Article

A non-articulated plantarflexion resist ankle foot orthosis (AFO),
commonly known as a posterior leaf spring AFO, is indicated for patients with
motor impairment to the dorsiflexors. The AFO is often custom molded to a
patient's lower limb anatomy and fabricated from polypropylene. There are no
established guidelines for fabricating this type of AFO with predetermined
stiffness of the ankle region for normal walking speeds. Therefore an AFO may not
meet the biomechanical needs of the patient. Objectives:
Quantify the
biomechanical ankle stiffness requirement for an individual with complete
dorsiflexor impairment and develop a method for fabricating an AFO with ankle
stiffness to meet that requirement. Study Design: Experimental, bench research.
Methods: The literature on sagittal biomechanics of non-pathological adults was
reviewed to derive the stiffness of the ankle during loading response. Computer
models of 144 AFOs were created with geometric variations to account for
differences in human anthropometrics. Computer-based finite element analysis was
employed to determine the stiffness and safety factor of the models. Results:
Stiffness of the AFOs ranged from 0.04 to 1.8 Nm/deg.
This ample range is
expected to account for the stiffness required for most adults with complete
dorsiflexor impairment. At 5 degrees deflection the factor of safety (ratio of
strength to stress) ranged from 2.8 to 9.1. A computer program was generated that
computes AFO stiffness from user-input variables of AFO geometry. The stiffness
is compared to a theoretically appropriate stiffness based on the patient mass.
The geometric variables can be modified until there is a close match, resulting
in AFO design specification that is appropriate for the patient. Conclusion:
Through validation on human subjects, this method may benefit patient outcomes in
clinical practice by avoiding the current uncertainty surrounding AFO performance
and reducing the labor and time involved in rectifying a custom AFO post-fabrication. Clinical relevance This method provides an avenue for improving
patient outcomes by avoiding the current uncertainty surrounding non-articulated
plantarflexion resist ankle foot orthosis performance. The ability to quantify
the biomechanical ankle stiffness requirement for an individual with complete
dorsiflexor impairment provides insight into how other AFO types should be designed as well.

Langue : ANGLAIS