A Biomechanical and Clinical Comparison of Midshaft Clavicle Fixation Performed With Either Two Or Three Screws On Each Side Of The Plate

OBJECTIVES: Plate fixation with six cortices of purchase (three screws) on each side of the fracture has been the standard of care when operatively treating displaced midshaft clavicle fractures. The use of locking plates and screws may afford equivalent biomechanical strength and clinical outcomes with only four cortices of purchase (two screws) on each side of the fracture. The purpose of this study is to compare the biomechanical and clinical performance of three-screw and two-screw constructs for displaced midshaft clavicle fractures. METHODS: Biomechanical studies employing cantilever bending, deemed most physiologic of midshaft clavicle fracture models, have demonstrated that plate bending and fracture through the end screw hole are the common modes of failure. After simulating midshaft fractures in 10 pairs of embalmed cadaveric clavicles, the biomechanically inferior lateral fragments were randomly assigned to plate fixation with either three non-locking screws or two locking screws. Cyclic tensile loads (10 N to 75 N in a sinusoidal pattern at a rate of 1 Hz) were applied for 5 minutes along the long axis of the clavicle. Then, the constructs were loaded to failure at a rate of 0.5 mm/s with pullout forces applied parallel to the long axis of the screws. Additionally, we retrospectively identified 41 patients who had midshaft clavicle fractures surgically repaired with a minimum follow-up of 6 months: 21 patients were treated with three-screw constructs and 20 patients with two-screw constructs. Patient reported outcomes, radiographic time to union, and complication rates were compared. RESULTS: Biomechanically, there were no significant differences in cyclic displacement (p=0.17), stiffness (p=0.94), yield load (p=0.65), or ultimate load (p=0.622) between the two groups. Clinically, there were no significant differences in American Shoulder and Elbow Surgeons score (ASES) (p=0.35), Constant score (p=0.34), Visual Analog Scale (VAS) pain score (p=0.34), Single Assessment Numeric Evaluation (SANE) score (p=0.99), or average time to union (p=0.74). Complication rates (painful hardware, non-union, hardware failure) trended toward being higher in the three-screw group (p=0.20). CONCLUSION: Plate fixation of displaced midshaft clavicle fractures with four cortices of purchase using two locking screws performs biomechanically and clinically equivalent to fixation with six cortices of purchase using three non-locking screws. Potential beneficial clinical implications include decreased surgical exposure, morbidity, time, and cost. Particularly, with regards to midshaft clavicle fractures, the reduction of the required number of points of cortical fixation from six to four allows the surgeon, in most instances, to use shorter and non contoured straight plates, eliminating the extra time and technical difficulty typically required to fit longer contoured plates to the variable and complex anatomy of the clavicle.