Examining the novel use of continuous compression implants in clavicle reconstruction: A biomechanical study

Current implants for clavicle fractures are known to cause poor cosmesis and irritation, which may require implant removal. Low-profile shape-memory staples provide an attractive alternative, but their biomechanical utility in clavicle reconstruction is unknown. We hypothesized that shape-memory reconstructions would be more compliant compared to traditional constructs but would also outperform conventional plates during cyclic loading to failure.

This study was performed with 36 synthetic clavicles and 12 matched pairs of cadaveric specimens. The synthetic study tested four reconstructions: a single superiorly placed staple (n = 6), a single anteroinferiorly-placed staple (n = 6), a 3.5 mm reconstruction plate (n = 12), and two orthogonally placed staples (n = 12). The cadaveric study tested three constructs: reconstruction plate (n = 8), two orthogonal staples (n = 8), and a 2.7 mm reconstruction plate combined with a superior staple (n = 8). Non-destructive 4-point bending, compression, and torsion assays were performed prior to destructive cantilever bending and cyclic torsion tests.

The single staple and double staple groups demonstrated significantly decreased resistance to bending (p < 0.001) and torsion (p ≤ 0.027) when compared to reconstruction plate groups. The double staple group sustained significantly fewer cycles to failure than the reconstruction plate group in cyclic torsional tests (p = 0.012). The synthetic models produced higher stiffness and failure mechanisms that were completely different from cadaveric specimens.

Shape memory alloy implants provided inadequate stiffness for clavicle fixation but may have utility in other orthopaedic applications when used as a supplementary compression device in conjunction with traditional plated constructs. Synthetic bones have limited capacity for modeling fragility fractures.