Estimation of muscle forces for treadmill gait trials

Subject-specific musculoskeletal models and computational walking models in general have come a long way in improving clinical treatment of walking disorders. But more accurate predictions of such forces and their locations can help in designing knee replacements to recover normal walking. This project aims to predict muscle forces for treadmill gait trials when varying speeds and analyse the differences in those muscle forces. Three walking trials with different speeds were studied in this project. Two approaches were used to predict forces. In Approach A, knee contact force information was used as input of the algorithm, and in Approach B, these data was used only to validate the results. An OpenSim musculoskeletal model of the right leg was used to obtain inverse kinematics and inverse dynamics data, and muscle length and moment arms. The algorithm to estimate muscle forces consisted of a two-level nested optimization. The outer level optimizes the time-independent parameters and the inner level optimizes the time-dependent parameters. Kinematics and ground reaction force data used in this project were obtained from the fourth grand challenge competition to predict in vivo knee loads. Muscle force estimation values obtained in Approach B (usual case) were significantly different from Approach A (unique case) for most muscles. The results from this study reinforce results of previous studies. Medial and lateral force distribution was also analysed. The muscles with the maximum and minimum differences in mean forces for the three different speeds were identified and possible reasons for these differences were discussed

The application of impantable sensors in the musculoskeletal system: a review

As the population ages and the incidence of traumatic events rises, there is a growing trend toward the implantation of devices to replace damaged or degenerated tissues in the body. In orthopedic applications, some implants are equipped with sensors to measure internal data and monitor the status of the implant. In recent years, several multi-functional implants have been developed that the clinician can externally control using a smart device. Experts anticipate that these versatile implants could pave the way for the next-generation of technological advancements. This paper provides an introduction to implantable sensors and is structured into three parts. The first section categorizes existing implantable sensors based on their working principles and provides detailed illustrations with examples. The second section introduces the most common materials used in implantable sensors, divided into rigid and flexible materials according to their properties. The third section is the focal point of this article, with implantable orthopedic sensors being classified as joint, spine, or fracture, based on different practical scenarios. The aim of this review is to introduce various implantable orthopedic sensors, compare their different characteristics, and outline the future direction of their development and application

Design and integration of an instrumented knee prosthesis

Total knee arthroplasty is nowadays one of the most important orthopedic surgery. It consists of a procedure in which parts of the knee are replaced by a prosthesis. The largest indication for total knee arthroplasty is osteoarthritis, a knee disease that can cause the cartilage of the femur and tibia to wear away, so that the bones rub together with use. The major risk factors for osteoarthritis are aging and obesity. Both the life expectancy and the obesity rate are increasing in the developed countries, thus the number of estimated total knee arthroplasties is growing over the years. Although over one million of prosthetic joints are implanted every year in the developed countries, none of them contains sensors to help the orthopedic surgeons in improving the precision of the replacement surgery. The goal of this study is to design an electronic system to be embedded inside a total knee prosthesis, in order to measure the force applied to it and its kinematics. Providing the orthopedic surgeons with quantitative data on the biomechanics of the prosthetic knee can help them in improving the implant precision and, as a consequence, could reduce the risk of an early revision surgery. In the frame of this thesis, we worked with the F.I.R.S.T. prosthesis by Symbios Orthopedie SA, that was instrumented with sensors and electronics to measure, process and transmit force and kinematics data to an external reader. The constraints in the design have been established by the medical doctors and the prosthesis manufacturer and the technical solutions adopted are presented. In order to simplify a future approval for human tests, we decided to keep the shape of the knee artificial joint. To achieve that, we put all the sensors and the electronics inside the middle part of the prosthesis, constituted of a polyethylene insert located between the metallic parts of the artificial joint and whose function is to reduce the rubbing. An original encapsulation was designed to guarantee the bio-compatibility of the instrumented prosthesis and to avoid a potentially dangerous contact between the electronics and the human body. This should be ensured even in case of extreme wearing of the polyethylene insert, that can occur some years after the prosthesis implant and is one of the main indications for a revision surgery. The sensors were tested by using mechanical simulators of the knee joint and validated by means of reference sensors. Different demonstrators have been designed, from the first, with only the sensors located inside the prosthesis and all the electronics fabricated in a large-scale outside of it, to the last miniaturized versions, that can be entirely embedded inside the prosthesis. Moreover, an autonomous sensor for balancing the ligaments tension during the knee replacement surgery was designed, fabricated and tested. Such a device could be an important help for the medical doctors during the surgery to improve the precision of the implant and, being not-implantable, could easily obtain an approval for human clinical trials

Investigating the ideal deltoid kinematics and tension in reverse shoulder arthroplasty (RSA).

