Optimal screw orientation for fixation of coronoid fractures.

Objective: The aim of this study was to compare the fixation stability of coronoid fractures achieved by a screw inserted in the anteroposterior (AP) direction with that achieved by a screw inserted in the posteroanterior (PA) direction.

Methods: Eleven pairs of fresh-frozen cadaveric ulna were used. A coronoid fracture was simulated by transverse osteotomy at the midpoint of coronoid height. The specimens of a pair were then randomized to be fixed with an AP screw in one specimen and a PA screw in the other. Insertion torque, load to failure, and stiffness were measured under axial load with a material testing machine.

Results: PA screw placement yielded greater strength and stiffness of fixation than did AP placement. The mean load to failure was 184 N in the PA screw group and 131 N in the AP screw group (P < 0.05). The mean stiffness was 106 N/mm with PA screws and 76 N/mm with AP screws (P < 0.05). These differences were statistically significant despite the fact that the screw insertion torques was similar in PA screw (0.27 Nm) and AP screw (0.25 Nm) (P = 0.2).

Conclusions: PA screw placement was biomechanically superior to AP screw placement. Together with the fact that it is clinically easier to insert and remove screw from the posterior ulna, these data indicate that optimal screw orientation for fixation of coronoid tip fracture is posterior to anterior direction.