The average life expectancy of many people undergoing total hip replacement

The average life expectancy of many people undergoing total hip replacement (THR) exceeds twenty-five years and the demand for implants that increase the load-bearing capability of the bone without affecting the short- or long-term stability of the prosthesis is high. hip prostheses fail to function properly due to the loosening of the fixations after long-term use [3, 4]; debonding of the cement-stem and cement-bone interfaces and the local fractures in the cement mantle were perceived as the primary mechanisms of cemented hip implant loosening [4]. Improved cementing techniques had then been developed to reduce the prevalence of loosening and to guarantee long-term fixation of the prosthesis [5C9]. Stress shielding of the bone received increased attention over the years [10]; whether cemented or uncemented implants were used, mechanical loosening owing to the physiological dynamic response of the bone is one of the main factors affecting the implants long-term durability. The presence of the femoral implant in the intramedullary canal reduces the loads normally applied to the bone of the proximal femur, resulting in periprosthetic bone resorption, bone loss, cortical bone thinning, and joint prosthesis failure [11C15]. Revision surgery to address such failure involves increased risks, complications, and costs. Given that the average life expectancy of many patients undergoing total hip arthroplasty (THA) exceeds 25 years, ongoing stress shielding is clinically important and the demand for implants which maximize the load-bearing capabilities of the bone is high [16, 17]. Implant design and material properties have great effects on the total hip joint stability and long-term performance. For instance, if the stem design and material lead to high stresses in the fixation area of the prosthesis, local fractures or fatigue failure of the cement is quite likely to occur. Observations from fatigue experiments and clinical studies had attributed the loosening of the cement-stem fixation to the local fractures initiated in the cement mantle adjacent to the stem that gradually propagated and produced separation of the stem-cement interfaces [4, 18, 19]. Concurrent with cement damage and stress shielding other studies revealed that stiffer implants induce high levels of stress shielding over the proximal femur and low levels of interface stress among the femur-implant constituents [20, 21], while Rabbit polyclonal to MMP1 in contrast less stress shielding and high levels of cement damage were observed with low stiffness implants [22]. The long-term survival of the cemented prosthesis is contingent on achieving a balance between stress shielding and cement damage; to this end a number of studies investigated several prospective modifications. In some of these investigations less stress shielding and improved implant stability were observed in fully cemented fixations [23] and with poly-methyl methacrylate (PMMA) instead of other bioactive bone cements [24]. It was also revealed that shorter stems had improved the overall stability of the cemented fixation and provided the femur with more proximal load [25]. Implant shape modification techniques were also investigated in cemented and cementless fixations; common design optimizations in the former fixation targeted the cement layer or cement-prosthesis interface with the objective of minimizing stress concentration in these areas [26C28]; however stress shielding of the bone was not quantified for use in the design analysis. Several shape optimization models were developed for cementless prostheses where one [27, 29C32] or more [33C35] performance criteria were used in the search method. In the most relevant of these studies [35], a three-dimensional model of the implant based on the commercial Tri-Lock (Depuy, Inc., Warsaw, IN, USA) was constructed using suitable interpolation between a fixed 91396-88-2 supplier number of key cross sections and a simulation based structural optimization was used to identify new and improved designs. The major drawbacks of this form of optimization 91396-88-2 supplier are the computing cost which is usually expensive; additionally they are prone to a risk of being trapped 91396-88-2 supplier in local optima and the CAD interpretation of the shape optimization result is not trivial [36]. In.