Proximal migration can be measured accurately on standardized anteroposterior shoulder radiographs.

UNLABELLED: During the last decade, investigators of several studies have stressed the importance of early diagnosis and treatment of rotator cuff tears to improve outcome of surgical repair. Proximal migration of the humeral head is thought to be indicative for rotator cuff disorders. We wanted to assess the accuracy of proximal migration measurement on anteroposterior radiographs. Computed tomography scans and anteroposterior radiographs of 43 shoulders in 26 patients were taken using the same protocol. Proximal migration was measured as the acromiohumeral interval and the upward migration index. The mean absolute difference for the upward migration index was only 0.06 (standard deviation, 0.07), this was less then 5% of the mean upward migration index measured on computed tomography reformations. The correlation coefficient and Bland-Altman plot showed a strong correlation between computed tomography and radiographic measurements, especially for the upward migration index (correlation coefficient, 0.82). Our results indicate that measurement of subacromial space on anteroposterior radiographs, controlled for positioning, scaling, and individual differences by using the upward migration index, presents an accurate measurement for proximal migration. LEVEL OF EVIDENCE: Diagnostic study, Level I (testing of previously developed diagnostic criteria on consecutive patients--with universally applied reference "gold" standard). See the Guidelines for Authors for a complete description of levels of evidence.