Thursday, November 3, 2016

MRI or CT for evaluating glenoid pathoanatomy (or neither)

Magnetic resonance imaging is comparable to computed tomography for determination of glenoid version but does not accurately distinguish between Walch B2 and C classifications

In this study, three surgeons compared the accuracy of MRI to that of CT for assessment of glenoid version and Walch classification in 30 patients with primary shoulder osteoarthritis.

Here is an example, the authors provided.

"Comparison between (A) computed tomography (CT) and (B) magnetic resonance imaging (MRI) axial slice views of the same glenohumeral joint at approximately equivalent axial position. In this example, glenoid biconcavity is more evident on the CT scan, thereby enabling observers to properly identify the glenoid as a Walch type B2. On MRI, however, the glenoid could be subjectively interpreted as a Walch type C because of severe retroversion and much subtler presentation of biconcavity."
Mean glenoid version was −15.5° and −18.6° by CT and MRI, respectively (P = .17). 

They found that MRI was largely comparable to CT scan for evaluation of the glenoid, with similar measurements of version and identification of less extreme Walch glenoids. However, MRI was less accurate at distinguishing between type B2 and C glenoids.

Comment: While these authors assert that computed tomography (CT) scan is the standard for the preoperative assessment of glenoid version and morphology before total shoulder arthroplasty, they suggest that "the incentives for omitting a CT scan arise from the obligation to reduce costs and to avoid unnecessary exposure of patients to ionizing radiation." We agree.

 We have found that the plain film axillary 'truth' view (see this link and this link

almost always provides the necessary and sufficient information to classify the pathology and plan the treatment of the arthritic glenohumeral joint, eliminating the cost of either a CT scan or an MRI scan. We are unaware of evidence showing that patients having preoperative CT or MRI scans have better clinical outcomes than those with only plain film imaging that includes the 'truth' view.