A Novel Method to Measure Superior Migration of the Humeral Head: Step-off of the C-line

ABSTRACT

BACKGROUND: Superior migration of humeral head has been conventionally determined by measuring the acromiohumeral distance (AHD), We sought to devise a novel measurement system more reliably and accurately than AHD. We described a structural landmark called 'C-line'. In this study, we investigated the clinical usefulness of 'step-off of the C-line (SOC)' compared to that of AHD. METHODS: The C-line formed from the medial margin of the proximal humeral head continuing up to the inferior margin of the articular glenoid and then to the lateral border of the scapula. The superior migration of the humeral head triggered by a rotator cuff tear introduces a discontinuity in this C-line. We measured the distance of this discontinuity. We enrolled 144 patients who underwent a rotator cuff repair. We selected 58 controls who didn't have any cuff lesions apparent on magnetic resonance imaging. Using radiographs derived from standardized true anteroposterior views of the shoulder, we measured the SOC and the AHD. We used t-tests for statistical analyses. RESULTS: A rotator cuff tear was associated with an increase in SOC and a decrease in AHD. In control group, the mean SOC was 1.29 ± 1.71 mm and AHD was 9.71 ± 2.65 mm. In cuff tear group, the mean SOC was 3.15 ± 3.41 mm and AHD was 8.28 ± 1.76 mm. The mean SOCs of the patient group in relation to the mean SOC of the control group according to tear size, the SOCs of medium tear and lager groups showed statistically significant increase (p<0.05). CONCLUSIONS: The SOC may be a similarly effective to diagnose cuff tears of medium size and larger compared with AHD.