Lateralized reverse total shoulder: abduction damage to the acromion

Lateralization of a reverse total shoulder is used by some surgeons with the goal of enhancing stability, improving strength, and reducing scapular notching.

One of the potential drawbacks of this approach is unwanted contact between the tuberosity and the undersurface of the acromion when the arm is abducted.

The authors of Subacromial notching after reverse total shoulder arthroplasty suggest that damage to the acromion may be caused by abduction impingement after reverse total shoulder arthroplasty (RSA) with a lateralized design. They reviewed the medical records of 125 patients who underwent RSA with the design shown below

They defined subacromial notching (SaN) as subacromial erosion observed at the final follow-up but not on the X-ray three months after surgery. They found that SaN occurred in 12.8% (16/125) of enrolled patients. Greater postoperative humeral lateralization offset (HL) was a risk factor for subacromial notching.

The VAS and ASES scores at the final follow-up were significantly worse in patients with subacromial notching. 

Comment: Contact between the greater tuberosity and the acromion can limit the range of abduction and can weaken the acromion.

On AP radiographs it is straightforward to see the risk of acromion-tuberosity contact. 

First, fit a circle to the glenosphere

then draw a line segment from the center of the glenosphere to the tip of the tuberosity

finally draw a second line segment of the same length from the glenosphere center to the acromion and note whether there would be contact in abduction.

Of course it is desirable to check for this unwanted contact while surgical the incision is still open. This can be simply done by abducting the arm to see if the tuberosity clears the acromion. If it does not, it may be possible to avoid unwanted contact by shaving bone from the tuberosity. If this is insufficient, the surgeon can consider modifying the implant or its position.

You can support cutting edge shoulder research that is leading to better care for patients with shoulder problems, click on this link.

Follow on twitter: https://twitter.com/shoulderarth
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).