In vitro biomechanical comparison of the effects of cerclage wires, an intramedullary pin and the combination thereof on an oblique osteotomy of the canine tibia.

OBJECTIVE

To compare the in vitro biomechanical effects of single loop cerclage wires, an intramedullary pin and the combination thereof as applied to an oblique mid-diaphyseal osteotomy of canine tibiae.

METHODS

Three groups of nine bones with long oblique osteotomies were repaired with the following methods: 1) Three single loop cerclage wires and a transcortical skewer pin, 2) intramedullary pinning with a smooth Steinmann pin, and 3) a combination of both methods. The repaired constructs were tested in a single cycle four-point-bending test to failure. Load displacement curves were drawn and the following parameters were calculated or extrapolated: Stiffness, load at yield, and force resisted at 2 mm actuator displacement. The latter was determined to demonstrate the difference in the amount of energy absorbed between the different groups.

RESULTS

The stiffness and force resisted at 2 mm displacement of the groups with cerclage wires were significantly higher than the group with an intramedullary pin alone (p ≤0.05). The differences in stiffness (p = 0.15) and force required at 2 mm displacement (p = 0.56) between cerclage wires and the combination of cerclage wires and intramedullary pins were not significant.

CLINICAL RELEVANCE

Cerclage wire repair results in higher stiffness than repair with an intramedullary pin. When cerclage wires are combined with an intramedullary pin, the intramedullary pin does not provide protection to the cerclage wire repair and the wires or the bone under the wires has to fail before the pin resists significant load.