Os acromiale: frequency, anatomy, and clinical implications.

Area of Science:

• Orthopedics and Anatomy
• Human Osteology
• Skeletal Biology

Background:

• Os acromiale is an anatomical variant where the acromion has separate ossicles, occurring in 1-15% of the population.
• Previous studies suggest a link between os acromiale and subacromial impingement, but lack comparative frequency data.
• Inconsistencies in literature regarding os acromiale's anatomy, development, and prevalence necessitated this anatomical investigation.

Purpose of the Study:

• To accurately determine the frequency of os acromiale in the general population.
• To describe the anatomical characteristics of os acromiale.
• To investigate potential racial and sexual variations in os acromiale prevalence.

Main Methods:

• Examination of 2,367 scapular bones from 1,198 human skeletons (Hamann-Todd Osteological Collection).
• Analysis included specimens from 1,033 men and 165 women, spanning ages 18-89.
• Frequencies were recorded, specimens measured, and os acromiale differentiated from normal acromial development.

Main Results:

• Os acromiale was identified in 8.0% of skeletons (96 out of 1,198), with bilateral occurrence in 33.3% of affected individuals.
• The condition was significantly more frequent in Black individuals (13.2%) compared to White individuals (5.8%) (p < 0.001).
• Os acromiale was also more frequent in men (8.5%) than women (4.9%), though not statistically significant (p = 0.09).
• Fused os acromiale, previously undescribed, was identified and may be misdiagnosed as a free ossicle on radiographs.

Conclusions:

• Os acromiale occurs in 8.0% of the population, with variations based on race and sex.
• A previously undescribed fused variant of os acromiale can mimic free ossicles on radiographic imaging.
• This study provides a clearer understanding of os acromiale's frequency and anatomical presentation.