Biomechanical performance of a novel light-curable bone fixation technique

Abstract

Traumatic bone fractures are often debilitating injuries that may require surgical fixation to ensure sufficient healing. Currently, the most frequently used osteosynthesis materials are metal-based; however, in certain cases, such as complex comminuted osteoporotic fractures, they may not provide the best solution due to their rigid and non-customizable nature. In phalanx fractures in particular, metal plates have been shown to induce joint stiffness and soft tissue adhesions. A new osteosynthesis method using a light curable polymer composite has been developed. This method has demonstrated itself to be a versatile solution that can be shaped by surgeons in situ and has been shown to induce no soft tissue adhesions. In this study, the biomechanical performance of AdhFix was compared to conventional metal plates. The osteosyntheses were tested in seven different groups with varying loading modality (bending and torsion), osteotomy gap size, and fixation type and size in a sheep phalanx model. AdhFix demonstrated statistically higher stiffnesses in torsion (64.64 ± 9.27 and 114.08 ± 20.98 Nmm/° vs. 33.88 ± 3.10 Nmm/°) and in reduced fractures in bending (13.70 ± 2.75 Nm/mm vs. 8.69 ± 1.16 Nmm/°), while the metal plates were stiffer in unreduced fractures (7.44 ± 1.75 Nm/mm vs. 2.70 ± 0.72 Nmm/°). The metal plates withstood equivalent or significantly higher torques in torsion (534.28 ± 25.74 Nmm vs. 614.10 ± 118.44 and 414.82 ± 70.98 Nmm) and significantly higher bending moments (19.51 ± 2.24 and 22.72 ± 2.68 Nm vs. 5.38 ± 0.73 and 1.22 ± 0.30 Nm). This study illustrated that the AdhFix platform is a viable, customizable solution that is comparable to the mechanical properties of traditional metal plates within the range of physiological loading values reported in literature.

Figure 1

Workflow for the osteosynthesis of ovine phalanges. (a) Lateral view of an ovine phalanx. (b) Anterior view of an ovine phalanx. (c) Phalanx in 3D printed guide after drilling and cutting. (d) Osteosynthesized phalanx with AdhFix designated for torsion with a narrow patch (Group 5). (e) Osteosynthesized phalanx after PMMA embedding. (f) 3D rendering of osteosynthesized fracture model generated from micro-CT scan.

Figure 2

3D renderings of each testing group. (a) Group 1: AdhFix, four-point bending, 0 mm gap. (b) Group 2: AdhFix, four-point bending, 3 mm gap. (c) Group 3: AdhFix, four-point bending, 0 mm gap. (d) Group 4: Metal plate, four-point bending, 3 mm gap. (e) Group 5: Metal plate, torsion, 3 mm gap. (f) Group 6: AdhFix, torsion, 3 mm gap. (g) Group 7: Metal plate, torsion, 3 mm gap.

Figure 3

Mechanical testing setups. (a) Four-point bending testing setup. The upper contact rollers had a span of 44 mm while the lower contact rollers had a span of 15 mm. The fixture was loaded axially at a rate of 3 mm/min. (b) Torsion testing setup. The lower support was fixed while the upper support was rotated at a rate of 6°/sec. Both supports were 10 mm hexes aligned with the osteosynthesis by a hex cavity in the PMMA embedding.

Figure 4

Box plots and scatter plots of the four-point bending results. Significance is denoted as p < 0.05 = *, p < 0.01 = **, and p < 0.001 = ***. (a) Bending stiffness results. (b) Maximum bending moment results.

Figure 5

Box plots and scatter plots of the torsion results. Significance is denoted as p < 0.05 = *, p < 0.01 = **, and p < 0.001 = ***. (a) Torsional stiffness results. (b) Maximum torque results.

Figure 6

Photos of representative failure modes. (a) Failure of the AdhFix patch across the fracture gap. (b) Failure of the metal construct by catastrophic failure of the phalanx.