Regardless of the intraoperative goals for placement and orientation of the glenosphere components, it is vitally important to accurately and consistently meet those goals for achieving optimal patient outcomes. Verborgt and colleagues20 implanted 7 glenospheres in cadaveric specimens without any glenohumeral arthritis using standard techniques to evaluate the accuracy of glenosphere version and inclination. Their goal was to place components in neutral version and with 10° of inferior inclination. Their average glenoid version postoperatively was 8.7° of anteversion, and their average inclination was 0.9° of superior inclination. Throckmorton and colleagues21 randomized 35 cadaveric shoulders to receive either an anatomic or a reverse total shoulder prosthesis from high-, mid-, and low-volume surgeons. They found that components placed using traditional guides averaged 6° of deviation in version and 5° of deviation in inclination from their target values, with no significant differences between surgeons of different volumes.
PATIENT-SPECIFIC GUIDES/INSTRUMENTATION
Patient-specific guides/instrumentation and intraoperative navigation are the 2 techniques that have been used to improve the accuracy of glenoid and glenosphere placement. Both techniques require the use of high-resolution CT scans and computer software to determine the proper position for glenoid or glenosphere placement based on the patient’s individual anatomy. Patient-specific guides and instrumentation use the data acquired from a CT scan to generate a preoperative plan for the location and orientation of the glenoid baseplate. Once the surgeon approves the preoperative plan, a patient-specific guide is created using the patient’s glenoid as a reference for the location and orientation of the central guide pin. The location of the central guide pin on the glenoid determines the center of the glenoid baseplate, and the guide pin’s orientation determines the version and inclination of the glenoid or the glenosphere. Once the guide pin is placed in the glenoid, the remainder of the glenoid implantation uses the guide pin as a reference, and, in that way, patient-specific guides control the orientation of the glenoid at the time of surgery.
Intraoperative navigation uses an optical tracking system to determine the location and orientation of the central guide pin. Navigation systems require intraoperative calibration of the optical tracking system before they can track the location of implantation relative to bony landmarks on the patient’s scapula. Their advantage over patient-specific instrumentation (PSI) is that they do not require the manufacture of a custom guide; however, they may add significantly increased cost and surgical time due to the need for calibration prior to use and the cost of the navigation system along with any disposable components associated with it. Kircher and colleagues22 performed a prospective randomized clinical study of navigation-aided TSA compared with conventional TSA and found that operating time was significantly increased for the navigated group with an average operating room time of 169.5 minutes compared to 138 minutes for the conventional group. They also found that navigation had to be abandoned in 37.5% of their navigated patients due to technical errors during glenoid referencing.
COMMERCIAL PATIENT-SPECIFIC INSTRUMENTATION SYSTEMS
The 2 types of PSI that are currently available are single-use PSI and reusable PSI. The single-use PSI involves the fabrication of unique guides based on surgeon-approved preoperative plans generated by computer-software-processed preoperative CT scans. The guides are fabricated to rest on the glenoid articular surface and direct the guide pin to the correct location and in the correct direction to place the glenoid baseplate in the desired position with the desired version and inclination. Most of these systems also provide a 3-D model of the patient’s glenoid so that surgeons can visualize glenoid deformities and the correct guide placement on the glenoid. Single-use PSI systems are available from DJO Global, Wright Medical Group, and Zimmer Biomet. The second category of PSI is reusable and is available from Arthrex. The guide pin for this system is adjusted to fit individual patient anatomy and guide the guide pin into the glenoid in a location and orientation preplanned on the CT-scan-based computer software or using a 3-D model of the patient’s glenoid (Table).
Table. Details of Available Patient-Specific Instrumentation Systems
| System | Manufacturer | Single-Use/Reusable | Guides |
| MatchPoint System | DJO Global | Single-use | Central guide pin |
| Blueprint 3D Planning + PSI | Wright Medical Group | Single-use | Central guide pin |
| Zimmer Patient Specific Instruments Shoulder | Zimmer Biomet | Single-use | Central guide pin, reaming guide, roll guide, screw drill guide |
| Virtual Implant Positioning System | Arthrex | Reusable | Central guide pin |
The DJO Global patient-specific guide is termed as the MatchPoint System. This system creates 3-D renderings of the scapula and allows the surgeon to manipulate the glenoid baseplate on the scapula. The surgeon chooses the glenoid baseplate, location, version, and inclination on the computerized 3-D model. The system then fabricates a guide pin matching the computerized template that references the patient’s glenoid surface with a hook to orient it against the coracoid. A 3-D model of the glenoid is also provided along with the customized guide pin.
Continue to: Blueprint 3D Planning + PSI...