EFFECTS OF ARTICULAR CARTILAGE SHAPE AND MUSCLE ACTIVATION PATTERNS ON THE ELBOW JOINT KINEMATICS OF DREADNOUGHTUS SCHRANI

When investigating joint biomechanics, previous studies have found that when using six degrees of freedom, the shapes of articular surfaces affect the resulting kinematics, which are crucial to understanding the biomechanics of extinct organisms. One such study examined a model of the elbow of Dreadnoughtus schrani with six degrees of freedom and various articular cartilage surfaces, finding that the shape of the articular cartilage affected the resulting kinematics of elbow flexion; however, these variations were not explored in detail. Dreadnoughtus is one of the most complete giant titanosaurian sauropod dinosaurs. Using this model and the multi-body dynamic simulation program Adams, we investigated how kinematics differed during elbow flexion when cartilage shape, muscle forces, and active muscles were varied. We tested three reconstructions of articular cartilage, four variations in active muscles (Mm. humeroradialis, brachialis, and biceps), and several muscle force magnitudes. Each simulation was conducted to the maximum degree of flexion. Clinical rotations (e.g., flexion/extension) and translations (e.g., sliding dorsally) were calculated in Adams. Simulations were compared among each of the three cartilage reconstructions (e.g., how muscle variations affect the kinematics) and across these cartilage reconstructions (e.g., how cartilage shape variations affect the kinematics). Generally, we found that the position of the articular cartilage and muscle activation patterns affected joint kinematics. For example, when all muscles are active, it takes the same force to bring the elbow to maximum flexion across all positions of the articular cartilage. Conversely, when only the M. brachialis is active, it takes more time steps for certain simulations to reach maximum flexion when the same muscle force is applied. Additionally, the M. humeroradialis required the least amount of force to reach maximum flexion of any single muscle. Our results advance understanding of the biomechanics of the forelimb of Dreadnoughtus, which more broadly applies to understanding how variations in the shape of articular cartilage can affect limb kinematics.