Long-Term Remodeling in Proximal Femur Around a Hydroxyapatite-Coated Anatomic Stem

Simulation by Finite Elements of Bone Remodeling After Implantation of Femoral Stems

“…The monitoring of an anatomic femoral stem with metaphyseal load-bearing and HA coating (ABG-I), that was carried out through a prospective, controlled study that included 67 patients (Group I) in the period 1994-99, has confirmed that even though the clinical results are very favourable, a high percentage of cases with stress-shielding are detected (Herrera et al, 2004). This results in a proximal atrophy which has been quantified with DXA (Panisello et al, 2009a). For that reason the stem has been redesigned (ABG-II) in an attempt to improve the proximal transfer of loads and reduce the phenomenon of stress-shielding.…”

“…Prior to the development of our FE models several long-term studies of bone remodeling after the implantation of two different cementless stems, ABG I and ABG II, were performed Panisello et al, 2009a;Panisello et al, 2009b). These studies were performed using DXA, a technique that allows an accurate assessment of bone density losses in the different Gruen zones.…”

“…On the other hand the TMZF alloy which is used on the ABG-II stem has a Young's modulus of 74-85 GPa, according to the manufacturer information, using a mean value of 79.5 GPa in the different analyses. Taking various studies as reference (Kerner et al, 1999;Turner et al, 2005), a linear relationship between the bone mass values, which come from the medical study collected in Panisello (Panisello, 2009a), and the apparent density was established in addition to a cubic relationship between the latter and the elastic modulus, using a maximal Young's modulus of 20 GPa, thereby obtaining the cortical bone modulus of elasticity values for each one of the 7 Gruen zones. To carry out the analysis of the results, the cortical bone of each model is divided into seven zones which coincide with the Gruen zones.…”

“…To carry out the analysis of the results, the cortical bone of each model is divided into seven zones which coincide with the Gruen zones. The elastic modulus obtained from the values in Panisello (Panisello, 2009a) was used as an input in the cortical bone. These values are being successively adjusted for each one of the models (femur with ABG-I stem and femur with ABG-II stem) in different moments of time: post-operative, 6 months, 1, 3 and 5 years.…”

Computer simulating a clinical trial of a load-bearing implant: An example of an intramedullary prosthesis

“…As Frost (1987) speculated, each individual's bone tissue has a somewhat different response to mechanical stress-and this mechanosensitivity will also vary with age; some patients' bone tissue will be indifferent to the change in stress whereas other bone tissue will be mechanosensitive to a considerable degree leading to different amounts of bone resorption around the implant, or different patterns of bone ingrowth. Many follow-up studies have shown great variation; recently for example Panisello et al (2009) showed that an anatomic non-cemented stem had bone loss which ranged from 12% to 27% after 1 post-operative year.…”