasty.