Date Published: March 5, 2019
Publisher: Public Library of Science
Author(s): Baptiste Poncery, Santiago Arroyave-Tobón, Elia Picault, Jean-Marc Linares, John Leicester Williams.
Looking for new opportunities in mechanical design, we are interested in studying the kinematic behaviour of biological joints. The real kinematic behaviour of the elbow of quadruped animals (which is submitted to high mechanical stresses in comparison with bipeds) remains unexplored. The sheep elbow joint was chosen because of its similarity with a revolute joint. The main objective of this study is to estimate the effects of elbow simplifications on the prediction of joint reaction forces in inverse dynamic simulations. Rigid motions between humerus and radius-ulna were registered during full flexion-extension gestures on five cadaveric specimens. The experiments were initially conducted with fresh specimens with ligaments and repeated after removal of all soft tissue, including cartilage. A digital image correlation system was used for tracking optical markers fixed on the bones. The geometry of the specimens was digitized using a 3D optical scanner. Then, the instantaneous helical axis of the joint was computed for each acquisition time. Finally, an OpenSim musculoskeletal model of the sheep forelimb was used to quantify effects of elbow joint approximations on the prediction of joint reaction forces. The motion analysis showed that only the medial-lateral translation is sufficiently large regarding the measuring uncertainty of the experiments. This translation assimilates the sheep elbow to a screw joint instead of a revolute joint. In comparison with fresh specimens, the experiments conducted with dry bone specimens (bones without soft tissue) provided different kinematic behaviour. From the results of our inverse dynamic simulations, it was noticed that the inclusion of the medial-lateral translation to the model made up with the mean flexion axis does not affect the predicted joint reaction forces. A geometrical difference between the axis of the best fitting cylinder and the mean flexion axis (derived from the motion analysis) of fresh specimens was highlighted. This geometrical difference impacts slightly the prediction of joint reactions.
The natural evolution of biological joints (articular geometry, material properties and mechanisms of tissue repair) has generated efficient joints in terms of mechanical performance. Looking for new opportunities in mechanical design, we are interested in studying the kinematic behaviour of biological joints. Unlike dorsomobiles, dorsostable mammals are able to stand for long periods. This study focuses on the kinematic behaviour of the elbow of a dorsostable mammal. This joint is interesting because of its similarity with a revolute joint.
In this section, the procedure used to determine the effects of joint simplification in musculoskeletal dynamic simulation is described. This procedure was divided in three steps as shown in Fig 1. The first one was focused on the measurement of kinematics during a flexion-extension gesture on cadaveric specimens (sheep elbow). The measurement was done using a digital image correlation (DIC) system; bones were also digitized using a 3D optical scanner. The second step consisted on data post-processing to develop a realistic kinematic model of the elbow. The third step introduced the developed kinematic model in a musculoskeletal model of the whole sheep forelimb for performing inverse dynamic simulations of a gait trial. These three steps are detailed in the rest of this section.
To the best of our knowledge, this article proposes the first 6 DoF kinematics analysis of the elbow of a quadruped animal. For this analysis, we conducted in vitro experiments over sheep elbow specimens performing extension–flexion motion. Looking for a high measuring precision, we used a DIC system for capturing bones motion. The fact of measuring directly over the bones avoided issues induced by soft tissue artifacts. This measured kinematics was implemented in a musculoskeletal model of a sheep forelimb to evaluate its impact in the prediction of joint reaction forces.