Friday, July 15, 2016

Reverse total shoulder arthroplasty - tilting the baseplate

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

These authors point out that 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. They evaluated 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 were 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. 

They suggest that three-dimensional preoperative planning software may be useful for glenoid baseplate positioning in reverse shoulder arthroplasty.

Comment: Our practice is to obtain a preoperative true anteroposterior radiograph in the plane of the scapula and then use that image to envision a line perpendicular to the glenoid center.  At surgery, the drill for the central screw of the baseplate is oriented by eye with a slight inferior tilt in reference to this perpendicular to the glenoid center. No guides or special instrumentation is used. In cases where the preoperative true anteroposterior radiograph in the plane of the scapula indicates a superior inclination of the perpendicular to the glenoid center, the angle of the drill is adjusted accordingly.

This approach is shown for the left and right shoulders of a patient having had a failed hemiarthroplasty on one side and pseudo paralysis on the other. 

Our approach to reverse total shoulder arthroplasty is shown in this link. Our goal, whenever possible, is a cementless impaction grafted humeral stem with a 135 degree angle and a laterally offset glenopshere securely fixed with screws in the high quality bone at the base of the subscapularis fossa with minimal inferior placement to avoid excess tension on the acromion and the brachial plexus. The use of a glenosphere with lateral offset makes the exact inclination of the component less critical.


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