These authors point out that secure glenoid baseplate fixation is essential for a successful reverse total shoulder (RSA). In cases of glenoid bone loss, use of the anatomic glenoid center line may not provide sufficient bone support for fixation. Anteversion of the baseplate and central screw fixation along the alternative center line is a described method for achieving baseplate fixation in such cases.
The authors comparde the outcomes of RSA using the anatomic or alternative center line using a retrospective case-controlled study. 66 patients treated with the anatomic center-line technique
for baseplate fixation were matched 3:1 based on sex, indication for surgery, and age with 22 patients treated with the alternative center-line technique. The mean age was 74.2 years (range, 58-89 years) and mean follow-up period of 53 months (range, 24-130 months).
A monoblock central-screw glenoid baseplate was used in all cases. One of the features of this design is that the preponderance of the fixation is provided by a large central compression screw.
In cases in which the anatomic center line was used, the baseplate was inserted along the standard glenoid center line. Alternative center-line placement of the baseplate was used to achieve primary baseplate
fixation in cases in which it was determined preoperatively or intraoperatively that there was inadequate bone to support fixation of the center screw.
If <80% coverage of the baseplate could be obtained on host bone, structural grafting with either humeral head autograft or femoral head allograft was used to augment baseplate support as shown in the case below.
Attempts were made to achieve secondary fixation by resting the peripheral rim of the glenosphere on the host glenoid bone or bone graft to distribute the load observed through the baseplate fixation.
Often, a glenosphere with a lip extension was used to achieve this goal (glenosphere sizes of 36 mm – 4, 40 mm neutral, and 40 mm – 4).
Postoperatively, all patients were managed with the same rehabilitation protocol consisting of wearing a shoulder immobilizer with a self-directed therapy protocol focused on only pendulum exercises for the first 6 weeks, followed by an activeassisted stretching program. Strengthening and lifting were delayed for 3 months.
At the final follow-up, they found no significant differences in patient reported measures, including the Simple Shoulder Test score, American Shoulder and Elbow Surgeons score, visual analog scale pain score, and Single Assessment Numeric Evaluation score.
The overall improvements in these measures and all active motions and functional tasks of internal rotation were not different.
No radiographic evidence of glenoid loosening was found in either group.
Two patients in each cohort (3% of the anatomic group and 9% of the alternative group) experienced an acromial fracture.
Low-grade scapular notching developed in 15.2% of the anatomic group and 18.2% of the alternative center line group.
Comment: This report demonstrates that - in experienced hands - placing the central screw in the thickest part of the glenoid neck can provide good fixation if coupled with bone grafting when adequate support by native bone cannot be achieved.
We have found it useful to use a small diameter drill to confirm the orientation that will provide the maximum (ideally 3 cm) of screw fixation.
While the surgeon attempted to achieve secondary fixation by resting the peripheral rim of the glenosphere on the host glenoid bone, it is important that this contact not interfere with complete seating of the glenopshere on the baseplate.
As the authors point out, these results may not be generalizable to practitioners who have less experience or those who use other reverse shoulder devices, such as those without a central compression screw (see an example of such an implant below).
