Blueprint 3D Planning + PSI (Wright Medical Group) allows custom placement of the glenoid version, inclination, and position on computerized 3-D models of the patient’s scapula. This PSI references the glenoid with 4 feet that captures the edge of the patient’s glenoid at specific locations and is unique because it allows the surgeon to control where on the glenoid edge to 4 feet contact as long as 1 foot is placed on the posterior edge of the glenoid and the remaining 3 feet are placed on the anterior edge of the glenoid. A 3-D model of the glenoid is also provided with this guide.
The Zimmer Biomet patient-specific guide is termed as the Zimmer Patient Specific Instruments Shoulder. Its computer software allows custom placement of the glenoid as well, but it also includes computerized customization of the reaming depth, screw angles, and screw lengths to optimize fixation. Their system includes a central guide pin to set the glenoid baseplate’s location and orientation, a reaming guide to control reaming depth and direction, a roll guide to control the glenoid baseplate’s rotation, and a drill guide to control the screw direction. They also provide a 3-D model of the glenoid.
The Arthrex Virtual Implant Positioning (VIP) System is similar to other systems in that its 3-D planning software is based on CT images uploaded by the surgeon. The unique aspect of this system is that the guide pin is adjusted by the surgeon for each individual patient based on instructions generated by the planning software; however, after use, the instruments are resterilized and reused on subsequent patients (Figures 1A, 1B). In this manner, their instruments are reusable and allow custom adjustment for each patient with the ability to set the pin location and glenoid version in a patient-specific manner. This has the potential benefit of keeping costs down. For more complex deformity cases, the Arthrex VIP System can also 3-D-print a sterile model of the glenoid to help surgeons appreciate the deformity better (Figure 2).
DATA ON PATIENT-SPECIFIC INSTRUMENTS
Several studies have measured the accuracy of patient-specific guides and have compared the accuracy of patient-specific guides to that of traditional methods. Levy and colleagues23 investigated the accuracy of single-use patient-specific guides compared to that of preoperative plans. They used patient-specific guides on 14 cadaveric shoulders based on plans developed by virtual preoperative 3-D planning system using CT images. Once the guide pin was drilled using the patient-specific guide, they obtained a second CT scan to compare the accuracy of the patient-specific guide to the surgical plan generated preoperatively. They found that the translational accuracy of the starting point for the guide pin averaged 1.2 mm ± 0.7 mm, the accuracy of the inferior inclination was 1.2° ± 1.2°, and the accuracy of the glenoid version was 2.6° ± 1.7°. They concluded that patient-specific guides were highly accurate in reproducing the starting point, inclination, and version set on preoperative guides.
Walch and colleagues24 subsequently performed a similar study using 15 cadaveric scapulae without any other shoulder soft tissue or bone attached. They also used CT-scan-based 3-D planning software to plan their glenoid placement with a subsequently fabricated single-use patient-specific guide used to place a guide pin. They obtained a second CT scan after guide pin implantation and compared the preoperative plan with the subsequent guide pin. They found a mean entry point position error of 1.05 mm ± 0.31 mm, a mean inclination error of 1.42° ± 1.37°, and a mean version error of 1.64° ± 1.01°.
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