A generalized framework for determination of functional musculoskeletal joint coordinate systems

Area of Science:

• Biomechanics
• Orthopedic Surgery
• Medical Imaging

Background:

• Establishing anatomical coordinate systems (CS) is crucial for joint kinematics analysis.
• Current methods relying on anatomical landmarks are sensitive to observer variability, impacting results.
• This variability can significantly affect the interpretation of joint motion and loading.

Purpose of the Study:

• To introduce an objective method for calculating functional CS definitions for bones in joints.
• To apply this method to tibiofemoral joint specimens using three-cylindrical-joint kinematic chain decomposition.
• To compare the reproducibility and accuracy of functional CSs against traditional anatomical CSs.

Main Methods:

• Developed a functional CS method driven by low-resistance joint motion during loading.
• Applied the method to twelve tibiofemoral joint specimens, collecting data during passive flexion and rotation.
• Utilized linear least squares minimization to redefine tibial and femoral origins and axes based on observed kinematics.

Main Results:

• Functional CSs demonstrated significant improvements in reproducibility: 7.4 mm for tibia origin (p < 0.001), 3.4 mm for femur origin (p < 0.001), and 2.9° for femur flexion-extension axis (p < 0.001).
• Functional CSs led to significant reductions in off-axis motion during passive flexion.
• Minimized kinematic cross-talk, allowing for clearer interpretation of joint responses to loading.

Conclusions:

• The proposed functional CS method offers an objective approach to defining joint coordinate systems.
• This method significantly reduces observer error in CS establishment, enhancing kinematic analysis reliability.
• Functional CSs improve the accuracy of joint kinematics, facilitating better understanding of joint function and response to biomechanical loads.