A New Method of Contact Stress Measurement for Analyzing Internal Impingement Syndrome of the Shoulder: Potentials and Preliminary Evaluation

Shoulder impingement syndrome causes critical disorders such as rotator cuff tear or superior labrum anterior to posterior (SLAP) lesion in both the general public and in athletes whose sports involve throwing. Nevertheless, the biomechanics of the syndrome still have not been clarified. Contact stress measurement in vivo during shoulder motion is essential to identifying the biomechanics of the syndrome. There have been no reports to date regarding internal impingement syndrome among the syndrome studied by using the finite element method (FEM). The proposed method simulates the internal impingement syndrome according to shoulder motion using the FEM. The method solves the critical process zone error at the supraspinatus tendon insertion according to impingement of the 3D biomechanical model by relaxing the boundary condition for representation of shoulder motion. The simulation results confirmed that the proposed method allowed for the analysis of internal impingement syndrome by measuring contact stress (23.13 MPa) during shoulder motion. The performance of the proposed method was examined through the differential displacement (maximum 3.28 mm) in shoulder motion by boundary condition relaxation. The result of the simulation was consistent with the clinical findings.