Fatty degeneration in the supraspinatus muscle after rotator cuff tear.

We studied the relationship between fatty degeneration in the supraspinatus muscle after rotator cuff tear and muscle atrophy and tendon retraction in 41 cadaveric shoulders. Eighteen shoulders had a supraspinatus tendon tear. Transverse sections of the supraspinatus muscle were made at the proximal end of the scapular notch. The tendon fiber areas were stained red and the muscle fiber areas were stained yellow by the van Gieson method. Areas of fatty degeneration were stained orange-red by the Sudan three method. These areas were measured with a computer color image analysis system. There were many areas of the fatty degenerative change in the supraspinatus muscles associated with a cuff tear, mainly around the tendon fibers and the vessels. The fatty degeneration in the supraspinatus muscle after cuff tear was found to have a strong association with the degree of retraction of the tendon fibers rather than the reduction of muscle volume.