Saturday, May 26, 2018

Why is so much money and time being spent on detailed measurements of glenoid version?

Comparative analysis of 2 glenoid version measurement methods in variable axial slices on 3-dimensionally reconstructed computed tomography scans

These authors analyzed the variation of the glenoid vault compared with the Friedman angle according to different CT slice heights and angulations in 60 shoulder CT scan reconstructions.
Seven axial slices of different heights and coronal angulations were selected, and measurements were carried out by 3 observers. 

Mid-glenoid mean version was −8.0° (±4.9°; range, −19.6° to +7.0°) and −2.1° (± 4.7°; range, −13.0° to +10.3°) using the vault method and Friedman angle, respectively. Increasing slice height or angulation significantly increased anteversion for the vault method (P < .001). Both interobserver reliability and intraobserver reliability were significantly higher using the Friedman angle. 

They concluded that "the vault method shows less reliability and more variability according to slice height or angulation. Yet, as it significantly differs from the Friedman angle, it should still be used in situations where maximum bone purchase is sought with glenoid implants. For any other situation, the Friedman angle remains the method of choice".

Comment: While this paper asserts that preoperative measurement of glenoid version "is crucial for proper surgical implant positioning", it shows that with CT reconstruction there is substantial variability depending on which CT slices are used in the measurement and on the method of angle measurement.

It has not been demonstrated that patients having expensive CT reconstructions preoperatively have better outcomes than those having a standardized axillary "truth" view (see this link) - which is less costly, less time consuming and gives the patient 1/26th the radiation.

Even in complex pathologies, the axillary "truth" view gives us all the information we need for discussing the situation with the patient and for planning the procedure.

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