The complex biomechanics and morphology of the proximal femur epiphyses are presented. This particular region of the human thighbone is characterized by high flexibility compared to other primates, as it evolved lighter and lasted longer due to the vertical position of humans and more balanced loading. The nature and fine morphology of the head of the femur and its structural behavior have been investigated.
Introduction
Orthopedic prostheses in use today are mainly made of metal and ceramic materials with exceptional strength and stiffness properties but high physiological invasiveness. These systems, while guaranteeing the functional tenure of biomechanics, often severely disrupt the physiology of human bones.
This invasive is particularly evident for hip joint replacement using a rigid full metal prosthesis. Human bipedal gait and vertical posture have led to the unique and sizeable evolution and adaptation of the osseous systems of the femur, pelvis, hip and lumbar (Aversa et al., 2016 ao, 2017 ae; Petrescu et al., 2015, 2016 ae; Petrescu and Calautit, 2016 ab; Mirsayar et al., 2016-2017).
Trabecular Metal Primary Hip Prosthesis
The complex evolution of trabecular bone position and morphology in human proximal bone is mainly determined by a stress pattern in which bone is retained only in areas where it undergoes a sufficiently tense mechanical stimulus and is lost when it is not (Lovejoy 1988, 2002, 2005).
Therefore, the clinical efficiency and long-term reliability of hip joint prostheses require a deeper understanding of the biomechanical invasiveness of current restorative replacement. These products, which are made from traditional technologies such as melting and mechanical machining, do not hold flexible design solutions that allow for the fine integration of biomechanical bone in the biologically complex structure of the femur. Moreover, this traditional solution is inadequate for younger patients who have high life expectancy and then high prosthetic requirements in terms of duration and biomechanical osseointegration.
A new generation of prostheses with better biomechanical osseointegration with living bone is then required.
In particular, additive technologies using Titanium or Cobalt Chrome alloys, due to the eclecticism of their processes in producing high-strength complex trabecular structures, may represent a new generation of flexible trabecular bio-prosthetic components production in the future.
Studies on prosthetic biomimetics involving this innovative fabrication process (Annunziata et al., 2006; Apicella et al., 2010; Aversa et al., 2009, 2016) have opened up the definition of new design criteria for the production of more biomechanically compatible prostheses. Figure 1 depicts a biomimetic approach using silico, in vitro, and in vivo validation steps for biofidel bone modeling.
Mandibular and femur biofidel models have been presented in previous publications (Apicella et al., 2010; Gramanzini et al., 2016; Perillo et al., 2010; Sorrentino et al., 2007; 2009).
The authors, starting from this study, have investigated the potential of additive manufacturing technologies that are still not fully exploited. In addition, advances in our biomimetic design procedures, which have allowed us to conceptually develop new biomimetic dental implants (Aversa et al 2009) and new trabecular prostheses, could lead to new prosthetic systems that better mimic the biomechanical behavior of the thigh (Aversa et al 2016). .
The human thighbone has an internal light trabecular structure which, through evolutionary optimization of the mass and morphology of cortical and trabecular bone types (Walker et al 1985, Bruno et al 1999, Oh and Harris, 1978; Tamar and Hashin, 1980), has been able to develop mechanical properties. which can withstand high external pressures (Ashman et al., 1984; Dalstra et al., 1993).
Human bipedal gait and vertical posture have led to a unique and sizable adaptation of the osseous systems of the femur, pelvis, hip and lumbar. In particular, the hip joint acquires a much more extended position. The human thighbone, which is basically loaded in a vertical position, has evolved to be lighter and longer than other primates where it is loaded horizontally.
This morphological evolution is due to the fact that the neck of the thigh of the limb in the vertical stand is loaded as a cantilever beam, and can then be related to the smaller bending moments produced in humans.
The evolutionary pathway of the human hip has been extensively reviewed (Lovejoi 2005) to explain the unusual cortico-trabecular structure of the proximal femur, which presents a cortical bone that is definitely thickened only in certain locations (Figure 2 right).
In particular, as reported by Lovejoy et al (1988), the head of the thigh thickens the cortex only near its lower part while it indicates a practically complete absence of cortex in the top as reported in Figure 2 right).