Evaluating Knee Mechanisms for Assistive Devices.

Area of Science:

• Biomechanics and Assistive Device Technology
• Orthotics and Rehabilitation Engineering

Background:

• Human knee joints have complex, non-singular rotation axes, unlike current knee braces.
• Existing knee brace mechanisms (single axis, predefined polycentric) can cause misalignment, leading to discomfort, migration, and device abandonment.

Purpose of the Study:

• To compare the effects of three knee brace joint mechanisms—single axis (SA), polycentric with predefined centrode (PPC), and polycentric with self-aligning center of rotation (PSC)—on device migration and interaction forces.
• To evaluate the impact of knee joint mechanisms as the sole variable on brace performance.

Main Methods:

• Designed and conducted an experiment comparing SA, PPC, and PSC knee brace mechanisms.
• Kept brace material, weight, size, cuff design, fitment, and tightness consistent across all trials.
• Measured device migration and interaction forces on brace straps during use.

Main Results:

• No significant differences in walking kinematics or kinetics were observed across the three mechanisms.
• The PPC brace exhibited greater interaction forces on the top strap compared to SA and PSC braces.
• The PSC and SA braces showed lower interaction forces on the bottom strap than the PPC brace.
• The PSC brace demonstrated significantly less migration than both SA and PPC braces.

Conclusions:

• Predefined polycentric knee brace mechanisms may not be universally beneficial for users.
• Polycentric self-aligning mechanisms show potential for improving knee brace alignment and reducing device migration.
• The PSC mechanism may enhance user comfort and adherence by minimizing brace movement and pressure points.