Simulation of postoperative scapula fractures after rTSA

Reverse total shoulder arthroplasty (rTSA) is recommended in case of severe muscle deficiency, along with important joint wear. Although having a correct placement of the prosthesis after the operation and a recovery of the mobility, several cases of scapula fracture are reported, in the region of the scapular spine or the acromion. Complication occurs 3 to 9 months after the surgery and may necessitate a second intervention. Such fractures are likely to be provoked by important stresses in the scapula, due to the change in joint configuration. A 3D numerical model of the shoulder, including the prosthesis, was developed with Abaqus CAE to investigate the stresses in the different regions of the joint, when performing an abduction movement with the arm. The aim of the project is therefore to adapt the model to some known problematic cases, in order to identify the cause of fracture and identify the important parameters. This project focuses on simulating the forces to determine the stresses that appear in the scapula. For this, data from CT scans was used to model the shoulders of several patients including the prosthesis and deltoid muscle. The four cases analyzed were a healthy cadaver's scapula, a case of successful rTSA, and two fracture cases. Then the data was analyzed, to identify the impact of the prosthesis and that of the muscle, and determine whether it is possible to predict a fracture. It was found that the stress values are higher for the two scapulae, which is a sign that there is a fracture risk. Also, the maximum stress areas are close to the fracture areas in the two fracture cases, thus mechanically weak spots can be identified preoperatively and fractures anticipated. This is a promising technique, but would require more work and validation.