The Effect of Screw Design and Cortical Augmentation on Insertional Torque and Compression in Coracoid-Glenoid Fixation in a Sawbones Model

Abstract

To compare screw insertional torque and coracoid-glenoid compression from 4 fixation techniques with different screw design parameters and cortical augmentation for the Latarjet procedure. Simulated Latarjet procedures were performed with 4 fixation techniques using laminated polyurethane blocks with dimensions similar to the coracoid-glenoid construct. The groups included DePuy Synthes Mitek 3.5-mm partially threaded screws with top hats, Arthrex 3.75-mm fully threaded screws with a 2-hole plate, Arthrex 3.75-mm fully threaded screws, and Smith & Nephew 4.0-mm partially threaded screws. Screws were inserted using a digital torque-measuring screwdriver to determine maximum insertional torque. Pressure-sensitive film was used to measure the maximum contact pressure and the effective pressure distribution (EPD) between the coracoid and glenoid; the EPD represents the percentage of the film's surface area that experienced pressure greater than 10 MPa. One-way analysis of variance and post hoc tests were used for statistical analysis. Significant differences were found between the 4 fixation groups for each variable measured. The 2 cortically augmented systems produced significantly higher maximum insertional torque than the non-cortically augmented systems (P < .001 for both). The 3.75-mm screws with a 2-hole plate yielded significantly higher contact pressures than the 4.0-mm screws (P= .028). This group also had a high EPD, with a mean value more than double the values of the non-cortically augmented systems (P= .037 and P < .001). Cortically augmented fixation methods showed higher maximum insertional torque, maximum contact pressure, and EPD between the surfaces of the coracoid and glenoid in this Sawbones model. Various implants are available for the Latarjet procedure, but their biomechanical characteristics have not yet been fully elucidated. Graft fracture and nonunion represent 2 modes of failure that may be related to insertional torque and coracoid-glenoid compression. This study compared screw insertional torque and compression achieved using 4 fixation techniques with different screw design parameters and cortical augmentation in a Sawbones model.