One of the most common modes of baseplate failure in reverse total shoulder (RSA) is rocking horse loosening resulting from the inability of the fixation to resist upward directed force applied by the humerus.
As pointed out in Factors affecting fixation of the glenoid component of a reverse total shoulder prothesis, the ability of the baseplate to resist the rocking (green arrow) from superiorly directed loading (black arrow) depends in large part on (1) compression of the upper aspect of the baseplate against bone of good quality (yellow arrow) and (2) the pullout resistance of the most inferior screw (red arrow).
As pointed out in Clinical and radiological outcomes with an augmented baseplate for superior glenoid wear in reverse shoulder arthroplasty patients having RSA not infrequently have superior glenoid erosion.
which can be managed by orienting the reamer to preserve the important superior glenoid bone, achieving the desired inferior tilt, and then using a standard glenoid component.
or by reaming along a neutral glenoid axis, sacrificing superior bone, and using an augmented glenoid component to achieve the desired tilt.
A risk with the latter approach is (1) inadequate seating of the baseplate against superior glenoid bone (red arrow) and (2) lack of secure screw fixation in the inferior glenoid bone (red oval).
The authors of the study referenced above aimed to assess the impact of using the metal-augmented glenoid baseplate (AGB) on improving clinical and radiological outcomes, as well as reducing complications, in patients with superior glenoid wear undergoing reverse shoulder arthroplasty (RSA). 24 such patients were propensity matched to 72 patients who received a standard glenoid baseplate (STB) after eccentric reaming (Group B). At 2 year followup patients in both groups were improved with respect to patient reported outcomes, but AGB showed no additional benefit.
Group A experienced more acromial stress fractures (3 cases; 12.5%), whereas Group B had a higher occurrence of scapular notching (24 cases; 33.3%).
Early clinical and radiographic outcomes of an augmented baseplate in reverse shoulder arthroplasty for glenohumeral arthritis with glenoid deformity also noted a high incidence of acromial stress fractures with augmented glenoid components: Acromial stress fractures developed in 11.4% of the patients.
Comment: The value to the patient of the more expensive augmented baseplate was not demonstrated in this manuscript.
No baseplate failure was noted in this two year followup study.
Nevertheless the article provides an opportunity to consider the factors that may increase the risk of rocking horse loosening of the glenoid component in reverse total shoulder.
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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).
Follow on facebook: click on this link
Follow on facebook: https://www.facebook.com/frederick.matsen
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/
Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).
