We created each surface and deep rotator cuff tear model using fresh-frozen cadavers to quantitatively measure the strain on the surface layer and deep layer of the supraspinatus tendon due to continuous increase in tension on the supraspinatus tendon. Next compared the strain between non-tear status and remaining tendon of the partial-tear status.
20 fresh-frozen shoulder specimens from 20 cadavers were utilized (10 surface tear model, 10 deep tear model). The shoulders were fixed at an angle ranging from each -10 to 30 degrees on the scapular plane, and the tensile load on the supraspinatus tendon was increased from 0 to 120 N. A strain gauge was installed in the surface or deep layer of the supraspinatus tendon and measured as the non-tear status. Next surface or deep layer was cut, and remaining tendon layer was measured again.
Significant increases in the strain on the deep layer of the supraspinatus tendon were observed with increases in the tensile force on the supraspinatus tendon. The strain of the surface layer of the supraspinatus tendon was significantly larger at -10 to 0 degrees, whereas the deep layer was significantly larger at 20 to 30 degrees. At all scapula elevation angles, the strain on the surface and deep layer of the supraspinatus tendon increased in the partial tear status in comparison to the non-tear. Strain of the surface layer of the supraspinatus tendon under the maximum tensile force of 120 N was 3.33 % (deep-tear) vs. 3.04 % (non-tear) at a scapular plane elevation of -10 and 0 degrees, and deep layer was 6.35 % (surface-tear) vs. 3.26 % (non-tear) at a scapular plane elevation of 30 degree.
In our previous study, we reported that the strain on the surface and deep layer of the supraspinatus tendon at a scapular plane elevation from -10 to 30 degrees. In this study, strain of the surface layer of the supraspinatus tendon wasn’t large. However, strain of the deep layer of the supraspinatus in surface tear was approximately twice as large as those in the non-tear. For this reason, surface tears are considered to have a higher risk of tear expansion by tensile force on the remaining tendon.
This finding can be applied to the provision of safer and more effective shoulder physical therapy in clinical and sports settings for patients with known or suspected partial tendon tears.
partial rotator cuff tear
remaining tendon strain
