Comparison of a novel surgical implant with the volar locking plate for the treatment of distal radius fractures: a mechanical study

Abstract

Distal radius fractures are the most common osteoporotic fractures among women. The treatment of these fractures has been shifting from a traditional non-operative approach to surgery, using volar locking plate (VLP) technology. Surgery, however, is not without risk, complications including failure to restore an anatomic reduction, fracture re-displacement (loss of reduction), and tendon rupture. The objectives of this study were to optimize the design of a novel surgical implant and compare it to the gold-standard VLP, in terms of mechanical stability (assessed by mechanical testing) and long-term effects (assessed by computer simulation). The implant is novel in a variety of ways. Rather than being an externally applied device, its application is as an intramedullary device designed to fill the distal radial metaphysis to the extent that it stabilizes the fracture. It consists of two elements: rods and spheres. In this research, various design iterations for rods were prototyped and tested on cadaveric specimens to obtain a balance between different number/types of rods, stability and technical ease. A combination of radial and volar rods linked together proximally was found to best meet the criteria. Ideally, the spheres should be porous to accommodate bone in-growth. A design optimization study was performed to find the optimal balance between porosity and load carrying capacity. The results showed perforated spheres have the potential to be primarily used. To compare the long-term effects of this implant and VLP, a subject-specific finite element model of the radius, integrated with a bone adaptation algorithm, was constructed. The final density distributions of the two implants were compared together as a predictor of the stress shielding damages. Our results showed that the novel implant appeared to lead to higher density distribution. To evaluate the mechanical stability, a custom passive wrist joint simulator was designed and built. A ten-millimeter defect (experimental fracture) in the dorsal cortex of the distal radius was created in seven cadaveric specimens. In sequence the distal radius was first stabilized with the new intramedullary device, and then with a VLP. Resistance to cyclic fatigue loading was evaluated for each treatment method by measuring the change of fracture-length during testing. On average, the change in fracture-length for the novel implant and VLP were 1.34 and 0.10 mm, respectively. In conclusion, this study showed potential of the presented novel implant. It was demonstrated that the novel implant provides better biocompatibility than the VLP and has the potential to maintain near complete fracture stabilization. Further research, however, is needed to refine the surgical technique in order to achieve fracture stability.