A New Test Rig for In-Vitro Evaluation of the Knee Joint Behaviour

The evaluation of the knee joint behavior is fundamental in many applications, such as joint modeling, prosthesis and orthosis design. In-vitro tests are important in order to analyse knee behavior when simulating various loading conditions and studying physiology of the joint. A new test rig for in-vitro evaluation of the knee joint behavior is presented in this paper. It represents the evolution of a previously proposed rig, designed to overcome its principal limitations and to improve its performances. The design procedure and the adopted solution in order to satisfy the specifications are presented here. Thanks to its 6-6 Gough-Stewart parallel manipulator loading system, the rig replicates general loading conditions, like daily actions or clinical tests, on the specimen in a wide range of flexion angles. The restraining actions of knee muscles can be simulated when active actions are simulated. The joint motion in response to the applied loads, guided by passive articular structures and muscles, is permitted by the characteristics of the loading system which is force controlled. The new test rig guarantees visibility so that motion can be measured by an optoelectronic system. Furthermore, the control system of the new test rig allows the estimation of the contribution of the principal leg muscles in guaranteeing the equilibrium of the joint by the system for muscle simulation. Accuracy in positioning is guaranteed by the designed tibia and femur fixation systems,which allow unmounting and remounting the specimen in the same pose. The test rig presented in this paper permits the analysis of the behavior of the knee joint and comparative analysis on the same specimen before and after surgery, in a way to assess the goodness of prostheses or surgical treatments

Nuovo modello cinetostatico della caviglia umana.

The relevance of human joint models has been shown in the literature. They can help in diagnosis, in prostheses and ortheses design and in predicting the joints’ behavior. Recently a sequential approach for the modeling of the human diarthrodial joints composed of three steps has been proposed. At each step the role of some anatomical structures is considered. Starting from a limited number of structures, the model gets more and more sophisticated until all the components, both passive (articular surfaces, ligaments and tendons) and active (muscles), are incorporated in the final model. According to this procedure, the behavior of the human ankle during passive motion (no loads applied) has been previously modeled by a one degree of freedom 5-5 fully parallel mechanism. Starting from this model, the kinetostatic model of the human ankle joint that replicates its behavior when external loads are applied is developed. The anatomical and mechanical characteristics and the role of the passive structures are considered; a multifiber model is developed and an optimization criteria based on experimental data is proposed. Finally an application of the developed model to an amputated ankle is presented, together with the results obtained from the optimization of the geometrical and mechanical Parameters. Although some improvements can be achieved, the model is satisfactorily able to replicate the behavior of the human ankle subject to the anterior drawer and the inversion clinical tests applied in the neutral position

A Three-Dimensional Ankle Kinetostatic Model to Simulate Loaded and Unloaded Joint Motion

A kinetostatic model able to replicate both the natural unloaded motion of the tibiotalar (or ankle) joint and the joint behavior under external loads is presented. The model is developed as the second step of a sequential procedure, which allows the definition of a kinetostatic model as a generalization of a kinematic model of the joint defined at the first step. Specifically, this kinematic model taken as the starting point of the definition procedure is a parallel spatial mechanism which replicates the ankle unloaded motion. It features two rigid bodies (representing the tibia\u2013fibula and the talus\u2013calcaneus complexes) interconnected by five rigid binary links, that mimic three articular contacts and two nearly isometric fibers (IFs) of the tibiocalcaneal ligament (TiCaL) and calcaneofibular ligament (CaFiL). In the kinetostatic model, the five links are considered as compliant; moreover, further elastic structures are added to represent all the main ankle passive structures of the joint. Thanks to this definition procedure, the kinetostatic model still replicates the ankle unloaded motion with the same accuracy as the kinematic model. In addition, the model can replicate the behavior of the joint when external loads are applied. Finally, the structures that guide these motions are consistent with the anatomical evidence. The parameters of the model are identified for two specimens from both subject-specific and published data. Loads are then applied to the model in order to simulate two common clinical tests. The model-predicted ankle motion shows good agreement with results from the literature

A new test rig for static and dynamic evaluation of knee motion based on a cable-driven parallel manipulator loading system

The evaluation of the knee joint behavior is fundamental in many applications, such as joint modeling, prosthesis and orthosis design. A new test rig for in vitro analysis of the knee joint behavior is presented in this paper. Based on a cable-driven parallel manipulator loading system, the rig can simulate general knee loading conditions, such as clinical tests and common daily activities like walking and sit to stand, in a wide range of flexion angles. The joint natural response in terms of movement is measured by an optoelectronic system. Furthermore, the new rig allows the estimation of the contribution of the principal leg muscles in guaranteeing the equilibrium of the joint. Despite its simplicity and low cost, the rig presents good accuracy, repeatability and versatility that allows its application on a wide range of specimen sizes. It represents an advanced application of cable-driven parallel robots for in vitro motion analysis of the knee subjected to general loads

A new test rig for static and dynamic evaluation of knee motion based on a cable-driven parallel manipulator loading system

The evaluation of the knee joint behavior is fundamental in many applications, such as joint modeling, prosthesis and orthosis design. A new test rig for in vitro analysis of the knee joint behavior is presented in this paper. Based on a cable-driven parallel manipulator loading system, the rig can simulate general loading conditions, such as clinical tests and common daily activities, in a wide range of flexion angles. The joint natural response in terms of movement is measured by an optoelectronic system. Furthermore, the new rig allows the estimation of the contribution of the principal leg muscles in guaranteeing the equilibrium of the joint. Despite its simplicity and low cost, the rig presents good accuracy, repeatability and versatility that allow its application on a wide range of specimen sizes. It represents an advanced application of cable-driven parallel robots for in vitro motion analysis of the knee subjected to general loads

Measure and analysis of motion and muscle forces at the human knee during dynamic motion tasks

The characterization of the joint behaviour under physiological loading condition is a necessary step to come to the definition of significant joint models, which open the way to the identification of better treatments and prosthesis and orthosis designs. A test rig has been recently developed, capable to replicate a generic loading condition while measuring the relative motion of the bones participating to the articulation and estimating the associated muscular forces. In this paper, the rig architecture and functioning will be briefly recalled. Then, the result of its application on a knee joint will be presented

A Test Rig for the Analysis of the Knee Under Dynamic Motion Tasks

A new test rig for measuring the knee joint motion under generic dynamic motion tasks was developed. The rig allows estimation of the muscle forces required by a given task. The rig proved high accuracy and repeatability of measurements, despite its simplicity and low cost. In this paper, the main characteristics of the test rig are presented together with some recent experimental results