UBC Theses and Dissertations
Development of an in vivo device to investigate the effect of mechanical load on allograft remodeling Jamieson, Miranda Lindsay
Failure of a primary hip arthroplasty is often caused by osteolysis which compromises the patient’s periprosthetic bone stock. Impaction allografting involves the use of morselized allograft bone and cement to stabilize the implant and restore this periprosthetic bone stock. Although clinical results of impaction allografting are favourable, regions of necrotic bone graft have been shown to exist for many years post-operatively and may ultimately lead to implant failure. Previous laboratory research has identified a correlation between mechanical stimuli and bone growth; therefore, the purpose of this study was to develop an in vivo device that would enable the investigation of the effect of mechanical load on bone graft incorporation in impacted allograft hip prostheses. An actuator was developed with a finite volume to enable its subcutaneous implantation along the tibia (20mm x 10mm x 10mm) and spine (35mm x 25mm x 15mm) in a rat bone chamber model. The actuator was designed to deliver a dynamic, (1Hz), compressive, (-6N), load that was controlled telemetrically throughout a 6-week long in vivo study. Independent validations of the mechanical actuator and the electrical control system were performed prior to an electromechanical validation of the integrated system. The responsiveness, quantity and magnitude of the load were investigated. The mechanical actuator was motor-driven and the electrical control system was based on radio frequency signal transmission. The electromechanical actuator conformed to the volumetric restrictions of the rat bone chamber model (tibia: 13mm x 17mm x 10mm; spine: 35mm x 30mm x 11mm). A wide range of operating frequencies (0.5 to 3.0 ± 0.05Hz) was achieved and a telemetrically controlled load was produced for 20 seconds per day throughout a simulated 6 week in vivo study. Due to inefficiencies of the mechanical actuator and voltage limitations of the control system, the magnitude of the compressive load produced by the actuator (-1.67 ± 0.10N) was less than specified by the design criteria. Future work to optimize the actuator design and fabrication is warranted in order to increase the maximum load magnitude; however, the current design provides a novel means to begin the investigation of the role of mechanical load on bone graft incorporation in impaction allografting.
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