Shoulder arthoplasty has increased in the last years and its main goal is to relieve pain and restore function. Shoulder prosthesis enters in the market without any type of pre-clinical tests. Within this paper we present study experimental and computational tests as pre-clinical testing to evaluate total shoulder arthoplasty performance. An in vitro experimental simulator was designed to characterize experimentally the intact and implanted shoulder glenoid articulation. Fourth generation Sawbones® composite left humerus and scapula were used and the cartilage was replicated with silicone for the intact articulation (figure 1). In the intact experimental articulation we considered the inferior glenohumeral ligament as an elastic band with equivalent mechanical properties. For the implanted shoulder, the Comprehensive® Total Shoulder System (Biomet®) with a modular Hybrid® glenoid base and Regenerex® central post was considered (figure 2). The prostheses were implanted by an experienced surgeon and clinical results from orthopedic registers were collected. The system structures were placed to simulate 90º in abduction, including the following muscle forces: Deltoideus 300N, Infraspinatus 120N, Supraspinatus 90N and Subscapularis 225N. The finite element model was created with tetrahedral linear elements with linear elastic and isotropic material for the humerus in figure 3, (Young's modulus for cortical bone − 16.5 GPa; trabecular bone − 124 MPa). Anisotropic behavior was considered for the scapula model (E11 = 342.1 MPa, E22 = 212.8 MPa, E33 = 194.4 MPa). The shoulder prosthesis was of polyethylene with 1GPa and titanium with 110 GPa. The Poisson's ratio was 0.3 in all material, except for polyethylene where we assumed a value of 0.4. A long-term post-operative condition was simulated.Introduction
Materials and methods
An increasing trend in the incidence of primary and revision bone replacements has been observed throughout the last decades, mainly among patients under 65 years old.10-year revision rates are estimated in the 5–20% range, mainly due to peri-implant bone loss. Recent advances allow the design of implants with custom-made geometries, nanometer-scale textured surfaces and multi-material structures. Technology also includes (bio)chemical modifications of the implants' surfaces. However, these approaches present significant drawbacks, as their therapeutic actuations are unable to: (1) perform long-term release of bioactive substances, namely after surgery; (2) deliver personalized stimuli to target bone regions and according to bone-implant integration states. Here we propose the design of instrumented active implants with ability to deliver personalized biophysical stimuli, controlled by clinicians, to target regions in the bone-implant interface throughout the patients' lifetime. The idea is to design bone implants embedding actuators, osseointegration sensors, wireless communication and self-powering systems. This work proposes an advanced therapeutic actuator for personalized bone stimulation, and a self-powering system to electrically supply these advanced implants.Introduction
The Innovative Concept
The number of total hip replacements (THR) increased around 3.5% by year in last decade. Osteoarthritis is the most important disease in the hip, with a prevalence of 10% in the older population (>85 years), according to the Swedish THA Register. THR have been increasing in last years, mainly in young patients between 45 to 59 years old. This type of patients needs a long term solution to prevent hip revision. Two commercial solutions for young patients, the resurfacing prosthesis and press fit one, were analysed in the present study by experimental and numerical models. Two synthetic left models of composite femur (Sawbones®, model 3403), which replicates the cadaveric femur, and two composite pelvic bones were used to introduce two Comercial models of Hip resurfacing (Birmingham model) and Press-fit stem (Laffit Selft –locking stem press-fit model). The commercial hip stems were chosen according to the femurs head size (resurfacing) and the femur size to press-fit Hip stem. Then, they were introduced by an experimented surgeon. The experimental set-up was applied according to a system defined previously by Ramos et al. (2013). Numerical models were implemented by replicating the experimental tests. A 3D scanning was used to identify the stem position in each model. The properties of cortical and cancel bone and hip prosthesis were also taken into account by these models. Contact was established in the interfaces for both press-fit solutions. The femur rotates distally and Pelvic moves up and down according model changes, in order to guarantee models with the same boundary conditions.Introduction
Methods
Hip resurfacing arthoplasty (HRA) is an alternative to total hip arthroplasty (THA), which has increased in the last years, especially in young patients. A suitable positioning of the resurfacing head is important, mainly because it is strongly related with the neck fracture. The goal of this work was to evaluate the influence of the resurfacing head positioning in the load distribution along the femurs’ structures. Using 3D scan technology, the exterior geometry of a composite femur, used to create the FE models, was obtained. Three resurfacing models were used in three different positions in the frontal plane. A model with a positive offset of +5mm (Resurfacing #1), in neutral position (Resurfacing #2), and with a negative offset of −5mm (Resurfacing #3) was developed. A Birmingham® Hip Resurfacing prosthesis was chosen according to the femurs’ head. It was positioned in the femur and acetabulum by an experimented surgeon. The metal on metal contact pair was implemented. Models were aligned with 7° and 9°, considering the position of the anatomical femurs in sagittal and frontal planes. Models were constrained on the wing of the ilium and ischial tuberosity, allowing only vertical and rotational movements on the iliac side. Femurs were constrained on its distal side, allowing only rotational movements.Introduction
Materials and methods
The orthopaedic market offers more than two hundred different hip femoral stems. Of these, very few have undergone scientific studies with published results. The differences of designs of the stem are mainly related to surface texture and geometry sections. The development of a new cemented hip prosthesis is certainly a very hard task if aiming the improvement of actual performance. This study presents the influence of geometric variables in a novel hip stem concept which was based on the comparison of the performance of the best cemented stems actually in the market. The study was developed using finite element analysis and experiments with in vitro femoral replacements. A numerical simplified model of the hip replacement was designed to generate the final geometry of the femoral stem section. After an in vitro cemented commercial stem was done, with the best cemented stem a Lubinus, Charnley, Stanmore and Müller. Realistic numerical models also allowed us to determine cement mantle stresses of commercial femoral stems that were compared with those obtained for the new concept stem. The new model was then prototyped and tested through in vitro fatigue tests. Finally fatigue tests were also performed to determine the density of cracks in the cement mantles, as well as debonding for both conventional and new designs.Introduction
Materials and Methods
