It's a pleasure and an honor to be here today. My name is Mason Yoder. I'm a first-year resident at the University of Michigan. I'm here to present a study that I did during my medical training at the University of Cincinnati in conjunction with the Cincinnati Children's Hospital. The other authors on the study were Colin McDonald and Chantal Parikh. And the title of our study is Measurements for Objective Diagnosis of Multidirectional Instability of the Shoulder in Adolescent Patients. The authors have no disclosures. Brief introduction to MDI. So MDI, or multidirectional instability, is a diagnosis in which a patient has instability of their shoulder in multiple directions, with at least one being in the inferior directions. This is a clinical diagnosis based off of patient history and physical exam maneuvers. One of those maneuvers is actually shown here, called the sulcus sign, where you apply inferior traction to the arm and you see a dimple appear lateral to the acromion. Because this is a clinical diagnosis, it's often difficult to make because of inter-examiner variability in their physical exam interpretation skills. So most patients with MDI have no identifiable labral or capsular tear pattern on MR imaging. However, it's hypothesized that—we hypothesize that there might be a laxity of the capsule and that you might be able to use that as an objective—to objectively distinguish MDI from other sorts of shoulder instability. So the purpose of this study was to identify objective criteria for MDI diagnosis in adolescent patients based on shoulder capsular dimensions on MR imaging. This is a retrospective comparative study. We reviewed the medical records and MR arthrograms of patients treated for shoulder instability at the Cincinnati Children's Hospital between the years of 2008 to 2019. In our study, we had 24 patients, or 28 shoulders, that were surgically treated for MDI, and we matched these with 25 patients, or 27 shoulders, who were treated for anterior shoulder instability due to bank cart tears, and then we used this as our control group for comparison. The imaging analysis for our study, we used MR arthrograms in the sagittal oblique view. We looked at two different windows. So the first, on figure 1 on the left, was the sagittal oblique view of the rotator interval. We defined this as the image in which you could first see the coracoid process. We measured the depth of the rotator interval, defined as the roof of the rotator interval to the head of the humeral head, and then the width, defined as the superior border of the subscapularis tendon to the anterior border of the supraspinatus tendon. Likewise, on figure 2 on the right, we measured the glenohumeral capsule. So this was defined as the articular surface of the glenoid, and we drew four lines through this structure to identify an anterior, posterior, posterior-inferior, anterior-inferior, and inferior dimension of that capsule. Next, we compared these measurements between these two groups using students' t-tests, and for the variables that were significantly different, we used receiver-operator curves to identify threshold values and then calculate specific sensitivities and specificities for identifying MDI amongst those patients. Our study was powered so that 16 patients were predicted to detect a difference of 5 millimeters with an 80% power. The MDI group consisted of 20 females and 4 males with a mean age of 15 years, and the control group consisted of 9 females and 16 males with an age of 15.4 years. Of note, there were more females in the MDI group than the control group. The results of this study showed that the rotator interval depth was significantly different between these two groups, with the rotator interval depth being wider in the MDI group. Likewise, the posterior-inferior and posterior-inferior capsular dimensions were also wider amongst the MDI group with these specific measurements here. For our receiver-operator curve analysis, we found that the two variables that gave the highest sensitivity and specificity were, first, rotator interval depth, which, measured at a threshold of 7.4 millimeters, had a sensitivity of 73.5% and specificity of 70.4%, and the second variable being the inferior capsule, which, when measured at a threshold value of 24 millimeters, had a sensitivity of 70.6% and specificity of 70.4%. We remember this by the term 24-7. So to conclude, a 24-millimeter and 7.4-millimeter threshold, 24-7, of the inferior capsule and rotator interval depth, respectively, on shoulder MR arthrography could aid in the diagnosis of MDI in adolescent patients. This is the first study to objectively quantify capsular volume in adolescent patients with surgically treated MDI, and further studies could validate this in a prospective fashion. Thank you very much. It's been a pleasure.

Mason Yoder

University of Michigan

University of Cincinnati

Multidirectional Instability of the Shoulder

MRI imaging