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Shear forces likely significantly higher in the maximum circular plane
When the glenoid component is positioned in the maximum circular plane, shear forces are significantly higher compared with the inferior circle plane, and researchers found this occurrence is more pronounced in early abduction, according to study results.
Researchers evaluated the CT scans of 152 healthy shoulders scanned for pathology at the contralateral side. After positioning a virtual glenoid component in both the maximum circular plane and the inferior circle plane, the researchers measured the inclination of both planes as the intersection with the scapular plane.
Overall, there were 72 women and 80 men included in the study, with a mean age of 41.8 years. Excellent intraobserver and interobserver variability was observed for all parameters, according to the researchers.
The researchers observed a radius of 16 mm from the maximum circle and of 13 mm from the inferior circle. According to study results, the glenoid inclination of the component positioned in the maximum circular plane and the glenoid retroversion averaged 95°, whereas the inclination of the component positioned in the inferior circle plane averaged 111°, with a retroversion of 93°.
The researchers calculated a 98% reduction in 60° abduction to a 49% reduction in 90° of abduction in shear forces for the glenoid component in the inferior circle plane vs. the maximum circular plane.
According to the researchers, the positioning of the glenoid component within the inferior circle may help decrease the risk of rocking horse phenomenon. – by Casey Tingle
Disclosure: The researchers report no relevant financial disclosures.