While some authors have stated that scapular notching (the erosion of the lateral scapula from contact with the humeral component of a reverse total shoulder) is not of clinical importance, there are patients where it is of obvious clinical consequence.
Here is the x-ray of a lady with a failed prosthesis for fracture. Note the superior displacement of the humeral head, the long cemented stem and the poor quality of the glenoid bone.
Her surgeon converted her to a reverse total shoulder with bone graft around the humeral component and a Grammont-style prosthesis
At two years after surgery, she had increasing shoulder pain and these films showing bone loss at the inferior aspect of her glenoid along with some evidence of contact between the lower screw and the humeral component.
Her most recent films show progressive loss of the bone supporting the glenoid component.
While this patient has yet to undergo a revision, we suspect that her humeral component may look like this.
This is a good time to review the article:
Anytime we have unintended contact between high density polyethylene and bone, it is a problem. Scapular notching is a radiographic finding, but the real concerns are about (1) the damage to the poly of the humeral cup, (2) loss of the bone of the scapula that supports the glenoid component, and (3) the potential for instability resulting from leverage of one against the other. See this previous post which discusses this phenomenon in some detail.
In the Grammont-type reverse total shoulder, contact of the adducted humeral component against the scapula is not uncommon as shown in these figures from a manufacturer's website (arrow inserted by us to show point of contact when the arm is brought to the side).
These authors retrospectively reviewed 448 patients who underwent a Grammont-type reverse total shoulder (461 shoulders) performed for rotator cuff tear arthropathy or osteoarthritis with cuff deficiency with a mean followup of 51 months (range, 24-206 months). They found notching of the scapula in 68% of the cases; it was present in 48% at one year after surgery.
Notching was more common in active patients, in patients with cuff tear arthropathy, and in patients with greater degrees of superior displacement of the humeral head before surgery. Strength and range of motion were compromised in patients with notching.
Importantly, 36% of shoulders with notching had humeral radiolucent lines (in contrast to 17% in those without notching), suggesting the possibility that polyethylene particles from the humeral cup causing bone resorption. Similarly glenoid loosening was three times more common in the presence of notching.
The authors point out that standardized plain x-rays are necessary for the evaluation of notching, noting that sometimes notching is better seen on the axillary view.
Comment: Scapular notching is important and can be expected to adversely affect the long term durability and function of the reverse. It is best avoided by (1) use of a glenoid component design that offsets the center of rotation from the scapula, (2) proper positioning of the glenoid component at the inferior aspect of the glenoid, (3) avoiding superior tilt of the glenoid component, and carefully checking for contact between the humeral component and scapula at surgery when the arm is adducted and rotated (see below).
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