Military personnel with amputations face unique challenges due to their short residual limbs and high incidences of multiple limb loss sustained after blast injuries. However, transcutaneous osseointegrated implant (TOI) technology may provide an alternative for individuals with poor socket tolerance by allowing a structural and functional connection between living bone and the surface of a load bearing implant. While TOI has improved activity levels in European patients with limb loss, a lengthy rehabilitation period has limited the expansion of this technology, and may be accelerated with electrical stimulation. The unique advantage of electrically induced TOI is that the exposed exoprosthetic attachment may function as a cathode for regulating electrical current while also serving as the means of prosthetic limb attachment to the host bone. Using this design principle, the goal of this dissertation was to investigate the potential of electrical stimulation for enhancing the rate and magnitude of skeletal fixation at the periprosthetic interface using the implant as a cathode.
Although previous studies have examined electrical stimulation for healing atrophic nonunions, inconsistent results have required new predictive measures. Therefore, finite element analysis (FEA) was used as a prerequisite for estimating electric field and current density magnitudes prior to in vivo experimentation. Retrospective computed tomography scans from 11 service members (28.3 ± 5.0 years) demonstrated the feasibility of electrically induced TOI, but variability in residual limb anatomy and the presence of heterotopic ossification confirmed the necessity for patient-specific modeling.
Electrically induced osseointegration was also evaluated in vivo in skeletally mature rabbits after establishing design principles based on in vitro cell culturing and FEA. Data from the animal experiment indicated that there were no statistical differences for the appositional bone index (ABI), mineral apposition rate and porosity between the electrically stimulated implants and the unstimulated control implants (UCI). Higher mechanical push-out forces were observed for the UCI group at 6 weeks (p=0.034). In some cases, qualitative backscattered electron images and ABI did indicate that direct current may hold promise for improving suboptimal implant “fit and fill,” as bone ongrowth around the cathode was observed despite not having direct contact with the endosteum.
|1988||Carter DR, Blenman PR, Beaupré GS. Correlations between mechanical stress history and tissue differentiation in initial fracture healing. J Orthop Res. September 1988;6(5):736-748.|
|1957||Fukada E, Yasuda I. On the piezoelectric effect of bone. J Phys Soc Jpn. October 1957;12(10):1158-1162.|
|1980||Martin RB, Pickett JC, Zinaich S. Studies of skeletal remodeling in aging men. Clin Orthop Relat Res. June 1980;149:268-282.|
|2007||Skedros JG, Baucomb SL. Mathematical analysis of trabecular "trajectories" in apparent trajectorial structures: the unfortunate historical emphasis on the human proximal femur. J Theo Biol. January 7, 2007;244(1):15-45.|
|1979||Currey JD. Changes in the impact energy absorption of bone with age. J Biomech. 1979;12(6):459-469.|
|1974||Reilly DT, Burstein AH. The mechanical properties of cortical bone. J Bone Joint Surg. 1974;56A(5):1001-1022.|
|2006||Nyman JS, Roy A, Shen X, Acuna RL, Tyler JH, Wang X. The influence of water removal on the strength and toughness of cortical bone. J Biomech. 2006;39(5):931-938.|
|1970||Currey JD. The mechanical properties of bone. Clin Orthop Relat Res. November–December 1970;73:210-231.|