MRI may be used to determine shoulder instability, glenoid bone loss
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KOLOA, Hawaii — MRI can be used to determine the chronicity, severity and location of traumatic shoulder instability, while glenoid measurements on either CT or MRI can evaluate bone loss and treatment, according to a presenter here.
In her presentation at Orthopedics Today Hawaii, Pamela J. Lund, MD, noted published research has shown MRI and magnetic resonance angiography (MRA) have good sensitivity and specificity for identifying labral tears, which are the hallmark of shoulder instability, but there is not a lot of data comparing MRI, MRA and 3 Tesla MRI.
“Just remember, these low-field imaging, at least the older ones, were not good for the labrum, so don’t rely on them for looking for your labral tears,” Lund said.
If performing shoulder arthrography, Lund noted CT arthrogram uses iodine and the MR arthrogram uses gadolinium. Although the abduction and external rotation (ABER) view is routinely used for MR arthrography studies, Lund said an oblique view from posterior to anterior is substituted for patients who cannot do the ABER view.
When it comes to the anatomy, Lund said surgeons should not be concerned about the intermediate signal between the labrum and the articular cartilage, as it is not a tear.
“One thing about the nomenclature, you will see some radiologists call 3 o’clock and 9 o’clock. They switch them for right and left,” Lund said. “My convention is to say 3 o’clock is always anterior and 9 o’clock is always posterior. I think it becomes confusing when you are trying to switch them back and forth, even though it is absolutely anatomically correct. The anterior glenoid is certainly different to the posterior glenoid.”
Recently published studies showed that use of either CT or MRI with the best-fit circle method is accurate for measuring glenoid bone loss, according to Lund. She added measurement for glenoid bone loss has to be bilateral, and that use of the surface area method can be easily performed for measuring Hill Sachs lesion and glenoid bone loss.
“It isn’t as simple as measuring the Hill Sachs and the glenoid bone and saying, ‘Oh, one is bigger than the other,’” Lund said. “You have to take into some consideration the functional anatomy of the shoulder. So, in the externally rotated functional position, there is only about 0.83% of that glenoid available, so we have to correct for that. What we do is take the best-fit circle times 0.83, and then we subtract our glenoid bone loss.”
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Lund PJ. MRI evaluation of shoulder instability. Presented at: Orthopedics Today Hawaii. Jan. 8-12, 2023; Koloa, Hawaii.
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