23.1 Introduction

As we have developed much better understanding of the biomechanics of reverse shoulder arthroplasty (RSA), we have come to the realization that proper implant positioning and fixation is critically important. In addition to this obvious consideration, there are now increasing indications for RSA in patients with even more glenoid bone deformities.

Improvements in imaging technology have given rise to a number of different types of patient-specific guide systems to improve glenosphere baseplate positioning. The debate in this chapter is not whether this technology is useful in complex situations, but whether it is imperative in all cases.

23.2 Patient-Specific Instrumentation: It Should Be Used Routinely!

Unlike anatomic shoulder arthroplasty, RSA is often used as a last resort. Bearing this in mind, shoulder surgeons should strive to implant the prosthesis in as perfect a position as possible. Accurate baseplate and glenosphere placement in the scapula can be technically challenging, and in cases of severe bone loss, it can be even more difficult. Improper glenosphere positioning can lead to significant complications including notching, loosening, and instability.1 To achieve optimal outcomes for patients and improve implant longevity, all measures that can potentially minimize these complications should be taken. Computerized planning and patient-specific instrumentation (PSI) are two of the most viable ways to improve implant positioning.

Planning software and PSI have been successfully used for years in both total hip and total knee arthroplasties. Most studies have shown improved implant positioning with computerized planning. Similar results have been reported for RSA. Venne et al demonstrated improved precision of both baseplate and screw placement in a cadaver model.2 Stubing et al published similar findings in cadaver models. Using three-dimensional (3D) navigation, glenoid baseplate positioning was improved, with a mean deviation of 1.6 degrees compared to 11.5 degrees using nonnavigated techniques.3

PSI for both anatomic total shoulder replacement (TSR) and RSA has produced similar results in cadaver studies.4,5 Walch et al exhibited excellent correlation between central guide preoperative planning and actual central guide pin placement.4 Throckmorton’s group had shoulder surgeons place glenoid components in cadaver scapulae with and without the use of PSI.5 Throckmorton et al also conducted a study on central pin positioning for RSA; they did not find a difference between using PSI and standard techniques.5 One issue, highlighted by the work of Hendel et al, is that the greatest benefit is often seen in patients with more severe glenoid deformities.6 Levy et al used PSI in cadavers to implant RSA glenospheres and found that using it correlated well with the preoperative plan.7 Clearly cadaver studies help justify what we do as orthopedic surgeons, but the results do not always translate clinically.

Given the relatively short time period that PSI has been used for RSA, few clinical studies assessing its effect on outcomes exist. Studies such as the one conducted by Gerber et al have shown an association between outcomes and malposition/superior tilt of glenoid components.8 Based on these reports, Heylen et al hypothesized that using planning software and PSI would result in decreased variability in glenoid component inclination (in both anatomic TSR and RSA).9 Their study included 36 patients, 9 of whom had severe glenoid deformities, and found that the use of planning software and PSI supported their initial hypothesis. Furthermore, it avoided extreme inclination errors, which would cause early failure.

Initially a drawback to using planning software and PSI was its limited availability. Only a few companies had such products, which meant that if a surgeon wanted to use it, they may have been forced to use an implant with which they were not familiar. Given the theoretical benefits of such technology, at this point, most companies that make shoulder arthroplasty implants have their own version of planning software and PSI. As these products are more widely available, more clinical studies and longer-term follow-up data will be available, likely supporting their use.

Most shoulder specialists would agree that there is undeniable benefit to this technology in cases of significant glenoid bone loss. That said, there is probably significant benefit for surgeons who do not perform a tremendous of amount of shoulder arthroplasties even if there is no significantly altered anatomy.

The cost-benefit analyses still need to be done, but if the added cost leads to improved implant positioning which decreases the complication rate, I would submit that the added cost is worth it. And if improved positioning, even if only by a few degrees, leads to even an incremental gain in implant survivorship, it would be worthwhile.