Why Navigation is Critical in Shoulder Arthroplasty

3D imaging technology has led to a much better understanding of glenoid morphology and how it is affected by the wear process in shoulder arthritis. The pathologic triad as decribed by Matsen (1. posterior humeral subluxation; 2. increased glenoid retroversion; 3. biconcave glenoid) is encountered in many arthritic shoulders. Other wear patterns like superior erosion may also commonly occur in certain conditions like cuff tear arthropathy. One of the principle goals of shoulder replacement, whether anatomic or reverse, is to recognize and correct pathologic glenoid deformity as failure to do so may risk premature loosening of the glenoid implant due to abnormal loading mechanics.

Unfortunately, even experienced shoulder surgeons do a poor job in correcting glenoid erosion. A meta-analysis by Sadoghi et al demonstrated an average error in glenoid correction of +/- 11 degrees. Other research by Iannotti et al showed an angular variability of 10 degrees in pin placement using a free-hand technique.

This lack of precision is no longer acceptable given today's technology. Advanced CT imaging has allowed surgeons to preoperatively plan placement of the glenoid component with the goal of correcting pathologic version, minimizing bone loss and preventing penetration of the glenoid vault. As many systems now offer augmented glenoid implants, such systems also allow selection of the optimal implant for each given case. We have performed research looking at the ability or surgeons to recreate a preoperative plan using conventional, free-hand instruments compared to surgical navigation. Our results demonstrate that even with planning, a surgeon's ability to execute that plan remains very inaccurate. The scatter plot above shows the range of implantation variability without navigation in blue compared to with navigation in orange. These results clearly show that eye-balling it in the operating room is no longer acceptable with today's technology.

The GPS (Guided Persronalized Surgery) platform is a surgical navigation system that allows the surgeon to register the patient's anatomy with their CT scan. Trackers attached to the scapula and the instruments then allow the surgeon real-time visualization of glenoid preparation so that the preoperative plan can be replicated with great precision. Navigation can help surgeons place and orient the central cage hole, the reaming of the glenoid surface and the placement of fixation screws in the reverse shoulder. Future developments will include navigation of implant rotation.

Particularly in complex cases with severe retroversion, severe erosion or a very narrow glenoid vault, navigation can ensure optimal placement and fixation of the implant to reduce the risk of complications. Some cases have very little margin for error and given the demands that today's patients place on their implants, it is up to surgeons to maximize outcomes and durability using modern navigation technology. Ten degrees of error is a recipe for premature implant failure.

The picture below shows improved precision that GPS can provide the shoulder arthroplasty surgeon. This is the only system that currently allows real time navigation of a preoperative plan. On April 1st, 2019, the GPS system will be available for consignment so that hospitals do not have to purchase the computer system. This will make the technology widely available to any surgeon in combination with the Equinoxe shoulder system.