Friday, February 5, 2016

Preoperative imaging of the arthritic shoulder: the glenoid inclination angle

These authors explore methods for measuring the glenoid inclination angle ( β-angle), formed by the intersection of a line on the floor of the supraspinatus fossa and glenoid fossa line.

In 51 shoulders they compared measurements on (1) an anteroposterior (AP) x-ray view of the shoulder, (2) unformatted 2-dimensional (2D) computed tomography (CT) scan, and (3) reformatted 2D CT scan in the scapular plane to their 'gold standard': glenoid inclination angle calculated by the 3D software.

The mean differences from the gold standard was 
1° (SD), 0.5°) for the β-angle measured on reformatted CT scans
3° (SD, 0.7°) for the  β-angle measured on AP plain radiographs and
10° (SD, 0.9°) for the β-angle measured on unformatted 2D CT scans 

The incremental costs and time for the CT scan with reformatting are not presented, so that the value (benefit/cost) of the two degrees of increased accuracy in comparison to plain films cannot be determined.

Comment: While there is no question that measurements of pre and postoperative glenoid orientation are of interest, the paper's statement that "An accurate measurement method for preoperative glenoid inclination is essential for intraoperative decision making to maximize implant longevity and function" has yet to be documented.
We find that the necessary and sufficient information for the planning and conduct of shoulder arthroplasty can be gained from the economical standardized AP view in the plane of the scapula

and the standardized axillary view taken with the arm elevated 90 degrees in the plane of the scapula (position of function).


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