Biomechanical Analysis of the Fixation Strength of a Novel Plate for Greater Tuberosity Fractures

BACKGROUND: The incidence of isolated greater tuberosity fractures has been estimated to be 20% of all proximal humeral fractures. It is generally accepted that displaced (>5 mm) fractures should be treated surgically but the optimal surgical fixation of greater tuberosity fractures remains unclear. OBJECTIVE: The goal of this study was to simulate the environment of application of a new plate system (Kaisidis plate, Fa Königsee) for fractures of greater tuberosity, and to demonstrate the stability of the plate. METHODS: A Finite Element Method (FEM) simulation analysis was performed on a Kaisidis plate fixed with nine screws, in a greater tuberosity fracture model. Solid Works 2015 simulation software was used for the analysis. The Kaisidis plate is a bone plate intended for greater tuberosity fractures. It is a low profile plate with nine holes for 2,4 mm diameter locking screws, eight suture holes and additional K-wire holes for temporary fixation of the fragment. The supraspinatus tendon has the greatest effect on the fracture zone, and as such, was the primary focus for this study. For this study, we performed only linear calculations. RESULTS: The calculations were performed in a way so that the total applied force resulted in a maximum stress of 816 N/mm(2). The findings indicated that the most critical points of the Kaisidis system are the screws that are connected to the bone. The maximal force generated by the supraspinatus tendon was 784 N, which is higher than the minimal acceptable force. The results of the FEM analysis showed that the maximal supraspinatus force was 11.6% higher than the minimal acceptable force. As such, the load would exceed twice the amount of maximal force required to tear the supraspinatus tendon, before the screw or the plate would show first signs of plastic deformation. CONCLUSION: Based on the results of this analysis and the fulfilment of our acceptance criterion, the FEM model indicated that the strength of the Kaisidis plate exceeded that of the proposed maximum loads under non-cycli loading conditions.