The correlation of supraspinatus outlet view with computed tomography for visualization of the anterior acromial undersurface

Introduction Understanding the real shape of the undersurface of the acromion prior to acromioplasty is indispensable. Today, Supraspinatus outlet view (SSOV) is a standard view used to determine the shape of the anterior acromion. Three types of acromial undersurface were described by Bigliani and Morrison. The purpose of this study was to find out whether the real acromial type can be visualized on X-ray SSOV and compare the shape of the anterior undersurface of the acromion visualized on SSOV, with the shape revealed on 2D CT reconstructions. Methods The SSOV X-rays and CT scans of 30 consecutive patients suffering from rotator cuff dysfunction were retrospectively analyzed. The shape of the acromion visualized on plain X-rays was classified according to Bigliani and Morrison classification system. Two-dimensional CT reconstructions were performed, reproducing the lateral, middle, and medial sections of the acromion. The acromial type that was visualized on each of those reconstructions was separately classified according to the Bigliani and Morrison system. A complete profile of the acromial undersurface was constructed from the integration of acromial types seen on each CT section. The acromial morphology seen on X-rays and CTs was compared. Results A total of 30 patients comprised the study cohort; mean age was 57 (STD = 8.5) years. Three Type I, 22 Type II, and 5 Type III acromions were visualized on the SSOV X-rays. CT reconstructions revealed seven different morphological acromial profiles (I,I,I; I,II,II; I,II,III, etc.), which we divided into 3 groups: (1) Uniform (30%), (2) Internally curved (20%), and (3) Internally hooked (50%). The acromial type visualized on X-ray correlated with the acromial type on at least one CT section in all of the cases. In the case of uniform acromial profile, there is a full correlation between the acromial type visualized on X-rays and the type visualized on CT. In non-uniform profiles, there was an incomplete correlation between the types of the acromion visualized on SSOV and CT. SSOV X-rays correlated with or underestimated, but never overestimated, the acromial morphological type. Discussion The curved or hooked portion of the acromial undersurface is not always visualized on the SSOV. On X-rays, the middle and lateral sections are seen more accurate than the medial section. Conclusion Surgeons should be aware that SSOV X-rays may underestimate the true type of the acromial undersurface.