Correlation of the Rotator Interval on Direct CT Arthrography in Shoulder Instability Patients with External Rotation Stress Radiographs

Purpose To correlate rotator interval dimensions on direct CT arthrography (CTA) with external rotation shoulder stress radiographs in patients with shoulder instability. Materials and Methods One hundred and twenty-three shoulders of 115 patients with shoulder instability that underwent direct CTA and shoulder stress radiographs in neutral position and external rotation were enrolled. Axial, oblique coronal, oblique sagittal CT images were obtained after intra-articular contrast injection. Width and depth of rotator interval on sagittal CTA images were evaluated and acromiohumeral (AH) distance on neutral and external rotation stress radiographs were measured. CTA measurements were compared with AH on stress radiographs according to the group with or without "external rotational instability". Results Out of 123 shoulders, 79 with external rotation instability showed increased or unchanged AH distance on external rotation compared with neutral position. Width of rotator interval was 2.43 ± 0.31 cm and depth was 0.87 ± 0.2 cm. Forty-four shoulders without external rotation instability showed decreased AH distance on external rotation compared with neutral position. Width of rotator interval was 2.02 ± 0.45 cm and depth was 0.75 ± 0.2 cm. Width and depth of rotator interval were significantly greater in the external rotation instability group. Conclusion Width and depth of rotator interval on CTA were significantly correlated with AH distance on external rotation stress radiographs.