Quantifying bone loss and lateralization with standardized baseplate versus augmented baseplates.

BACKGROUND

Reverse shoulder arthroplasty continues to be utilized for the treatment of cuff tear arthropathy, glenohumeral degenerative joint disease, and irreparable rotator cuff tears. With advancement in component designs, glenoid retroversion and inclination are now correctable with augmented baseplates. However, quantifying bone loss and lateralization compared to standard baseplates has not been studied. The purpose of the current study is to determine the volume of bone reamed and net lateralization with a standardized baseplate vs. augmented baseplate when glenoid inclination was corrected to neutral.

METHODS

A series of 21 computed tomography scans of patients presenting for shoulder arthroplasty were chosen based on a range of increasing native positive inclination. Computed tomography scans were uploaded into segmentation software and processed. Four fellowship trained shoulder surgeons were then blinded from each other and virtually placed a neutral baseplate and an augmented baseplate for each specimen. Baseplate position was standardized. Additionally, baseplate backside seating of a minimum of 80% was also standardized and glenosphere (nonlateralized) size was selected to eliminate variation in baseplate contact and position. Glenoid inclination was corrected to a minimal of neutral in each specimen as well as glenoid retroversion corrected to <10. Net lateralization from the center of the glenoid to the most lateral aspect of the baseplate was calculated in millimeters.

RESULTS

The mean glenoid retroversion was 8.1 and superior inclination was 10.6 for all specimens. Across all specimens and surgeons, use of a 10-degree augment resulted in similar baseplate backside seating area (219.2 mm vs. 226.2 mm,  > .05). There was substantially lower volume of bone reamed in the augmented baseplate patients (619 mm vs. 1102 mm,  < .001). Larger standard deviation seen in the augmented baseplate columns are attributed to differences in surgeon preference for percent backside seating, which was standardized at a minimum of 80%. Use of a 10-degree full wedge augment resulted in 2.4 mm additional glenoid lateralization than a neutral baseplate on average across all included scapulae.

CONCLUSION

The current study demonstrates approximately 50% less bone removal and 2.4 mm of true lateralization with a 10-degree augmented baseplate when compared to standard baseplates.