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Comparison of Ultrasound and MRI for the Diagnosis of Glenohumeral Dysplasia in Brachial Plexus Birth Palsy

Background: In this study, we investigated the agreement between measurements made on ultrasound and those made on magnetic resonance imaging (MRI) in the assessment of glenohumeral dysplasia resulting from brachial plexus birth palsy. Methods: Thirty-nine patients (14 male and 25 female) with brachial plexus birth palsy were evaluated at 2 tertiary care centers. All patients underwent ultrasonography and MRI for suspected glenohumeral dysplasia. Studies were obtained at an average of 2 months apart (range, 0 to 6 months). The average patient age at the time of the initial imaging study was 20 months (range, 4 to 54 months). Four blinded independent evaluators measured the alpha angle, the posterior humeral head displacement (PHHD), and glenoid version on both the ultrasound and MRI study for each patient. The percentage of the humeral head anterior to the scapular axis (PHHA) was determined on MRI only. Measurements were obtained on OsiriX software (Pixmeo). Intraclass correlation coefficients (ICCs) were used to assess the intrarater and interrater reliability, and Bland-Altman plots were used to compare MRI and ultrasound measurement agreement. Results: We found excellent interrater reliability for measurements of the alpha angle on MRI, glenoid version on MRI, and the alpha angle on ultrasound (ICC: 0.83, 0.75, and 0.78, respectively). The interrater reliability for the PHHD on both MRI and ultrasound was good (ICC: 0.70 and 0.68, respectively), and the interrater reliability for the PHHA on MRI was fair (ICC: 0.57). However, the interrater reliability for glenoid version on ultrasound was poor (ICC: 0.30). Relative to MRI measurements, ultrasound measurements were found to underestimate the alpha angle and glenoid version by an average of 13° ± 23° and 6° ± 17°, respectively, and overestimate the PHHD by an average of 4% ± 20%. Increasing patient age corresponded with a significant increase in the MRI-ultrasound measurement difference for the alpha angle (p < 0.01) and a marginally significant increase in the difference for the PHHD (p < 0.06). Conclusions: Measurements on MRI and ultrasound were reliable, with measured bias. The poor agreement between measurements on MRI and ultrasound calls into question the validity of using ultrasonography as a stand-alone modality in the evaluation of glenohumeral dysplasia. MRI remains the gold standard for fully evaluating the glenohumeral joint. The clinical role of ultrasonography may be that of a screening tool or a way of evaluating joint reduction in real time. Level of Evidence: Diagnostic Level I. See Instructions for Authors for a complete description of levels of evidence.