Bone & Joint Research. 2017 May;6(5):270-6.
Objectives
Fractures of the proximal femur are a common clinical 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, a 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 (X-Bolt), was more torsionally stable, compared to both the dynamic hip screw (DHS, p = 0.008) and helical blade (DHS Blade, p= 0.008) designs in bone
substitute material representative of osteoporotic bone (0.16 g/cm3 polyurethane foam). In
0.08 g/cm3 density substrate, the crucifix design (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 bone substitute material with
density representative of osteoporotic bone. At other densities the torsional stability was
also higher for the X-Bolt, although not consistently significant by statistical analysis.
Cite this article: Bone Joint Res 2017;6:270–276.
Median and IQR for peak torque in 0.16 g/cm3 (pcf 10) and 0.24 g/cm3 (pcf 15) Sawbone.