Glenoid positioning technology in total shoulder arthroplasty comes with pros and cons

The volume of total shoulder arthroplasty has increased substantially over the past several decades. As the operation continues to modernize, the utilization of navigation continues to expand. Although its theoretical advantage is clear, its clinical benefit, cost, and ease of incorporation remain debated.

Preoperative planning technology
Over the years, shoulder arthroplasty longevity has improved dramatically with the advancements of modern materials and techniques. The importance of appropriate implant positioning has been emphasized in modern literature, as this is one of the main factors that is in the surgeon’s control. Many studies have established a connection between implant malposition and early failure with poor postoperative outcomes. Traditional aiming guides have been used to establish implant version and inclination intraoperatively and to keep positioning within an acceptable anatomic range. In patients with significant deformity or preexisting bone loss, the use of traditional guides and reference points may be challenging and inaccurate. Several technological advancements have been developed to help plan and position arthroplasty components in the appropriate position.

Preoperative surgical templating has significantly changed surgical planning. A preoperative CT scan is typically used with planning software to evaluate the patient’s bony anatomy; it can create a 3D model, predict implant size, and guide appropriate positioning. This software can assist surgeons in visualizing implant position, predicting distalization and lateralization, and calculating reaming depth before they step foot in the OR. This allows a smoother flow of surgery, as the surgeon can anticipate and address problems with implant sizing or positioning preoperatively. Execution of the plan remains difficult, however, as even the most experienced surgeons have a 10-degree range of error from their preoperative plan using freehand techniques. This range is increased in cases with significant deformity and bone loss.

Patient-specific guides have been created to help surgeons better execute their plans intraoperatively. Several companies have developed custom guides that are constructed based on preoperative CT scanning to improve consistency of implant positioning. The guides, however, are not perfect, as they carry an increased cost and a risk of surgical delay due to manufacturing time. The guides are also created using the patient’s native anatomy, which often includes osteophytes. Removal of such osteophytes is often a part of appropriate exposure, which therefore alters the bony architecture, diminishing the utility of guides. As a potential solution, some companies have developed reusable guides that can be adjusted based on preoperative CT. Reusable guides address the added cost component and can expedite time to surgery. However, planning still relies on maintaining osteophytes that may interfere with adequate exposure and may not fit the patient’s morphology as well as a truly custom guide.

Computer- and robotic-assisted tools
Several orthopaedic technology companies have developed computer-assisted intraoperative navigation systems that are comparable to those used in total knee and hip arthroplasty. These systems use the preoperative CT scan, combined with intraoperative infrared guides, to allow the surgeon to visualize complete bony morphology and component positioning in real time. In these systems, the surgeon performs the operation with standard instrumentation and attached sensors.

Several options exist for the display of this information. One option includes a separate display screen in the OR, which requires sterile draping and pulls the surgeon’s attention from the operative field. Another includes virtual reality goggles/glasses that the surgeon wears to project information onto the surgical field; although futuristic, these glasses have been described as cumbersome to wear and disorienting during initial usage.

Although the added cost with the use of these systems is relatively negligible, as both are available for multiple uses and do not require purchase by facility, there is a concern for added time intraoperatively to incorporate such systems into the regular OR workflow. Dependence on such technologies has also been discouraged due to the risk of malfunction during surgery.

Similar to its recent adoption in total knee and hip arthroplasty, robotic-assisted total shoulder arthroplasty is now an option for surgeons. Robotic-assisted surgery involves docking a robotic arm that is either directly controlled by the surgeon or is used to guide the surgeon’s instruments and implant positioning. Due to their size, such robots are often expensive and remain in the hospital long term. In smaller ORs, the robots may also take up valuable workspace and potentially compromise sterility.

Occasionally, a robot purchase or rental agreement by the hospital forces surgeons to use implants from the same manufacturer, regardless of each surgeon’s individual preference and comfort level.

Other innovations are created on an almost monthly basis that may assist surgeons in obtaining improved intraoperative component positioning. These innovations are particularly useful for surgeons who are newer to practice and may still lack extensive experience with glenoid instrumentation.

Proper implant positioning is important, and various navigation systems have been shown to improve intraoperative component placement; however, there is a lack of high-level literature demonstrating improved patient-reported outcomes with the utility of such technologies.

As our healthcare system transforms to a more cost-aware model, critical evaluation of those technologies is required to determine their true cost-to-benefit ratio.

Marc Schatz, MD, is an orthopaedic sports medicine/shoulder and elbow fellow at University of Tennessee–Campbell Clinic.

Thomas (Quin) Throckmorton, MD, FAAOS, is professor of shoulder and elbow surgery and vice chief of staff at the University of Tennessee–Campbell Clinic Department of Orthopaedic Surgery.