Abstract
Periprosthetic bone loss following orthopedic implantations is a serious concern leading to the premature failure of the implants. Therefore, investigating bone remodeling in response to orthopedic implantations is of paramount importance for the purpose of designing long lasting prostheses. In this study, a predictive bone remodeling model (Thermodynamic-based model) was employed to simulate the long-term response of femoral density to total hip arthroplasty (THA), bone fracture plating and intramedullary (IM) nailing. The ability of the model in considering the coupling effect between mechanical loading and bone biochemistry is its unique characteristic. This research provided quantitative data for monitoring bone density changes throughout the femoral bone. The results obtained by the thermodynamic-based model agreed well with the bone morphology and the literature. The study revealed that the most significant periprosthetic bone loss in response to THA occurred in calcar region (Gruen zone 7). Conversely, the region beneath the hip stem (Gruen zone 4) experienced the lowest bone mineral density (BMD) changes. It was found that the composite hip implant and IM nail were more advantageous over the metallic ones as they induced less stress shielding and provided more uniform bone density changes following the surgery. The research study also showed that, due to plating, the areas beneath the bone fracture plate experienced severe bone loss. However, some level of bone formation was observed at the vicinity of the most proximal and distal screw holes in both lateral and anterior plated femurs. Furthermore, in terms of long-term density distributions, the anterior plating was not superior to the lateral plating.
Highlights
In order to validate the simulations against clinical studies, the results were compared to the study by Li et al [25] who measured the periprosthetic changes in bone mineral density (BMD) in response to total hip arthroplasty (THA) using dual energy X-ray absorptiometry (DEXA). [25] reported that 2 years after THA with a CoCr implant, the maximum bone loss occurs in zone 7 with a percent change of -19.7% which is consistent with our results
This small deviation implies that the femur implanted with the composite hip implant is not subjected to excessive stress concentration, is under a lower risk of fracture, which can be counted as another privilege of carbon fiber (CF)/PA12 implant
A mechano-biochemical model, which considers the coupling between the mechanical loading and biochemical affinity as stimulus for bone remodeling, was employed in this study to simulate the long-term behaviour of the femur in response to total hip arthroplasty, plating and intramedullary nailing
Summary
Artificial joint prostheses and fracture fixation devices are implanted in patients with diseased or damaged joints or fractured bones to lessen pain and restore the appropriate function. Metallic implants including hip implants and fracture fixation devices are much stiffer than bone, and carry a high amount of load compared to bone Due to this abnormal load sharing, the bone around the implant is stress shielded which leads to bone loss, painful implant loosening and failure eventually. It is important to develop and use mathematical models to predict bone remodeling and monitor the evolution of bone density after implantations to identify the risk of periprosthetic bone loss and improve the overall design of implants. To this end, many models have been developed, so far [1-5]. In the current study, a mechano-biochemical bone remodeling model (thermodynamicbased model developed by [6] and modified by [7, 8]) was employed which links the mechanical factors to biological ones, to more realistically predict bone density changes in response to orthopedic implantations
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