A device for performing whole bone torsional testing in a single-axis linear motion testing machine

Summary

Objectives: To design a device for the conversion of linear to rotational motion and to use it in order to determine torsional properties of canine tibiae in a universal tension/compression testing machine. Methods: A fixture incorporating a cable and pulley at one end and a guide block and rail assembly at the other was used to test 10 whole canine tibiae to failure in torsion at 1°/s. Results: The device produced spiral fractures in all tibiae. Torsional strength and stiffness were 13.9 ± 1.4 N m and 0.53 ± 0.07 N m/degree, respectively. Clinical significance: This inexpensive device can be used to evaluate the mechanical properties of long bones after various interventions to improve fracture healing. The device can be adapted for use with any single-axis linear motion testing machine. Assessment of fracture healing often includes loading to failure in torsion (1–5). Torsional testing is typically performed using a biaxial servohydraulic testing machine or similar sophisticated electromechanical equipment. Due to its high cost, many researchers do not have such equipment at their disposal. However, uniaxial tension-compression testing machines are widely available. Therefore, a device that can be used to perform torsional testing in a tension-compression machine would be beneficial. In this study we present a custom fixture for converting the vertical linear motion of a universal testing machine to rotational motion and validate its performance in torsional testing of canine tibiae.

Keywords

Torsion - testing fixture - whole bone biomechanics

• References

• 1 Hart MB, Wu JJ, Chao EY. et al. External skeletal fixation of canine tibial osteotomies. Compression compared with no compression. J Bone Joint Surg Am 1985; 67: 598-605.
• 2 Kokubo S, Mochizuki M, Fukushima S. et al. Long-term stability of bone tissues induced by an osteoinductive biomaterial, recombinant human bone morphogenetic protein-2 and a biodegradable carrier. Biomaterials 2004; 25: 1795-1803.
• 3 Amanat N, Brown R, Bilston LE. et al. A single systemic dose of pamidronate improves bone mineral content and accelerates restoration of strength in a rat model of fracture repair. J Orthop Res 2005; 23: 1029-1034.
• 4 Gorman SC, Kraus KH, Keating JH. et al. In vivo axial dynamization of canine tibial fractures using the Securos external skeletal fixation system. Vet Comp Orthop Traumatol 2005; 18: 199-207.
• 5 Tsiridis E, Morgan EF, Bancroft JM. et al. Effects of OP-1 and PTH in anew experimental model for the study of metaphyseal bone healing. J Orthop Res 2007; 25: 1193-1203.
• 6 Taylor D, O’Reilly P, Vallet L. et al. The fatigue strength of compact bone in torsion. J Biomech 2003; 36: 1103-1109.
• 7 Prayson MJ, Datta DK, Marshall MP. Mechanical comparison of endosteal substitution and lateral plate fixation in supracondylar fractures of the femur. J Orthop Trauma 2001; 15: 96-100.