Transcutaneous osseointegrated implants (TOI) have been shown to improve functionality for patients with limb loss by allowing direct skeletal attachment between an exoprosthesis and host bone. However, a lengthy rehabilitation period has limited the expansion of TOI and may be accelerated with electrical stimulation. The purpose of this study was to determine the ability of direct current (DC) cathode stimulation to enhance osseointegration of intramedullary implants in skeletally matured rabbits. Bilateral implants were inserted in the hind limbs of 25 adult female rabbits. The left hind limb of each animal was continually stimulated with a potential difference of 0.55 volts based on finite element analysis predictions. After sacrifice, the limbs were divided into two groups: Group I for histology and Group II for biomechanical testing. The bone-implant construct was evaluated in the Group I animals using appositional bone index (ABI), mineral apposition rates (MAR), histological staining, and scanning electron microscopy (SEM). Group II implants were sectioned and subjected to mechanical push-out tests. Data indicated no statistical differences for ABI, MAR, and porosity between the electrically stimulated implants (ESI) and the unstimulated control implants (UCI) at three weeks and six weeks. Higher mechanical push-out forces were observed in the UCI group at six weeks (p = 0.034). Data indicated that DC cathode stimulation may improve suboptimal implant "fit and fill" as an increase in trabecular bone was noted around the cathode in the ESI group. However, longer time duration animal studies and variations in electrical modalities may be required before electrically induced osseointegration becomes clinically feasible.
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