Biomechanical analysis of locked and non-locked plate fixation of the clavicle

During plate fixation of clavicular fractures the brachial plexus and subclavian vessels are vulnerable to injury beneath the clavicle. Locking plate fixation allows for mono-cortical fixation, theoretically reducing the risk of injury to these structures. Biomechanical analysis of the performance of such fixation is limited, and this study was designed to explore this further as a treatment option in clavicle fractures.

Fixation of fifteen simulated mid-shaft fractures was undertaken using a combination of mono-cortical locked, bicortical locked and bicortical non-locked plating methods in cadaveric clavicles. Samples were then tested via three-point bending to destruction, and the performance of each with respect to failure load, bending stress, bending stiffness and Young's modulus was then analysed. The influence of the number of cortices engaged and locking was also assessed.

Clavicles fixed with monocortical locking plates displayed a significantly lower bending stress (12±1 MPa) than both the bicortical locking (28±3 MPa, p=0.015) and non-locking specimens (24±3 MPa, p=0.002). Engaging two cortices with the fixation produced a significant increase in failure load (291±28 N vs 138±48 N, p=0.018) and bending stress (26±2 MPa vs 9.9±3.5 MPa, p=0.002) compared to single cortex fixation.

The greatest influence upon the performance of the fixation was the number of cortices engaged, with bicortical fixation performing significantly better than mono-cortical. Whether or not the fixation device was a locking one did not have a significant bearing upon the performance.

This in vitro biomechanical analysis demonstrates that mono-cortical locked plating fails at significantly lower levels of load and stress than bicortical locked and non-locked plating in mid-shaft fractures of the clavicle, and caution would therefore be advised in its use as a fixation modality for these injuries.