Fluoroscopic comparison of kinematic patterns in massive rotator cuff tears. A suspension bridge model.

Twelve shoulders with known massive rotator cuff tears were imaged fluoroscopically. The observed kinematic patterns were correlated with the known locations of the rotator cuff tears. Three kinematic patterns emerged: Type I, stable fulcrum kinematics associated with tears of the superior rotator cuff (supraspinatus and a portion of the infraspinatus); Type II, unstable fulcrum kinematics associated with tears that involved virtually all of the superior and posterior rotator cuff; and Type III, captured fulcrum kinematics associated with massive tears that involved the supraspinatus, a major portion of the posterior rotator cuff, and a major portion of the subscapularis. In Type III, an "awning effect" of the acromion was observed to influence active motion. Based on the recorded kinematic patterns, a biomechanical model was developed comparing the rotator cuff tear to a suspension bridge (loaded cable). A biomechanical analysis of forces acting on the rotator cuff according to this model yielded data that supported the contention that certain rotator cuff tears in older individuals may be adequately treated with debridement and decompression, without repair.