Meeting Abstract
Musculoskeletal systems can be classified into one of two types of mechanisms: open-chain versus closed-chain. In open-chain mechanisms, joints form open branches (e.g. vertebrate limbs) while in closed-chain mechanisms, joints connect back on themselves to form closed loops (e.g. the cranial linkages of fishes). While for both types of mechanism, motion is constrained by the individual joints, in closed-chain mechanisms the joint chains themselves impose an additional motion constraint. However, for biomechanical closed-chain systems it remains unknown which imposes a greater motion constraint: the joints themselves or the linking of joints together into a closed chain. To answer this question we collected 3D in vivo kinematics of seven cranial bones in channel catfish during suction feeding using X-ray Reconstruction of Moving Morphology (XROMM). We then fit single-joint and multibody models of varying degrees of freedom (DoFs) to the in vivo kinematics of the hyoid-pectoral girdle mechanism, which expands the mouth during suction feeding. We find that the hyoid-pectoral girdle mechanism functions as a 6-body linkage with at least 3 DoFs, revealing higher mobility than found by previous 2D kinematic studies. Yet, as an open chain the hyoid-pectoral girdle mechanism would have at least 11-12 DoFs. Thus, in this mechanism the linking of joints into a closed loop imposes the primary motion constraint, reducing the DoFs by over 70%. These results demonstrate a significant biomechanical consequence of simply connecting joints into closed chains, which may underlie a fundamental difference in the function and control of open- versus closed-chain motor systems. Funded by NSF 1612230, 1655756.
