Experimental simulation of cyclic, six degree-of-freedom, gait and sit-to-stand loading waveforms using a six-axis...

Area of Science:

• Biomechanics
• Spinal Engineering
• Orthopedic Research

Background:

• In vitro spinal load simulation is crucial for understanding spinal biomechanics.
• Current methods often use limited degrees-of-freedom (DOF), failing to replicate complex 6DOF spinal movements.
• This gap limits the accurate assessment of spinal behavior during daily activities.

Purpose of the Study:

• To develop and validate a comprehensive in vitro testing method for applying cyclic six degrees-of-freedom (6DOF) loading profiles.
• To simulate physiologically relevant gait and sit-to-stand (S2S) activities on lumbar spinal motion segments.
• To evaluate the accuracy and feasibility of the developed 6DOF simulation technique.

Main Methods:

• Eight cadaveric lumbar spinal segments were tested.
• Initial 1DOF pure moment testing (flexion-extension, lateral bending, axial rotation) was performed.
• Subsequent 6DOF gait and S2S simulations were conducted under quasi-static and dynamic loading rates, including a 10,000-step gait simulation using iterative learning control (ILC).

Main Results:

• No significant changes in spinal range of motion were observed after 10,000 gait steps.
• Root mean square error was generally below load cell resolution, except in short-duration dynamic gait/S2S tests.
• Iterative learning control (ILC) achieved load accuracy convergence within 4-10% during longitudinal gait testing.

Conclusions:

• The developed 6DOF simulation method is feasible for replicating real-world lumbar spine loading conditions.
• This approach allows for a more accurate evaluation of lumbar spine biomechanics under physiologically derived loading.
• The technique holds promise for advancing in vitro spinal research and understanding spinal health.