Development of a theoretical model for upright postural control in lower limb prosthesis users.

Area of Science:

• Biomechanics
• Rehabilitation Engineering
• Human Movement Science

Background:

• Assessing quiet standing in unilateral prosthesis users often relies on the inverted pendulum model, though its validity is debated.
• A unilaterally-constrained pin-controller model offers a potential alternative for explaining postural control mechanisms.

Purpose of the Study:

• To evaluate the validity of a unilaterally-constrained pin-controller model in explaining postural control in individuals with unilateral lower-limb prostheses.
• To compare postural control in prosthesis users and able-bodied individuals against the proposed theoretical model.

Main Methods:

• Participants (unilateral prosthesis users and able-bodied controls) performed quiet standing tasks under various sensory conditions (eyes open, eyes closed, visual feedback).
• A platform unilaterally constrained the center of pressure (CoP) movement for controls to simulate prosthetic limb conditions.
• Kinematic (body markers) and kinetic (CoP) data were collected to calculate correlation coefficients inferring inverted pendulum behavior.

Main Results:

• Kinematic data showed high-magnitude inverted pendulum behavior in both mediolateral and anteroposterior directions for all participants.
• Kinetic data revealed model validity in the anteroposterior direction, with strong correlations for unconstrained/intact limbs and combined conditions, but weaker for constrained/prosthetic limbs.
• Mediolateral direction kinetic data showed negligible coefficients for individual limbs and moderate to large negative correlations irrespective of group.

Conclusions:

• Postural control in both unilateral prosthesis users and able-bodied individuals aligns well with the predictions of a unilaterally-constrained pin-controller model.
• The findings have significant implications for understanding the fundamental control of posture in individuals with transtibial prostheses.