Validation of the inter‑individual variability of the angulus acromialis (acromial opening angle) and its clinical relevance.

Abstract

Background: The acromial opening angle is the angle whose apex corresponds to the angulus acromialis, formed by the junction between the spine of the scapula and the lateral edge of the acromial process. There are 3 different morphologies: C-shaped, L-shaped and with a "double angle". We hypothesis that the distribution of the acromial opening angle in a population was Gaussian and was not influenced by the shape of the angulus acromialis.

Methods: Based on 103 dry cadaveric scapulas were determined the angle AÔB as: The crossing point between the spine of the scapula and the medial edge of the scapula (point A), The tip of the angulus acromialis (point O), the lateral edge of the acromion (point B). The shape of the angulus acromialis were noted.

Results: The series consisted of 62 (60%) left scapulas and 41 (40%) right scapulas. The shape of the angulus acromialis was: L shape: 47 (45.6%), C shape: 51 (49.5%), and double angle shape: 5 (4.8%). The average angulus acromialis was 105° (87.8°-124.9°; +/- 7.1°). The acromial opening angle as a function of the L, C and "double angle" shape was respectively 104.2° (87.8°-119.8°; +/- 7.3°), 105.7° (89.8°-124.9°; +/- 6.9°), 106.1° (98°-116.7°; +/- 8.6°). There was no significant difference in angulus acromialis as a function of side (p = 0.95) or acromion shape (p = 0.54).

Conclusion: The average angulus acromialis is 104.9°. Variations in this angle modify the lateral offset of the acromion on plain radiographs, while the width of the acromion remains unchanged. It also modifies the posterior portal for shoulder arthroscopy.