Latarjet procedure: biomechanical evaluation of 2-screw coracoid fixation

Abstract

Coracoid nonunion is a relevant complication following the Latarjet procedure and is influenced by multiple factors, including the method of graft fixation. The purpose of this study was to evaluate and characterize the biomechanical properties of various two-screw fixation constructs used for coracoid graft fixation in the Latarjet procedure. Forty model scapulae (Sawbones Inc., Vashon, WA, USA) were used for this study. A 15% anterior inferior glenoid bone defect was created. The coracoid was osteotomized at the juncture of the vertical and horizontal aspects, transferred to the anterior-inferior edge of the glenoid, and fixed with either two 3.5mm fully threaded cannulated cortical screws, two 3.5mm fully threaded solid cortical screws, two 3.5mm partially threaded cannulated screws, or two 4.5mm partially threaded malleolar screws (MS). Biomechanical testing was performed with an Instron material testing machine (Instron Corp., Norwood, MA, USA) by applying loads to the lateral aspect of the transferred coracoid graft. The constructs were preconditioned with nondestructive cyclical loading (0N-20N) to determine construct stiffness. After 100 cycles of dynamic loading, the construct was loaded to failure to determine ultimate failure load, yield displacement, and mode of failure. All failures were associated with plastic deformation of the screws and coracoid graft fracture. There was a significantly lower initial stiffness for partially threaded cannulated screws compared to MS (186±49.3N/mm vs. 280±65.5N/mm, P=.01) but no significant differences among the other constructs. There was no difference in ultimate failure load (P=.18) or yield displacement (P=.05) among constructs. Two screw coracoid fixation of the coracoid in a simulated classic Latarjet procedure with 3.5mm fully threaded cortical and cannulated screws is comparable to 4.5mm MS in strength, stiffness, and displacement at failure. On the other hand, partially threaded 3.5mm cannulated screws provide inferior fixation stiffness and could potentially affect clinical outcomes.