OBJECTIVE: To explore the MRI findings of os acromiale and to analyze the relationship between os acromiale and the supraspinatus and infraspinatus injury. METHODS: From January 2010 to August 2020, 21 patients with os acromiale (os arcomiale group) were compared with 21 subjects with no evidence of os acromiale (no os arcomiale group). There were 14 males and 7 females in the os arcomiate group, aged from 29 to 77 years old, mean aged (55.5±11.5) years old. While in the control group, there were 10 males and 11 females in no os arcomiale group, aged from 31 to 70 years old, mean aged (51.1±10.0) years old. The os acromiales were classified as edematous os acromiale or non-edematous os acromiale based on whether the presence of marrow edema, and as displaced os acromiale or non-displaced os acromiale based on whether the presence of displacement of the os acromiale. The MRI features of os acromiale were analyzed. Statistical analyses were performed to identify the differences between the os arcomiale group and no os arcomiale group regarding rotator cuff tear, supraspinatus and infraspinatus injury. Differences in the supraspinatus and infraspinatus tear between the edematous and non-edematous os acromiale group, the displaced and non-displaced os acromiale group, the displaced os acromiale and no os arcomiale group were also assessed. RESULTS: On MRI, all the 21 os acromiales appeared as a triangular or irregular bone fragment of the distal acromion, and forms a pseudo-acromioclavicular joint with the acromion. Eleven cases were edematous os acromiale, 11 cases were displaced os acromiale. In the os arcomiale group, 17 had supraspinatus tear, 1 had supraspinatus tendinitis, 11 had infraspinatus tear, and 4 had infraspinatus tendinitis. In the no os arcomiale group, 11 had supraspinatus tear, 2 had supraspinatus tendinitis, 5 had infraspinatus tear, and 1 had infraspinatus tendinitis. No statistically significant difference between the os arcomiale group and no os arcomiale group regarding the rotator cuff tear, supraspinatus and infraspinatus injury (P>0.05). In the 11 cases of edematous os arcomiale, 10 had supraspinatus tear and 7 had infraspinatus tear. In the 10 cases of non-edematous os acromiale, 7 had supraspinatus tear and 4 had infraspinatus tear. No statistically significant difference was noted between the edematous os acromiale and non-edematous os acromiale in terms of supraspinatus and infraspinatus tear (P>0.05). In the 11 cases of displaced os acromiale, 11 had supraspinatus tear and 9 had infraspinatus tear. In the 10 cases of non-displaced os acromiale, 6 had supraspinatus tear and 2 had infraspinatus tear. In the no os arcomiale group, 11 had supraspinatus tear and 5 had infraspinatus tear. There was a statistically significant increases in the prevalence of supraspinatus and infraspinatus tear in the displaced os acromiale group compared with non-displaced os acromiale group, the displaced os acromiale group and no os arcomiale group(P<0.05). CONCLUSION Shoulder MRI can very well depict os acromiale and can reveal associated abnormalities such as adjacent bone marrow edema, displaced deformity, and rotator cuff tear, and it can be used to assess the stability of the os acromiale. The presence of os acromiale may not increase the risk of supraspinatus and infraspinatus tear significantly. However, the presence of displaced os acromiale is at greater risk of supraspinatus and infraspinatus tear.
Acromion/diagnostic imaging* ; Adult ; Aged ; Female ; Humans ; Magnetic Resonance Imaging ; Male ; Middle Aged ; Rotator Cuff ; Rotator Cuff Injuries/diagnostic imaging* ; Shoulder