The normal attachment of the rotator cuff tendons to the bone of the tuberosity is through a complicated transition from flexible tendon, to unmineralized fibrocartilage, to mineralized fibrocartilage to bone (see Assembly, maturation, and degradation of the supraspinatus enthesis)
This gradual transition from flexible bone to stiff tendon allows the insertion to handle the twisting and compression loads it is exposed to throughout its lifetime. Nature’s strategy is the same as that of the electrical plug. It uses a progressive transition between stiff and flexible to minimize wire breakage.
When we attempt to repair a torn rotator cuff, our approximation of the edge of the torn tendon to bone does not re-establish a normal enthesis; thus our repair is inferior to the normal insertion and, as such, vulnerable to failure. “The healing and repair of a degenerated and injured supraspinatus tendon remains a challenge as the original graded tissue of the fibrocartilaginous insert is not recreated after the tendon has been surgically reattached. In the healing area, scar tissue causes mechanically inferior tissue to form.