Musculoskeletal disorders are becoming an ever-growing societal burden and, as a result, millions of bone replacements surgeries are performed per year worldwide. Despite total joint replacements being recognized among the most successful surgeries of the last century, implant failure rates exceeding 10% are still reported. These numbers highlight the necessity of technologies to provide an accurate monitoring of the bone–implant interface state. This study provides a detailed review of the most relevant methodologies and technologies already proposed to monitor the loosening states of endoprosthetic implants, as well as their performance and experimental validation. A total of forty-two papers describing both intracorporeal and extracorporeal technologies for cemented or cementless fixation were thoroughly analyzed. Thirty-eight technologies were identified, which are categorized into five methodologies: vibrometric, acoustic, bioelectric impedance, magnetic induction, and strain. Research efforts were mainly focused on vibrometric and acoustic technologies. Differently, approaches based on bioelectric impedance, magnetic induction and strain have been less explored. Although most technologies are noninvasive and are able to monitor different loosening stages of endoprosthetic implants, they are not able to provide effective monitoring during daily living of patients.

OBJECT: The purpose of this study was to evaluate the failure risk of cervical vertebrae after total disc replacement with a keel-design prosthesis (ProDisc-C), taking into consideration the effects of vertebral body height, multilevel replacement, and the association with an adjacent fusion cage. Although promising clinical results have been reported for the ProDisc-C, some clinical studies have reported vertebral body–splitting fractures at single- and multilevel arthroplasty sites. This implant has central keels to provide solid initial stability, and some authors associate the potential risk of vertebral body failure with the keel design, especially in patients with small vertebral body height or when the implant is used at multiple levels. METHODS: The study was performed using a specimen-specific C4–6 cervical-segment finite-element model to assess the compressive strains on the C-5 vertebral body for each cervical segment configuration, and synthetic polyurethane models to experimentally predict the compressive load at failure for 3 vertebral body heights. RESULTS: The use of a keeled ProDisc-C prosthesis at multiple levels or in combination with a fusion cage increases by a factor of 2–3 the compressive strains at the C-5 vertebral body relative to single-level arthroplasty. All implanted segment configurations tested demonstrated a continuum of the load at failure and the vertebral body height, but no significant differences were found between the 3 vertebral body heights in each segment configuration. CONCLUSIONS: The use of a keeled ProDisc-C prosthesis at 2 adjacent levels or combined with a fusion cage presented the lowest load-at-failure values, 2 times higher on average than the ones occurring during physiological tasks. This fact indicates an identical and limited risk of vertebral body failure for these 2 segment configurations, whereas vertebral body height appears to slightly affect this risk. However, for some tasks that place higher physical demands on the neck, beyond what was represented by our models, there may also be risk of microdamage initiation, which is not present in the single-level arthroplasty.

Engineering techniques used to evaluate strain-stress fields, materials’ mechanical properties, and load transfer mechanisms, among others, are useful tools in the study of biomechanical applications. These engineering tools, as experimental and numerical ones, were imported to biomechanics, in particular in dental biomechanics, a few decades ago. Several experimental techniques have been used in dental biomechanics, like photoelasticity, ESPI (Electronic Speckle Pattern Interferometry), strain gages, and other kinds of transducers. However, these techniques have some limitations. For instance, photoelasticity and ESPI give the overall field pattern of the strain, showing the stress-strain concentration points. These methods cannot give an accurate measurement at all points. On the contrary, strain gages can be used to perform local measurements. However, as they use electrical resistances, their use is limited to perform in vivo measurements. Optical fiber sensors have already been used in dentistry, for diagnostic and therapeutic purposes, and in dental biomechanics studies. Lasers have also been used in clinical dentistry for a few decades. Other optical technologies, like optical coherence tomography (OCT), became suitable for dental practice and nowadays it is perhaps one that has had more development in dentristry, along with lasers.

The shoulder joint is a complex anatomical system. The main goal of this study was to build a Finite Element (FE) model of the intact shoulder joint and its validation was done using an experimental model comparing cortical strains. Considering the expected differences between the experimental model and an in vivo shoulder, the experimental model developed replicates adequately the in vivo functioning of the joint. For the experimental model we used 4th generation composite bone structures of the humerus and scapula, including the humeral head cartilage, the glenoid cartilage and glenohumeral ligaments. The model also comprises the most important muscles in abduction. The FE model of the intact shoulder was developed mimicking the experimental model regarding the geometry of the bone structures. Strain gage rosettes were used to measure strain responses loading bone structures positioned in a 90° abduction angle. The accuracy of the strains calculated (numerical model) and measured (experimental model) was evaluated with linear regression analysis. The correlation coefficient of 0.76 and RMSE of 107 µε indicate an adequate agreement between numerical and experimental strains. The experimental procedure to simulate the biomechanics of the intact shoulder joint is a difficult task due to the instability of the joint and the number of structures that compose it. The use of FE models is necessary to perform more complex biomechanical studies, which are normally impossible to make with experimental ones, highlighting the importance of validation of FE models. The results of these models can then be used to compare with clinical data considering, however, the inherent characteristics of numerical simulations and differences relatively to clinical models.

A significant number of papers relatively to the investigation made on Anterior Cruciate Ligament (ACL) Reconstruction (ACLR) has been published in orthopaedic related journals. Finite Element (FE) Analysis (FEA) has been used to predict the performance of biomechanical-biomedical systems as well as the effect of clinical factors on the ACLR success.