Three-Dimensional Templating and Use of Standard Instrumentation in Primary Anatomic Total Shoulder Arthroplasty.

INTRODUCTION: Three-dimensional (3D) templating of the glenoid in anatomic shoulder arthroplasty allows for more accurate planning and more optimal positioning of the glenoid component than 2-dimensional computed tomography (2D CT) scans through an improved understanding of both the pathologic and the premorbid glenoid joint line, version, and inclination in reference to an idealized calculated glenoid position. STEP 1 OBTAIN A CT SCAN WITH 3D RECONSTRUCTION AND DEFINE GLENOID VERSION AND INCLINATION: Obtain a CT scan of the entire scapula and proximal part of the humerus with slices of ≤1 mm and a 3D reconstruction with subtraction of the humeral head, and identify the scapular and glenoid planes to define the pathologic version and inclination, which can be done in any commercially available software program while following these basic principles (Video 1). STEP 2 DEFINE PREMORBID GLENOID MORPHOLOGY: Carefully evaluate for the presence of the native glenoid, noting its version and inclination, and be careful to distinguish the true native glenoid from osteophytes (Video 2). STEP 3 PLACE THE VIRTUAL IMPLANT: Place the virtual glenoid component to restore the premorbid glenoid anatomy (Video 3). STEP 4 EVALUATE THE NEED FOR AN AUGMENTED GLENOID COMPONENT BONE GRAFT OR ECCENTRIC REAMING: In the presence of bone loss from posterior glenoid wear, assess the need for an augmented glenoid component, bone graft, or eccentric reaming to achieve adequate backside seating (Video 4). STEP 5 NOTE THE CENTER PIN POSITION AND TRAJECTORY: Once the glenoid component has been templated, note the starting location and trajectory of the center pin used for cannulated glenoid reaming and bone preparation (Video 5). STEP 6 REMOVE REMAINING CARTILAGE AND SOFT TISSUE FROM THE GLENOID SURFACE: Intraoperatively, remove remaining labrum and any remaining cartilage or soft tissue, and expose the glenoid periphery to clearly define the osseous anatomy, including the base of the coracoid, such that it mirrors what the 3D CT scan and preoperative plan display (Video 6). STEP 7 PLACE THE CENTER PIN ACCORDING TO THE PREOPERATIVE PLAN: Place the center pin for glenoid preparation in the previously templated location and trajectory to emulate the surgical plan defined in the software (Video 7).
RESULTS: We performed a prospective, randomized controlled trial of positioning of the glenoid component in anatomic TSA using preoperative planning with 3D CT scans and standard instrumentation compared with using 3D CT preoperative planning with patient-specific instrumentation29.