Comparison of two coracoid process transfer techniques on stress shielding using three-dimensional finite-element model

Background We created patient-based 3D finite-element (FE) models that simulate the congruent-arc Latarjet (CAL) and traditional Latarjet (TL) procedures and then compared their stress distribution patterns with different arm positions and glenoid defects. Methods The computed tomography data of 10 adult patients (9 men and 1 woman, ages: 18-50 years) were used to develop the 3D FE glenohumeral joint models. Twenty-five and 35% bony defects were created on the anterior glenoid rim, and the coracoid process was transferred flush with the glenoid by the traditional and congruent-arc techniques using two half-threaded screws. A load was applied to the greater tuberosity toward the center of the glenoid, and a tensile force (20 N) was applied to the coracoid tip along the direction of the conjoint tendon. The distribution patterns of the von Mises stress in the traditional and congruent-arc Latarjet techniques were compared. Results The mean von Mises on the graft was significantly greater for the TL technique than for the CAL. While the von Mises stress was greater in the distal medial part of the graft in the TL models, a higher stress concentration was observed in the distal lateral edge of the coracoid graft in the CAL models. The proximal medial part of the graft exhibited significantly lower von Mises stress than the distal medial part when compared according to technique, defect size, and arm position. Increasing the glenoid defect from 25 to 35% resulted in a significant increase in stress on the lateral side of the graft in both models. Conclusion The stress distribution patterns and stress magnitude of the coracoid grafts differed according to the procedure. Due to placing less stress on the proximal-medial part of the graft, the CAL technique may lead to insufficient stimulation for bone formation at the graft-glenoid interface, resulting in a higher incidence of graft osteolysis. Clinical relevance The CAL technique may lead to a higher incidence of graft osteolysis.