Sammarco, J Bone Joint Surg Am 2000 - Os Acromiale: Frequency, Anatomy, and Clinical Implications - Article Summary

Os Acromiale: Frequency, Anatomy, and Clinical Implications

Sammarco·J Bone Joint Surg Am·2000·188 citations·Anatomic study

Background

Os acromiale is present when the anterior portion of the acromion has one or more separate ossicles. Its frequency has been documented, in radiographic and anatomical studies, to be between 1 and 15 percent. Reports of os acromiale associated with subacromial pathology have been cited to imply that this entity is a cause of subacromial impingement; however, no study has demonstrated an increased frequency of os acromiale in patients with shoulder pain compared with the frequency in the general population. Inconsistencies in the literature concerning anatomy, development, and frequency prompted the current anatomical study. The purpose of this study was to better define the frequency and anatomy of os acromiale in the general population.

Methods

Two thousand three hundred and sixty-seven scapular bones from 1198 human skeletons from the Hamann-Todd Osteological Collection were studied for evidence of os acromiale.
The sample consisted of specimens from 1033 men and 165 women, 843 of whom had been white and 355, black.
The mean age of the individuals at the time of death was 44.7 years (range, 18 to 89 years).
The frequency of os acromiale was noted, and the specimens were measured.

Results

There were 128 cases of os acromiale in 96 (8.0 percent) of the 1198 skeletons, and the condition was bilateral in 32 (33.3 percent) of the 96 skeletons.
In 20 cases, the free fragment had been lost but it was assumed that a fragment had been present because the acromion was truncated.
Os acromiale was more frequent in blacks than in whites (13.2 compared with 5.8 percent; p < 0.001) and in men than in women (8.5 compared with 4.9 percent; p = 0.09).
The mean proportional length of the free fragment was 0.42 compared with the overall length of the acromion.
Care was taken to differentiate os acromiale from a normal immature acromion.
6 skeletons demonstrated persistent acromial apophyses.
All 6 cases were bilateral; 7 fragments were fusing, and 5 were free.
The oldest age at which a persistent normal apophysis was found was 21 years.
The frequency of os acromiale in specimens from individuals who had been less than 22 years old was not significantly different from that in the remainder of the collection (p = 0.74).
21 scapulae had a distinct circumferential line that was suggestive of an acromial joint, but the distal and proximal portions were solidly fused.
However, the findings on plain axillary radiographs of 16 of these specimens were indistinguishable from those of specimens with os acromiale.

Conclusions

An anatomical study, performed to better define the frequency and anatomy of os acromiale in the general population, showed that fused os acromiale, which has not been described previously, might be mistaken for a free ossicle in the clinical setting.

Core

Os Acromiale: Frequency, Anatomy, and Clinical Implications