Saturday, March 16, 2013

Glenoid version - MRI vs axillary view

Magnetic resonance scanning vs axillary radiography in the assessment of glenoid version for osteoarthritis

Glenoid version is an important characteristic of many arthritic shoulders; it affects the conduct of the surgery and is thought to increase the risk of glenoid component loosening in total shoulder arthroplasty.

While authors have proposed that 'normalizing' glenoid version improves outcome of total shoulder arthroplasty in retroverted glenoids, this has yet to be demonstrated clinically.

These authors assessed the utility of magnetic resonance imaging (MRI) for the assessment of glenoid version in glenohumeral osteoarthritis compared with standard plain axillary radiography (AXR).

The mean glenoid version measured was -14.3° on MRI and -21.6° on AXR (mean difference, -7.36°; P < .001). Intraobserver and interobserver reliability coefficients were 0.96 and 0.9, respectively, for MRI and 0.8 and 0.71, respectively, for AXR.

Thus in the hands of these authors, MRI offers a more precise method of determining glenoid version compared with x-ray imaging.  The question is does the increase in precision justify the cost of the MRI (at least $1000 in most settings)? In an era where we must be concerned about health care costs, is this the way we want to spend the health care dollar? Are the differences of any clinical significance?

If we look at their graph comparing the version on MRI vs that on an axillary view, we see a strong correlation (r=.65) between the two methods. How likely is it that the surgeon would have made an error if only the axillary view data were available?

The axillary radiographs in this study were not rigorously controlled. In our experience, a standardized axillary radiograph provides an excellent view of the details of glenohumeral pathoanatomy, including glenoid type, version, and point of glenohumeral contact. 

Finally, it is important to recognize that the position of the arm and scapula were quite different for axillary radiographs and the axial MRI scans, so it not at all clear that the differences are indicative of a lack of accuracy of the axillary view.

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