The shoulder is the one of the most active joints within the human body. Recruited in the majority of daily activities either in active use such as moving/carrying of objects or as a source of stability during locomotion. Therefore painful shoulder or its reduced mobility and function can be very debilitating hence affecting the quality of life. While shoulder pain and restricted motion encompasses a diverse array of pathologies, the most common causes are due to infection, arthritis, or trauma. Arthroplasty (the surgical reconstruction or replacement of a joint) of the shoulder has offered the potential for improved function and pain relief where the native structures have been damaged. The conventional total shoulder replacement, however, is not beneficial for all patients and may result in further pain and limited motion in persons with arthritic shoulders with a deficient rotator cuff. For these patients Reverse Shoulder Arthroplasty (RSA), in which anatomic concavities of glenohumeral joint are inverted, is a popular treatment. However, for optimal restoration of motion, the correct positioning of the glenohumeral centre of rotation and initial setting of the deltoid length (Deltoid Tension) must play an important role in the surgery outcome. A study of the key literature has shown that despite common use of RSA, its biomechanical characteristics during motion are not fully understood. This study investigates the influence of some of the key parameters on the intensity of forces and moments in the shoulder joint before, during and after RSA. These parameters include; geometry, kinematics and muscle passive force measurement (deltoid pretension measurement). To investigate the effect of geometrical changes on kinematics of shoulder after RSA, a musculoskeletal model of the shoulder is developed and simulated. Geometrical parameters of the musculoskeletal model are extracted from previous published studies. Results of the simulation enabled the detection of key parameters in reverse shoulder kinematics and its influence on determining the mechanical advantage of the shoulder mechanism. This identified the need for developing an X-ray imaging protocol and image processing tool that enable surgeons to predict optimum implants insertion position and estimate the performance of the shoulder before planning the operation. Subsequently, an assessment tool was proposed to assess shoulder Range of Motion (ROM) and deltoid muscle activity to both quantify and validate the predicted outcome of the surgery. The main purpose of this study is to measure the passive force exerted on the reverse shoulder joint during surgery as a criterion or measure of deltoid pretension. Hence a force sensor is designed, developed and tested in a custom built joint simulator. As part of this research and to allow objective assessment of the joint, a series of tools/hardware/software were proposed, designed and developed, and then tested and evaluated for effectiveness and functionality. The introduction of a system proposed here provides data which could be recorded in a database along with geometrics and kinematics pre and post operatively, residual force in glenohumeral joint intraoperatively and shoulder performance in terms of range of motion and EMG muscle activity of individual patients pre and post operatively. Such a database in time will enable us to find correlations between these parameters and the outcome of surgery in the long term. It is hoped that this will provide a tool for surgeons in future operations to who choose to use a more quantitative and repeatable way of optimizing the implant size and position accordingly

Enclosed Electronic System for Force Measurements in Knee Implants

Total knee arthroplasty is a widely performed surgical technique. Soft tissue force balancing during the operation relies strongly on the experience of the surgeon in equilibrating tension in the collateral ligaments. Little information on the forces in the implanted prosthesis is available during surgery and post-operative treatment. This paper presents the design, fabrication and testing of an instrumented insert performing force measurements in a knee prosthesis. The insert contains a closed structure composed of printed circuit boards and incorporates a microfabricated polyimide thin-film piezoresistive strain sensor for each condylar compartment. The sensor is tested in a mechanical knee simulator that mimics in-vivo conditions. For characterization purposes, static and dynamic load patterns are applied to the instrumented insert. Results show that the sensors are able to measure forces up to 1.5 times body weight with a sensitivity fitting the requirements for the proposed use. Dynamic testing of the insert shows a good tracking of slow and fast changing forces in the knee prosthesis by the sensors