The efficacy of rotational control designs in promoting torsional stability of hip fracture fixation

Abstract
Objectives: Proximal fractures of the femur are a common problem, and a number of orthopaedic devices are available for the treatment of such fractures. The objective of this study was to assess the rotational stability, a common failure predictor, of three different rotational control design philosophies, a screw, helical blade and a deployable crucifix.
Methods: Devices were compared in terms of the mechanical work (W) required to rotate the implant by 6° in a bone substitute material. The substitute material used was Sawbones polyurethane foam of three different densities (0.08 g/cm3, 0.16 g/cm3 and 0.24 g/cm3). Each torsion test comprised a steady ramp of 1°/minute up to an angular displacement of 10°.
Results: The deployable crucifix design (the X-Bolt), was more torsionally stable, compared to both the screw (DHS, p = 0.008) and helical blade (DHS Blade, p= 0.008) designs in osteoporotic bone substitute material (0.16 g/cm3 polyurethane foam). In 0.08 g/cm3 density substrate, the crucifix design (the X-Bolt) had a higher resistance to torsion than the screw (DHS, p = 0.008). There were no significant differences (p = 0.101) between the implants in 0.24 g/cm3 density bone substitute.
Conclusions: Our findings indicate that the clinical standard proximal fracture fixator design, the screw (DHS), was the least effective at resisting torsional load, and a novel crucifix design (X-Bolt), was the most effective design in resisting torsional load in osteoporotic bone substitute material. At other densities the torsional stability was also higher for the bolt, although not always statistically significant.