Introduction to Force-Dependent Kinematics: Theory and Application to Mandible Modeling

Area of Science:

• Biomechanics
• Musculoskeletal Modeling
• Orthopedic Surgery

Background:

• Accurate estimation of muscle, ligament, and joint forces is crucial for orthopedic surgery planning.
• In vivo measurement of these forces is not feasible, necessitating the use of musculoskeletal models.
• Existing models often use idealized joints, which are inadequate for non-ideal joint structures.

Purpose of the Study:

• To present the mathematical framework of a novel musculoskeletal modeling approach: force-dependent kinematics (FDK).
• To enable simultaneous computation of muscle, ligament, and joint forces, along with internal joint displacements.
• To account for contact surfaces and ligament structures in joint mechanics.

Main Methods:

• Implemented the FDK method into the Anybody modeling system.
• Developed a subject-specific mandible model using FDK.
• Compared the FDK model against a point-on-plane (POP) model.
• Validated models against measured joint kinematics during simulated chewing and jaw movements.

Main Results:

• Both FDK and POP models accurately estimated joint kinematics (RMSD < 1.7 mm).
• The POP model showed slightly better kinematic prediction (RMSD < 0.75 mm).
• Significant differences in estimated joint forces were observed (RMSD up to 24.7 N), highlighting model dependency.

Conclusions:

• The FDK methodology is capable of creating joint models that incorporate geometry and elasticity.
• This approach offers a more detailed understanding of joint mechanics compared to idealized models.
• Further refinements to the mandible model are possible, but FDK shows significant potential for joint modeling.