Accuracy of the Subchondral Smile and Surface Referencing Techniques in Reverse Shoulder Arthroplasty

Inferior glenoid baseplate tilt relative to the coronal axis of the scapular body has been associated with improved results and fewer postoperative complications in reverse shoulder arthroplasty. However, the native glenoid surface is not always a reliable reference for the true scapular axis. Digital preoperative planning software and advanced imaging now allow surgeons to more precisely determine optimal glenoid placement. The purpose of this study was to evaluate the accuracy of the subchondral smile and cannulated surface guide techniques in achieving inferior glenoid baseplate tilt by using 3-dimensional preoperative planning software. Virtual glenoid baseplate preparation and implantation was performed using computed tomography scans of 16 shoulders with rotator cuff deficiency. Two techniques were used: a subchondral smile technique that preferentially reams the interior glenoid, resulting in the appearance of a smile, and a cannulated surface guide technique that references the native glenoid face to place the baseplate in 10° of inferior tilt. Using the subchondral smile technique, the glenoid baseplate was implanted at a mean of 8.9° of superior tilt relative to the transverse scapular axis. Using the surface guide technique, the glenoid baseplate was implanted at a mean of 2.8° of superior tilt. Neither the subchondral smile technique nor the 10° cannulated surface guide technique is a reliable method to produce inferior glenoid tilt relative to the transverse axis of the scapula. Three-dimensional preoperative planning software is a useful tool when attempting to achieve optimal glenoid baseplate positioning in reverse shoulder arthroplasty. [Orthopedics. 2016; 39(4):e615-e620.].