First metatarsophalangeal joint arthrodesis is a common procedure for the treatment of hallux rigidus, severe or recurrent bunion deformities, failed hallux valgus, chronic inflammatory and neuromuscular conditions or trauma. With each step in gait, the first MTP joint is stressed by up to 90% of body weight, while loading of the metatarsal head and base during each foot push-up can reach up to 29% of body weight. To withstand these high mechanical forces, a successful fusion is dependent on joint preparation and rigid fixation. In this study, we used a finite element analysis, FEA, to assess a novel biointegrative fiber reinforced screw and nail construct. This biointegrative technology may provide improved mechanical fixation profile through its high flexural strength and flexural modulus closely matching cortical bone. Materials and methods. The first MTP joint of an adult male, weighing 80 kilograms, was segmented from a left foot CT scan and meshed to finite elements and incorporated a three-dimensional CAD model. Biointegrative fiber reinforced 4-0 partially threaded headless compression screws and a three millimeter fiber reinforced cannulated nail from Osseo Limited were inserted into this computational model in a crossed fashion. The biointegrative implants are composed of continuous reinforcing mineral fibers comprised of elements found in native bone and bound together by a degradable polymer. Two 4-0 partially threaded headless titanium screws were inserted in a similar trajectory in a separate model and served as the control. The finite element analysis algorithm was based on published known forces acting on the first ray during push-off. Post-processing was performed on FEA results and the models were simulated to evaluate the mechanical strength and stress concentrations acting on the surrounding cortical bone following the use of the biointegrative implants compared to conventional metal fixation. The relative displacement between the metatarsal and phalangeal heads upon simulated loading was 1.6 millimeters for metal fixation and 0.2 millimeters for the biointegrative fixation, demonstrating this technology to be mechanically stable at least as conventional metal fixation. In both models, the von Mises maximum stresses were found between the implant thread and shank, however, maximal localized stresses in cortical bone regions interacting with the metal implants were substantially higher, up to eight times, compared to the biointegrative implant bone interactions. Moreover, stresses in the implant body were remarkably higher with the metal implants compared to the biointegrative fixation. These results indicate that for physiological loading, conditions applied in the first MTP for this situation, the use of biointegrative fixation may reduce stress concentrations at the implant cortical bone interface. Discussion. These FEA results indicate that biointegrative screw nail constructs provide equivalent mechanical fixation strength to metal fixation while resulting in lower bone implant stress concentrations. The flexural modulus of the biointegrative material closely matching that of cortical bone decreases implant bone resistance level and the probability of bone implant failure and risk for implant loosening, all common complications in foot and ankle surgery. This study demonstrates a new methodology for CT-based finite elemental analysis for the evaluation of the first MTP joint fusion arthrodesis and suggests the biointegrative screw nail combination as an alternative to additional metal fixation. There are plans to implement this on a clinical basis following the following construct. In figure five, you can see the nail and its radio opaque K wire being inserted with its screwdriver. The second picture demonstrating a postoperative x-ray and the same patient, 13 weeks following successful first MTP joint arthrodesis. Thank you very much.

biointegrative fiber reinforced screw

nail construct

first metatarsophalangeal joint arthrodesis

hallux rigidus

bunion deformities