[Anatomical study on the atrophy of supraspinatus muscle belly with cuff tear]

We dissected the 76 shoulders in 38 cadavers to investigate changes in the supraspinatus muscle with a cuff tear and correlated these with age. We made a transverse section in the supraspinatus muscle and stained the section by the van Gieson method. Then we analyzed the changes in the supraspinatus muscle belly with the cuff tear, and by age, measuring the short and long diameter of a slice of the muscle belly and the area of tendon fiber. In the group with a normal cuff, there was a negative correlation between age and the short diameter of the slice of the supraspinatus muscle but no significant correlation between the age and the long diameter of the slice. In the group with a cuff tear, not only the short diameter but also the long diameter of the slice of the supraspinatus muscle decreased with increase in the length of the cuff defect. We concluded that measuring the long diameter of the slice of the supraspinatus muscle was more efficient than measuring the short diameter to evaluate muscle atrophy with a cuff tear. The area of the tendon in the slice increased with the length of cuff defect. The increased area of the tendon may have been responsible for reducing the elasticity in the supraspinatus muscle with a cuff tear.