Biomechanical analysis of bicortical versus unicortical locked plating of mid-clavicular fractures

Abstract

Operative fixation of displaced mid-shaft clavicle fractures has been shown to improve the functional outcomes and decrease the likelihood of non-union; however, little is known about the need for locking screws versus traditional screws. We, therefore, evaluated the strength of unicortical locked plating versus traditional bicortical non-locking fixation methods. Ten matched pairs of fresh, frozen cadaver clavicle specimens were obliquely osteotomized through the mid-shaft to represent the most common fracture pattern. After randomization, the clavicles were repaired using pre-contoured plates with either standard bicortical non-locking screws or unicortical locking screws. The constructs were then potted in cement and tested on a MTS machine using a custom gimble and evaluated for load to failure and axial and rotational stiffness. There was no significant difference between the constructs in terms of axial stiffness (locking 688.3 ± 306.2 N/mm, non-locking 674.5 ± 613.0 N/mm; p = 0.77) or load to failure (locking 720.1 ± 232.0 N, non-locking 664.8 ± 167.5 N; p = 0.46). However, rotational stiffness varied significantly (locking 1.70 ± 0.91 N-m/mm, non-locking 2.49 ± 0.78 N-m/mm, p = 0.049) with bicortical non-locking constructs exhibiting higher torque values. Unicortical fixation using pre-contoured plates and locking screws has a similar biomechanical profile compared to gold standard non-locked bicortical screws in cyclic axial compression and axial load to failure. Non-locking constructs were stiffer under rotational testing. This technique may provide a suitable biomechanical environment for bony healing. This may also improve the safety of clavicle plating by protecting infraclavicular structures from injury during drilling or screw penetration as it obviates the need for bicortical fixation.